trimaran aka

Professional BoatBuilder Magazine

Folding multihulls.

By John Marples , Jan 28, 2023

Folding multihulls and their beam-reduction strategies.

A Farrier 33R trimaran with amas folded and secured on a road-legal trailer exem- plifies the advantages of adjustable- beam multihulls, which are easy to trans- port and store out of the water.

“I’ll be surprised if you can find space in the harbor for that thing,” I heard him say as my new 37 ‘ (11.3m) trimaran was about to be launched. I hadn’t given it much thought, but now this legitimate question was raised, and where to moor was the next issue at hand. Space, particularly width of a slip, becomes the limiting requirement. But then, space also is one of the attractive features of multihulls—deck space to move around on, free from the confines of the cockpit.

Step aboard any multihull and it is obvious how much real estate they offer. Even small models seem expansive. The beam of the typical catamaran is half its length, and trimarans are even wider, sometimes as wide as they are long. Aside from increasing space, beam also boosts stability without adding ballast. The early Pacific Islanders created these form-stable craft for fishing and interisland commerce and voyaging where natural island harbors were few, so the boats had to be light enough for crew to carry them up the beach. Today’s modern multihulls are still lighter than contemporary monohulls, but the larger ones preclude the option of dry sailing them from the beach. They require more marina space than monohulls, and the limited number of slips to accommodate them can be a problem. As someone once put to me, “Multihulls have a poor ‘stacking factor.’”

With catamarans and trimarans becoming more popular, they demand mooring solutions. Some marinas offer shallow-water slips to multihulls, typically at the inboard ends of docks, next to the seawall, because multihulls either have shallow keels or retractable boards. Some marinas also designate the end ties as multihull slips in areas not used for transients. Even though these boats protrude farther into the channel than monohulls, the extra space their beam occupies is relatively small. With multihulls crowding waiting lists for marina slips, builders were prompted to consider folding systems to “improve their stacking factor.”

Without ballast, smaller multihulls up to about 30 ‘ (9.1m) can be dry-stored on a trailer, and most launch ramps easily accommodate over-width boats. If the boat’s beam can be reduced to the legal highway width of 8.5 ‘ (2.6m), the owner can store the boat at home. Today, folding trimarans and catamarans are common sights on trailers in storage yards and backyards. Various folding systems have evolved to support this need, especially for the backyard builder. Some beam-reduction systems allow the boats to be folded and stored in the water in conventional-size marina slips, while other systems facilitate efficient storage or provide street-legal trailering.

Folding Systems

Basic folding systems are separated into several categories:

take-apart akas, the simplest beam-reduction method
telescoping akas (sliding beams)
simple horizontal hinge
complex horizontal hinge systems
vertical hinges (swing wing)
complex swing wing

The following overview of folding systems illustrates how these mechanisms work. It is not intended to be an exhaustive listing of available folding designs. I’ll address two-hull boats (catamarans and proas) first, followed by trimarans. Each type has its challenges and advantages. All are separated into two more categories: transportable boats and trailerable boats. The characteristic distinguishing between them is the time and effort required to launch, starting from an on-the-trailer folded condition. Trailerable implies the possibility of daily launching, requiring less than an hour from trailering to sailing. Transportable denotes a road-legal trailer package but with a longer assembly time to sail away. It might even take more than one trailer load, and considerable assembly time. Legal width in this category could extend to 10 ‘ (3m) wide if OVERSIZE LOAD signs are used (consult local laws). Transportable boats usually require seasonal transport with storage in the water during sailing season and dry storage in the winter. Both categories benefit from the ability to “go to weather at 65 mph” to reach any suitable launching site, even hundreds of miles from home. This opens the possible sailing venue to any water body with a launch ramp and road access, and some trailerable and transportable boats can be delivered anywhere in the world in standard shipping containers.

Catamarans and Proas

The WindRider 17′ trima- ran’s telescoping tubular akas are secured with pins

Hobie Cats and other beach cats are familiar sights around lakes, beaches, and harbors. They are usually built to 8 ‘ (2.4m) beam and do not need folding systems. The 19 ‘ (5.8m) Tornado class catamaran at 10 ‘ wide uses a side tilt-up trailer to reduce beam. Larger catamarans needing folding systems have greater challenges than trimarans of the same length, for a few reasons: The hulls are normally bigger (and heavier) than amas for the same length trimaran; the mast is stepped on the center of an aka, midway between the hulls, which means the aka must be extra strong; and there is no easy means of supporting the hulls while the beam is being expanded to the sailing position, requiring that the trailer have an expanding-beam function. As a result, folding systems are less common on cats and are usually of three types:

folding akas along the centerline or to a center pod
telescoping akas
take-apart akas

On this Wharram cat, the akas are securely lashed into “deck alleys.”

Designers have used telescoping akas, but production boats generally avoid the associated complexity and cost. The mechanically straightforward take-apart feature has successfully been used by many boats, like the 27 ‘ (8.2m) Stiletto Cat and others. Generally, the assembly of these boats takes some time and muscle, which relegates them to the transportable category. Stiletto Cat advertising suggests a four-hour setup time, but in reality, it is much longer. All the James Wharram–designed catamarans up to 63 ‘ (19.2m) are held together with rope lashings and can be dismantled for transport. The required time and effort are generally proportional to the length of the boat.

Note that the Gougeon 32 ‘ (9.7m) sailing catamaran is unique, at 8 ‘ wide, without folding capability but with a water ballast system to make up for the lack of form stability.

The large main hull of a typical smaller trimaran offers a larger interior space than a comparably sized catama ran, a deep footwell in the cockpit for comfortable seating, and a folding system for trailering with the amas connected to a well-supported main hull. In addition, the mast is stepped on the main hull, with the headstay attached to the bow, not to the akas.

Trailerable trimarans come in all sizes to about 32 ‘ long, with transportable designs somewhat longer. The latter types tend to have larger interior spaces and less complex connectives. To a certain extent, manufacturers were willing to add cost to the folding system to reduce setup time. Folding capability on or off the water also adds to the design challenges.

Take-Apart Aka Systems

This is the least expensive method and easiest to achieve for the home builder or the manufacturer. The akas may be built-up wood box beams or tubular metal. Each beam is secured to the hulls by through-bolts, bolted straps, plug-in sockets, or lashings. Tubular aluminum beams are the lightest but most expensive. Regardless of attachment method, the hulls must be supported in their respective positions for the akas to be installed. In small vessels, this can be an abbreviated procedure, but larger vessels will require a special trailer to hold the disconnected amas while on the road.

The Chesapeake Light Craft 15′ single outrigger canoe akas lash into saddles on both hulls.

Telescoping Aka Systems

The telescoping option is limited to boats where the total stack-up width and length dimensions of the hulls and fully retracted akas do not exceed the legal road limits. The WindRider 17 is a good example. The boat is supported on “high bars” on the trailer, leaving the amas free to be moved in or out. The simplicity of the akas and trailer-support system reduces cost and launching time.

In larger vessels, this system has been applied to reduce width for storage in marina slips. For these boats, the sliding system is large and complex, usually requiring some sort of power to make the telescope slide. Because the sliding mechanism requires a small clearance between the sliding members, the akas will move slightly during sailing, which is difficult to avoid.

The 1970s-vintage Telstar 26 features a simple hinge-down system with a bolted con- nection on deck and a bolted strut below.

Simple Horizontal Hinge Systems

Early trailerable trimaran designs often incorporated a simple hinged beam-reduction system to fold both sides down. Boats to about 25 ‘ (7.6m) with a 16 ‘ (4.9m) beam could be made to fold to 8 ‘ . At the ama end, lifting the hull, sometimes with attached wing deck, could require substantial muscle or a mechanical lift. Even for smaller boats this task may be beyond one person’s capability. Normally, bolts and plates between the members secure the hull for sailing. On the Searunner 25 and Constant Camber 26 (7.9m), double-hinged tubes are bolted to tangs on the main hull.

The Searunner 25 trimaran has a hinge mechanism on its metal-tube A-frame akas that secures with bolts at both ends.

Commonly, simple hinge systems require that the main hull be positioned rather high on the trailer so the amas clear the trailer wheels beneath. A disadvantage is that the trailer must be submerged more deeply than usual for the boat to float off. Compared to the Telstar system, the Searunner 25 offered some improvement by positioning the hinge point at the top of the cabinside, raising the folded ama slightly.

Complex Aka Hinge Systems

A complex system for folding multihulls, much like a garage door lift linkage, was developed and patented by Ian Farrier for his trailerable trimaran designs. It allows one person to fold or unfold the boat while it’s afloat. Before launching, the mast is stepped and secured with lower stays. Note that folded storage in the water for long periods is not practical because the immersed ama’s topsides will gather marine fouling. In addition, the arrangement of the support linkage arms has a very shallow angle with the aka, causing them to be highly stressed, which adds significant weight and cost.

Unfolding it requires help from friends.

A complex folding system I developed has only four attachment bolts and a wide-angle strut brace. It is very light but requires folding prior to launching. It relies on a simple roller dolly on a beam attached to the trailer to support the ama during folding and unfolding.

Swing-Wing Systems

In-water storage of folding trimarans is generally limited to swing-wing designs, where the hulls all float on their respective waterlines, either folded or unfolded. Many variations have been used in production boats, and among the most successful is the Quorning-designed Dragonfly. It has hinged arms supported by a “waterstay”— a diagonal cable under the arm to counteract cantilever aka loads. The outer end of the arm, on the ama deck, pivots on a single pin. The waterstay becomes slack when the boat is folded, leaving only the hinge to support the ama in the folded configuration. I’ve seen one folded boat that was damaged while moored at the dock in strong harbor waves when the ama climbed onto the dock. Swing-wing designs stored in the water must provide strong vertical support for the ama in the folded condition

A swing-wing aka system on the Borg Quorning–designed Dragonfly 32 is further supported by a waterstay when rigged for sailing. The akas can be adjusted in and out while in the water and for storage at the dock.

The main challenge of the swing-wing system is to get all the pivot axes parallel because they must rotate about 90° without binding. If there is any depth to the structure, this accuracy is critical, as the pins or pivot axles could be quite long, so even a small inaccuracy will make the system difficult to assemble, let alone pivot smoothly.

Folding Multihulls with Flat Swing-Wing Akas

The most basic swing-wing system is the flat aka configuration developed by Jim Brown. He avoided the need for perfect parallel alignment of all hinge axes because the beams are not very thick, and the pivot-pin holes can have additional clearance. For the swing system to operate without binding, spacing of the pivot points must be identical on all the swing arms. The system’s downside is strength, because the aka must support all the heeling loads in a relatively narrow beam. For some boats, a waterstay may need to be added to increase cantilever strength and reduce deflections when sailing.

The Seaclipper 16 flat swing- wing akas are made from common dimensional lumber and pivot using steel bolts.

A logical improvement in strength for swing arms is to add a truss, with triangulated strength that will easily bear all the heeling loads from the ama. Here again, it is essential that pivot axes be in perfect alignment to avoid binding. To my eye, open trusses in sleek yachts are never beautiful, but they offer higher strength for lower weight.

Complex Swing-Wing Systems

If the akas are not flat along their full length, it is more difficult to achieve a smoothly pivoting system. My latest boat, Syzygy (pronounced, sis-a-gee), is a case in point. Flat akas offer little variation in styling—flat is flat. To add underwing clearance and more attractive aesthetics, many designers favor the arched aka. This configuration allows the aka to approach the ama hull from above and connect through the deck for more usable immersion of the ama buoyancy, and to keep the aka above the wavetops.

This system has arched akas with an upward angle (dihedral) as they extend from the main hull and descend with a smooth curve onto the ama deck. The pivot axis must also be inclined, normal to the surface, to allow it to pivot. To make life simple, the vertical centerline of the ama is inclined inboard at the top by the same amount, which aligns all the pivot axes with the ama vertical centerline. If the beam is level fore-and-aft, when the ama is folded inboard, it is positioned rather low, due to the arch. To compensate, the akas must be given a negative angle of attack to make the folded ama arrive in the same position as a simple flat aka system. It’s a good challenge for any boatbuilder to get it right and a good use of a digital level. The angles in Syzygy were 8° dihedral, and a nega tive 5° angle of attack. The aka pivot surfaces must be perfectly parallel on both ends—at the inboard aka pivots and the ama deck pivot tables.

Jan Gougeon designed and built strings, a 40′ swing-wing catamaran with carbon- tubular-truss swing akas built over foam mandrels.

A late iteration of the Telstar 26 became the Telstar 28 with a vertical-axis swing-wing system. This production boat is no longer manufactured but was unique for its faired wing and attempt to hide the folding system from view. It also featured an electric linear drive to fold/unfold the heavy akas.

For transporting folding multihulls on the highway, road trailers must have some specific attributes to properly support the hulls. Most models use transverse cradle supports under the hull at major interior bulkhead positions. It is important to install bow guides on the trailer to get the hull to settle in exactly the right place when retrieved from the water. Rollers beneath the hull are not recommended, as they tend to distort it and potentially cause damage. The amas require enough support so the folding mechanism is not carrying the load when being towed.

For swing-wing boats, there is a significant change in the center of gravity between folded to unfolded configurations. Normally, the amas swing back when folded and swing forward for the sailing position. If the trailer has the proper tongue weight for towing on the hitch with the boat folded, the weight will increase when unfolded. For trailers with telescoping tongues, tongue design must accomodate that weight; otherwise, the extended tongue may bend severely during launching or retrieval.

Homebuilt wooden trailers are popular for these specialized boats, and some designers provide plans for them. Without much metal in them, they will probably float, which sometimes leads to difficulty at launching. Adding some steel channel to the bunks can solve that. However, floating is not an undesirable feature if a trailer floats level but is submerged enough to maneuver the hull into the bunks, and the hull settles into the right place automatically. Floating trailers also never run off the end of the ramp.

Conclusions

There’s truth in the humorous claim that “the new family yacht has to look good behind your SUV.” But while many of the latest small boats are daysailers, folding multihulls have expanded the trailerable and transportable boat size to include those with weekend cruising capability, up to about 32 ‘ . As we’ve seen, those essential folding or retraction mechanisms are not simple and must be carefully designed and engineered, even by the home builder. But for owners of these boats, seasonal storage and slip availability are no longer problems. And the overall reduction in total cost can bring owning a boat within reach for many more people. What’s not to like about that?

About the Author: John Marples has designed, built, and rigged many sail- ing vessels. His portfolio includes doz- ens of wood-epoxy composite sailing and power multihulls to 110′ (33.5m). He operates Marples Marine , a multihull design and engineering firm in Penobscot, Maine

Dieter Loibner | Professional BoatBuilder Magazine

Nomenclature

Multihull designers have developed some useful, specific names for components, mostly derived from the Pacific Islander language.

Aka (ah-kah) refers to the crossbeam structure of any multihull. Designers used to call them “cross-beams,” but writing that on hand-drawn plans took up too much space and time, so this shorter Polynesian name became the standard.

Ama (ah-mah) is the Polynesian name for the outer hull of a trimaran or proa. They were formerly named “floats” or “outer hulls” (never pontoons), but again, ama is shorter.

Vaka (vah-kah) is the Polynesian name for the main (largest) hull of a trimaran or proa. Since it can be confused with the other names and is not very descriptive, most designers have opted for the term main hull.

Waterstay is a diagonal stay, metal or synthetic rope, below the aka, between the main hull near the waterline and aka near its outboard end. This stay counteracts the upward load from ama buoyancy when the ama is immersed.

—John Marples

The Crossbeam (Aka) Structure

T he essential function of any crossbeam (aka) system on a multihull is to structurally connect the hulls in a way that resists all the forces generated when sailing. Heeling forces from lift on the sails must be transferred to the leeward hull by the aka structure. The forces on the akas are complex, composed of cantilever bending due to heeling loads, twisting of the structural platform, and horizontal bending caused by drag from the ama’s forward motion through the water. The heeling force, resisted by the buoyancy of the ama, pushes up, causing cantilever bending loads in the akas similar to the forces on an airplane wing. Torsion is created when the sails’ lift pushes the leeward ama bow down, while the shrouds supporting the mast pull the weather-side ama stern up. Drag from the leeward ama tries to bend the akas toward the stern, and forces from the windward shroud tend to pull the aka forward as well as up. These forces all act together at the attachment points on the hulls. In most cases, torsion is resisted by the tubular hull and cabin structure itself. Heeling is countered by the cantilever strength of the aka beams and is sometimes strengthened by diagonal waterstay cables beneath. Drag forces can be resolved by the fore-and-aft strength of the akas or by adding diagonal cables between the akas. Each folding system must accommodate these loads through all the pivoting components in the structure.

Of key interest in aka design are the loads imposed on the ama hulls by the seaway when sailing to windward. These hulls are subject to significant loads on the outboard sides. The windward ama is pummeled by wavetops, and the leeward ama is pushed sideways due to leeway. Since the aka system is characteristically attached through the ama deck, these forces are trying to rotate the ama keel inboard, toward the main hull, in either case. The same is true for catamarans, concerning the aka loads where they emerge at the hull inboard sides. These loads can be calculated to estimate the strength required for any configuration and should be part of the design’s stress analysis. If centerboards or daggerboards are located in the amas, those rotating forces are significantly increased.

Of further interest in swing-wing designs is the clearance between pins and brackets in vertical pivot mechanisms. When sailing, the forces at the hinge pins can change from positive to negative repetitively, creating noise and wear. The wear will eventually elongate the holes, reduce pin diameter, and become a maintenance problem. Designs like the flat wing can be tightened to eliminate movement, which will eliminate wear. Amas with waterstays tend to put the akas in compression and stop the vertical deflection that would be normally carried through the hinge pins. In that case, the pins would be loaded in only one direction and not be subject to cyclic ± loads. —J.M.

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Polynesian multihull terminology

Polynesian multihull terminology explained

Polynesian multihull terminology , such as "ama", "aka" and "vaka" (or "waka") are multihull terms that have been widely adopted beyond the South Pacific where these terms originated. This Polynesian terminology is in common use in the Americas and the Pacific but is almost unknown in Europe, where the Anglo-Saxon terms "hull" and "outrigger" form normal parlance. Outriggers, catamaran s, and outrigger boat s are a common heritage of all Austronesian peoples and predate the Micronesian and Polynesian expansion into the Pacific. They are also the dominant forms of traditional ships in Island Southeast Asia n and Malagasy Austronesian cultures, where local terms are used. [1] [2]

See also: Waka (canoe) and Outrigger boat . The term vaka or waka means "boat" or "canoe" in most Polynesian languages. It comes from Proto-Austronesian *abaŋ, meaning "ship" or "canoe". Cognate s in other Austronesian languages include Ivatan Awang , Tagalog and Visayan bangka , Malay wangkang , and Fijian waqa . [3]

"Ama", "aka" and "vaka"

The term ama is a word in the Polynesian and Micronesian languages to describe the outrigger part of a canoe to provide stability. Today, among the various Polynesian countries, the word ama is often used together with the word vaka ( Cook Islands ) or waka ( Māori ) or va'a ( Samoa Islands , Tahiti ), cognate words in various Polynesian languages to describe a canoe.

The Polynesian term vaka is the main hull , the ama is the outrigger, and the aka or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimaran s.

In modern sailing, the term is sometimes used to refer to the outrigger on double-outrigger canoes ( trimaran s), or the two sections of a catamaran . However, calling the two sections of a catamaran by the word ama is not technically correct since they are of equal size. A catamaran is technically a wa'a wa'a or double canoe connected by an aka . [4]

On a proa, the ama may provide lift or ballast , depending on whether it is designed to be used to leeward or windward ; on a trimaran it is designed primarily to provide lift. There are many shapes of ama; those used in proa s are generally laterally symmetric, as the proa is designed to sail with either end forwards, while trimaran ama are one-directional and may have no axis of symmetry.

The most advanced ama are composed of highly curved surfaces that generate lift when driven forward through the water, much like an airplane wing. This lift may be directed to the windward, used to counter slipping to leeward , or may be oriented vertically to counter heeling forces from the sailing rig. These highly curved structures are much more difficult to manufacture than traditional ama and are therefore more expensive. The Bruce foil is an example of a type of leeboard often attached to an ama to assist in producing lift.

Use of the term in other cultures

Even though double-outrigger ships ( trimaran s, sometimes informally referred to as "proas" historically) of other related Austronesian groups in Island Southeast Asia , Island Melanesia , and Madagascar didn't reach Polynesia or Micronesia, they may also sometimes use Polynesian terminology in modern times, especially when used in sport sailing. [5]

The US Navy tri-hull Independence -class littoral combat ship refers to their outboard hull sections as an "Amah". "An Amah tip is the leading edge of the all-aluminum, trimaran-type vessel’s outrigger, or amah, and is more than seven feet across and weighs 850 pounds." [6]

Polynesian navigation
Bangka (boat)
Waka (canoe)
Outrigger canoe
Hōkūleʻa
Beheim . B. A. . Bell . A. V. . Inheritance, ecology and the evolution of the canoes of east Oceania . Proceedings of the Royal Society B: Biological Sciences . 23 February 2011 . 278 . 1721 . 3089–3095 . 10.1098/rspb.2011.0060. 21345865 . 3158936 .
Hornell . James . Was the Double-Outrigger Known in Polynesia and Micronesia? A Critical Study . The Journal of the Polynesian Society . 1932 . 41 . 2 (162) . 131–143.
Dempwolff . Otto . Vergleichende Lautlehre des austronesischen Wortschatzes . Zeitschrift für Eingeborenen-Sprachen . 1934–1938 . Special Publication . 15,17,19.
Web site: Story: Canoe navigation - Waka – canoes' . Rāwiri Taonui, Te Ara . The Encyclopedia of New Zealand . 4 March 2009.
Web site: The Tridarka Raider . 2007-10-30. https://web.archive.org/web/20071020045916/http://www.tridarkaraider.com/. 20 October 2007. dead.
Alcoa Provides Aluminum Amah Tips to Austal for Littoral Combat Ship USS Jackson (LCS 6) . 16 April 2012 .

This article is licensed under the GNU Free Documentation License . It uses material from the Wikipedia article " Polynesian multihull terminology ".

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Multihull Capsize Risk Check

Waves, squalls, and inattention to trim and helm contribute to instability..

In recent years we’ve seen a surge in interest in multihulls. Thirty years ago, when my experience with cruising multihulls began, nearly all of the skippers served an apprenticeship with beach cats, learning their quirks by the seat of their pants. They hiked out on trapezes and flew head-over-heels past their pitch-pole prone Hobie 16s, until they learned the importance of keeping weight way aft on a reach and bearing off when the lee bow began to porpoise.

By contrast, the new generation of big cat buyers skipped this learning process, learning on monohulls or even choosing a big stable cat as their first boat. Heck, nobody even builds real beach cats anymore, only pumped up racing machines and rotomolded resort toys. So we’re guessing there are a few things these first-time cruising multihull sailors don’t know, even if they have sailed cruising cats before.

It is extremely hard to capsize a modern cruising cat. Either a basic disregard for seamanship or extreme weather is required. But no matter what the salesman tells you (“none of our boats have ever …”), it can happen. A strong gust with sail up or a breaking wave in a survival storm can do it. And when a multihull goes over, they don’t come back.

Trimarans tend to be more performance oriented than catamarans. In part, this is because it’s easier to design a folding trimaran, and as a result Farrier, Corsair, and Dragonfly trimarans had a disproportionate share of the market.

In spite of this and in spite of the fact that many are raced aggressively in windy conditions, capsizes are few, certainly fewer than in equivalent performance catamaran classes. But when they do go over, they do so in different ways.

Trimarans have greater beam than catamarans, making them considerably more resistant to capsize by wind alone, whether gusts or sustained wind. They heel sooner and more than catamaran, giving more warning that they are over powered.

Waves are a different matter. The amas are generally much finer, designed for low resistance when sailing deeply immersed to windward. As a result, trimarans are more susceptible to broach and capsize when broad reaching at high speed or when caught on the beam by a large breaking wave.

In the first case, the boat is sailing fast and overtaking waves. You surf down a nice steep one, into the backside of the next one, the ama buries up to the beam and the boat slows down. The apparent wind increases, the following wave lifts the transom, and the boat slews into a broach. If all sail is instantly eased, the boat will generally come back down, even from scary levels of heel, but not always.

In the second case a large wave breaks under the boat, pulling the leeward ama down and rolling the boat. Catamarans, on the other hand, are more likely to slide sideways when hit by a breaking wave, particularly if the keels are shallow (or raised in the case of daggerboards), because the hulls are too big to be forced under. They simply get dragged to leeward, alerting the crew that it is time to start bearing off the wind.

Another place the numbers leave us short is ama design. In the 70s and 80s, most catamarans were designed with considerable flare in the bow, like other boats of the period. This will keep the bow from burying, right? Nope. When a hull is skinny it can always be driven through a wave, and wide flare causes a rapid increase in drag once submerged, causing the boat to slow and possibly pitchpole.

Hobie Cat sailors know this well. More modern designs either eliminate or minimize this flare, making for more predictable behavior in rough conditions. A classic case is the evolution of Ian Farrier’s designs from bows that flare above the waterline to a wave-piercing shape with little flare, no deck flange, increased forward volume, and reduced rocker (see photos page 18). After more than two decades of designing multihulls, Farrier saw clear advantages of the new bow form. The F-22 is a little faster, but more importantly, it is less prone to broach or pitchpole, allowing it to be driven harder.

Beam and Stability

The stability index goes up with beam. Why isn’t more beam always better? Because as beam increases, a pitchpole off the wind becomes more likely, both under sail and under bare poles. (The optimum length-to-beam ratios is 1.7:1 – 2.2:1 for cats and 1.2:1-1.8:1 for trimarans.) Again, hull shape and buoyancy also play critical roles in averting a pitchpole, so beam alone shouldn’t be regarded as a determining factor.

Drogues and Chutes

While monohull sailors circle the globe without ever needing their drogues and sea anchors, multihulls are more likely to use them. In part, this is because strategies such as heaving to and lying a hull don’t work for multihulls. Moderate beam seas cause an uncomfortable snap-roll, and sailing or laying ahull in a multihull is poor seamanship in beam seas.

Fortunately, drogues work better with multihulls. The boats are lighter, reducing loads. They rise over the waves, like a raft. Dangerous surfing, and the risk of pitchpole and broach that comes with it, is eliminated. There’s no deep keel to trip over to the side and the broad beam increases the lever arm, reducing yawing to a bare minimum.

Speed-limiting drogues are often used by delivery skippers simply to ease the motion and take some work off the autopilot. By keeping her head down, a wind-only capsize becomes extremely unlikely, and rolling stops, making for an easy ride. A properly sized drogue will keep her moving at 4-6 knots, but will not allow surfing, and by extension, pitch poling.

For more information on speed limiting drogues, see “ How Much Drag is a Drogue? ” PS , September 2016.

Capsize Case Studies

Knock wood, we’ve never capsized a cruising multihull (beach cat—plenty of times), but we have pushed them to the edge of the envelope, watched bows bury, and flown multi-ton hulls to see just how the boat liked it and how fast she would go. We’re going to tell you about these experiences and what can be learned from them, so you don’t have to try it.

First, it helps to examine a few examples of some big multihull capsizes.

Techtronics 35 catamaran, John Shuttleworth design

This dramatic pitchpole occurred in a strong breeze some 30 years ago. In order to combine both great speed and reasonable accommodation, the designer incorporated considerable flare just above the waterline, resulting in hulls that were skinny and efficient in most conditions, but wide when driven under water in steep chop.

The boat was sailing fast near Nova Scotia, regularly overtaking waves. The bows plowed into a backside of a particularly steep wave, the submerged drag was huge, and the boat stopped on a dime. At the same time, the apparent wind went from about 15 knots into the high 20s, tripling the force on the sails and rapidly lifting the stern over the bow. Some crew were injured, but they all survived.

PDQ 32 Catamaran

On July 4, 2010, the boat’s new owners had scheduled time to deliver their new-to-them boat up the northern California coast. A strong gale was predicted, but against all advice, they left anyway. The boat turned sideways to the confused seas and a breaking wave on the beam capsized the boat. There were no injuries, and the boat was recovered with only moderate damage a few weeks later. Repaired, she is still sailing.

Another PDQ 32 was capsized in the Virgin Islands when a solo sailor went below to tend to something and sailed out of the lee of the island and into a reinforced trade wind.

Sustaining speed with wider tacking angles will help overcome leeway.

Cruising cats can’t go to windward. That’s the rumor, and there’s a kernel of truth to it. Most lack deep keels or dagger boards and ex-charter cats are tragically under canvassed for lighter wind areas, a nod to near universal lack of multihull experience among charter skippers. Gotta keep them safe. But there are a few tricks that make the worst pig passable and the better cats downright weatherly. Those of you that learned your craft racing Hobies and Prindles know most of this stuff, but for the rest of you cruising cat sailors, there’s some stuff the owner’s manual leaves out.

“Tune” the Mast

Having no backstay means that the forestay cannot be kept tight unless you want to turn your boat into a banana and over stress the cap shrouds. Although the spreaders are swept back, they are designed primarily for side force with just a bit of pull on the forestay. The real forestay tension comes from mainsheet tension.

Why is it so important to keep the forestay stay tight? Leeward sag forces cloth into the luff of the genoa, making it fuller and blunting the entry into the wind. The draft moves aft, the slot is pinched, and aerodynamic drag increases. Even worse, leeway (sideslip) increases, further increasing drag and sliding you away from your destination. Sailing a cruising cat to windward is about fine tuning the lift to drag ratio, not just finding more power.

How do you avoid easing the mainsheet in strong winds? First, ease the traveler instead. To avoid pinching the slot, keep the main outhaul tight to flatten the lower portion of the main. Use a smaller jib or roll up some genoa; overlap closes the slot. Reef if need be; it is better to keep a smaller mainsail tight than to drag a loose mainsail upwind, with the resultant loose forestay and clogged slot. You will see monos with the main twisted off in a blow. Ignore them, they are not cruising cats. It is also physically much easier to play the traveler than the main sheet. Be glad you have a wide one.

Check Sheeting Angles

Very likely you do not have enough keel area to support large headsails. As a result, you don’t want the tight genoa lead angles of a deep keeled monohull. All you’ll do is sail sideways. Too loose, on the other hand, and you can’t point. In general, 7-10 degrees is discussed for monos that want to pinch up to 40 degrees true, but 14-16 degrees makes more sense for cruising cats that will sail at no less than 50 degrees true. Rig up some temporary barber haulers and experiment. Then install a permanent Barber-hauler; see “ Try a Barber Hauler for Better Sail Trim ,” Practical Sailor , September 2019.

The result will be slightly wider tacking angles, perhaps 105 degrees including leeway, but this will be faster for you. You don’t have the same hull speed limit, so let that work for you. Just don’t get tempted off onto a reach; you need to steer with the jib not far from luffing.

Watch the fore/aft lead position as well. You want the jib to twist off to match the main. Typically it should be right on the spreaders, but that depends on the spreaders. If you have aft swept shrouds, you may need to roll up a little genoa, to 110% max.

Use your Tell-Tales

On the jib there can be tell-tale ribbons all over, but on the main the only ones that count are on the leech. Keep all but the top one streaming aft. Telltales on the body of sail are confused by either mast turbulence (windward side) or pasted down by jib flow (leeward side) and won’t tell you much. But if the leach telltales suck around to leeward you are over sheeted.

Keep Your Bottom Clean

It’s not just about speed, it’s also pointing angle. Anything that robs speed also makes you go sideways, since with less flow over the foil there will be less lift. Flow over the foils themselves will be turbulent. Nothing slows you down like a dirty bottom.

Reef Wisdom

Push hard, but reef when you need to. You will have the greatest lift vs. windage ratio when you are driving hard. That said, it’s smart to reef most cruising cats well before they lift a hull to avoid overloading the keels. If you are feathering in the lulls or allowing sails to twist off, it’s time to reef.

Don’t Pinch

Pinching (pointing to high) doesn’t work for cats. Get them moving, let the helm get a little lighter (the result of good flow over the rudder and keel), and then head up until the feeling begins to falter. How do you know when it’s right? Experiment with tacking angles (GPS not compass, because you want to include leeway in your figuring) and speed until the pair feel optimized. With a genoa and full main trimmed in well, inside tracks and modified keels, and relatively smooth water, our test PDQ can tack through 100 degrees with the boat on autopilot. Hand steering can do a little better, though it’s not actually faster to windward. If we reef or use the self-tacking jib, that might open up to 110-115 degrees, depending on wave conditions. Reefing the main works better than rolling up jib.

Boats with daggerboards or centerboards. The comments about keeping a tight forestay and importance of a clean bottom are universal. But the reduction in leeway will allow you to point up a little higher, as high as monohulls if you want to. But if you point as high as you can, you won’t go any faster than similar monohulls, and quite probably slower. As a general rule, tacking through less than 90 degrees, even though possible, is not the best strategy. A slightly wider angle, such as 100 degrees, will give a big jump in boat speed with very little leeway.

Chris White Custom 57

In November 2016, winds had been blowing 25-30 knots in stormy conditions about 400 miles north of the Dominican Republic. The main had two reefs in, and the boat was reaching under control at moderate speed when a microburst hit, causing the boat to capsize on its beam. There were no serious injuries.

Another Chris White 57 capsized on July 31, 2010. It had been blowing 18-20 knots and the main had a single reef. The autopilot steered. The wind jumped to 62 knots in a squall and changed direction so quickly that no autopilot could be expected to correct in time.

Gemini 105mC

In 2018, the 34-foot catamaran was sailing in the Gulf of Mexico under full sail at about 6 knots in a 10-15 knot breeze. Squalls had been reported on the VHF. The crew could see a squall line, and decided to run for cover. Before they could get the sails down, the gust front hit, the wind shifted 180 degrees, and the boat quickly went over.

38-foot Roger Simpson Design

The catamaran Ramtha was hit head-on by the infamous Queen’s Birthday storm in 1994. The mainsail was blown out, and steering was lost. Lacking any control the crew was taken off the boat, and the boat was recovered basically unharmed 2 weeks later. A Catalac catamaran caught in the same storm trailed a drogue and came through unharmed. Of the eight vessels that called for help, two were multihulls. Twenty-one sailors were rescued, three aboard the monohull Quartermaster were lost at sea.

15 meter Marsaudon Ts

Hallucine capsized off Portugal on November 11 of this year. This is a high performance cat, in the same general category as the familiar Gunboat series. It was well reefed and the winds were only 16-20 knots. According to crew, it struck a submerged object, and the sudden deceleration caused the boat to capsize.

Multihulls We’ve Sailed

Clearly seamanship is a factor in all of our the previous examples. The watch needs to be vigilant and active. Keeping up any sail during squally weather can be risky. Even in the generally benign tropics, nature quickly can whip up a fury. But it is also true that design choices can impact risk of capsize. Let’s see what the numbers can tell us, and what requires a deeper look.

Stiletto Catamaran

We’ve experienced a number of capsizes both racing and while driving hard in these popular 23-foot catamarans. The combination of light displacement and full bow sections make pitchpoling unlikely, and the result is very high speed potential when broad reaching. Unfortunately, a narrow beam, light weight, and powerful rig result in a low stability factor. The potential for capsize is real when too much sail is up and apparent wind is directly on the beam. The boat can lift a hull in 12 knots true. This makes for exciting sailing when you bring your A-game, but limits the boat to coastal sailing.

Corsair F-24 MK I trimaran

Small and well canvased, these boats can capsize if driven hard (which they often are), but they are broad beamed, short-masted, and designed for windy sailing areas. F-24s are slower off wind than the Stiletto, in part because of greater weight and reduced sail area, but also because the main hull has more rocker and does not plane as well. They are faster to weather and point considerably higher than a Stiletto (90-degree tacking angle vs. 110 degrees). This is the result of greater beam, a more efficient centerboard design, and slender amas that are easily driven in displacement mode. The boat is quite forgiving if reefed.

Going purely by the numbers, this boat seems nearly identical to the F-24. In practice, they sail quite differently. The Dash uses a dagger board instead of centerboard, which is both more hydrodynamic and faster, but more vulnerable to damage if grounded at high speed.

The rotating mast adds power that is not reflected in the numbers. The bridgedeck clearance is higher above the waterline, reducing water drag from wave strikes. The wave-piercing amas create greater stability up wind and off the wind. The result is a boat that is slightly faster than the original F-24 and can be driven much harder off the wind without fear of pitchpole or broach.

Without proper testing, calculating stability yields only a rough picture.

Evaluating multihull performance based on design numbers is a bit more complicated than it is with ballasted, displacement monohulls, whose speed is generally limited by hull form. [Editor’s note: The formula for Performance Index, PI has been updated from the one that originally appeared in the February 2021 issue of Practical Sailor.

The following definitions of units apply to the adjacent table:

SA = sail area in square feet

D (displacement) = weight in pounds

LWL = length of waterline in feet

HCOE = height of sail center of effort above the waterline in feet

B = beam in feet

BCL = beam at the centerline of the hulls in feet.

Since a multihull pivots around the centerline beam, the overall beam is off the point and is not used in formulas. Calculate by subtracting the individual hull beam from the overall beam.

SD ratio = SA/(D/64)^0.66

This ratio gives a measure of relative speed potential on flat water for monohulls, but it doesn’t really work for multihulls.

Bruce number = (SA)^0.5/(D)^0.333

Basically this is the SD ratio for multihulls, it gives a better fit.

Performance index = (SA/HCOE)^0.5 x (D/1000)^0.166

By including the height of the COE and displacement, this ratio reflects the ability of the boat to use that power to sail fast, but it understates the importance of stability to the cruiser.

Stability factor = 9.8*((0.5*BCL*D)/(SA*HCOE))^0.5

This approximates the wind strength in knots required to lift a hull and includes a 40% gust factor. In the adjacent data sheet, we compare the formula’s predicted stability to observed behavior. Based on our experience on the boats represented, the results are roughly accurate.

Ama buoyancy = expressed as a % of total displacement.

Look for ama buoyancy greater than 150% of displacement, and 200 is better. Some early trimaran designs had less than 100 percent buoyancy and would capsize well before flying the center hull. They exhibited high submerged drag when pressed hard and were prone to capsize in breaking waves.

Modern tris have ama buoyancy between 150 and 200 percent of displacement and can fly the center hull, though even racing boats try to keep the center hull still touching. In addition, as a trimaran heels, the downward pressure of wind on the sail increases, increasing the risk of capsize. The initial heel on a trimaran is more than it is on catamarans, and all of that downward force pushes the ama even deeper in the water. Thus, like monohulls, it usually makes sense to keep heel moderate.

These numbers can only be used to predict the rough characteristics of a boat and must be supplemented by experience.

This is the first real cruising multihull in our lineup. A few have capsized. One was the result of the skipper pushing too hard in very gusty conditions with no one on watch. The other occurred when a crew unfamiliar with the boat ignored local wisdom and set sail into near gale conditions.

Although the speed potential of the PDQ 32 and the F-24 are very similar, and the stability index is not very different, the feel in rough conditions is more stable, the result of much greater weight and fuller hull sections.

Like most cruising cats, the PDQs hulls are relatively full in order to provide accommodation space, and as a result, driving them under is difficult. The increased weight slows the motion and damps the impact of gusts. Yes, you can fly a hull in about 25 knots apparent wind (we proved this during testing on flat water with steady winds), and she’ll go 8-9 knots to weather doing it, but this is not something you should ever do with a cruising cat.

Stability by the Numbers

The “stability factor” in the table above (row 14) is based on flatwater conditions, and ignores two additional factors. Unlike monohulls, the wind will press on the underside of the bridgedeck of a multihull once it passes about 25 degrees of heel, pushing it up and over. This can happen quite suddenly when the boat flies off a wave and the underside is suddenly exposed to wind blowing up the slope of the wave. A breaking wave also adds rotational momentum, pitching the windward hull upwards.

Multihulls by the Numbers

Autopilot is a common thread in many capsizes. The gust “came out of no place…” No it didn’t. A beach cat sailor never trusts gusty winds. The autopilot should be disengaged windspeeds and a constant sheet watch is mandatory when gusts reach 30-40 percent of those required to fly a hull, and even sooner if there are tall clouds in the neighborhood. Reef early if a helm watch is too much trouble.

“But surely the sails will blow first, before the boat can capsize?” That would be an expensive lesson, but more to the point, history tells us that well-built sails won’t blow.

“Surely the rig will fail before I can lift a hull?” Again, that could only be the result of appallingly poor design, since a rig that weak will not last offshore and could not be depended on in a storm. Furthermore, good seamanship requires that you be able to put the full power of the rig to work if beating off a lee shore becomes necessary.

Keeping both hulls in the water is up to you. Fortunately, under bare poles and on relatively flat water even smaller cruising cats can take 70 knots on the beam without lifting … but we don’t set out to test that theory, because once it blows for a while over even 40 knots, the real risk is waves.

Everything critical to safety in a blow we learned on beach cats. Like riding a bike, or—better yet—riding a bike off-road, there are lessons learned the hard way, and those lessons stay learned. If you’ve been launched into a pitchpole a few times, the feeling you get just before things go wrong becomes ingrained.

Perhaps you are of a mature age and believe you monohull skills are more than enough to see you through. If you never sail aggressively or get caught in serious weather, you’re probably right.

However, if there’s a cruising cat in your future, a season spent dialing in a beach cat will be time well spent. Certainly, such experience should be a prerequisite for anyone buying a performance multihull. The statement might be a little pointed, but it just makes sense.

Capsize by Wind Alone

Capsizing by wind alone is uncommon on cruising multihulls. Occasionally a performance boat will go over in squally weather. The crew could easily have reefed down or gone to bare poles, but they clung to the idea that they are a sail boat, and a big cat feels so stable under sail—right up until a hull lifts.

Because a multihull cannot risk a knockdown (since that is a capsize), if a squall line is tall and dark, the smart multihull sailors drops all sail. Yes, you could feather up wind, but if the wind shifts suddenly, as gusts often do, the boat may not turn fast enough. Off the wind, few multihulls that can take a violent microburst and not risk a pitchpole. When a squall threatens, why risk a torn sail for a few moments of fast sailing?

You can’t go by angle of heel alone because of wave action. Cat instability begins with the position of the windward hull. Is it flying off waves?

A trimaran’s telltale is submersion of leeward ama. Is the leeward ama more than 30-40 percent under water? The maximum righting angles is a 12-15 degrees for cats and 25-30 degrees for trimarans, but that is on flat water. Once the weather is up, observation of motion becomes far more important. Is the boat falling into a deep trough, or is at about to launch off a steep wave and fly?

Just as monohulls can surprise a new sailor by rounding up and broaching in a breeze, multihulls have a few odd habits that only present themselves just before things go wrong. Excuse the repetition, but the best way to learn to instinctively recognize these signs is by sailing small multihulls.

Sailing Windward

Because of the great beam, instead of developing weather helm as they begin to fly a hull, multihulls can suddenly develop lee helm, causing the boat to bear away and power up at the worst possible moment. This is because the center of drag moves to the lee hull, while the center of drive remains in the center, causing the boat to bear away.

If the boat is a trimaran, with only a center rudder, this rounding up occurs just as steering goes away. This video of a MOD 70 capsize shows how subtle the early warning signs can be ( www.youtube.com/watch?v=CI2iIY61Lc8 ).

Sailing Downwind

Off the wind, the effect can be the reverse. The lee hull begins to bury, and you decide it is time to bear off, but the submerged lee bow acts like a forward rudder. It moves the center of effort far forward and prevents any turn to leeward. Nearly all trimarans will do this, because the amas are so fine. The solution is to bear away early, before the ama buries—or better yet, to reef.

Conclusions

We’re not trying to scare you off multi-hulls. Far from it. As you can probably tell, I am truly addicted. Modern designs have well-established reputation seaworthiness.

But multihull seaworthiness and seamanship are different from monohulls, and some of those differences are only apparent when you press the boat very hard, harder than will ever experience in normal weather and outside of hard racing. These subtle differences have caught experienced sailors by surprise, especially if their prior experience involved only monohulls or cruising multihulls that were never pressed to the limit.

Although the numbers only tell part of the story, pay attention to a boat’s stability index. You really don’t want an offshore cruising boat that needs to be reefed below 22-25 knots apparent. Faster boats can be enjoyable, but they require earlier reefing and a more active sailing style.

When squalls threaten or the waves get big, take the appropriate actions and take them early, understanding that things happen faster. And don’t forget: knockdowns are not recoverable. It is satisfying to have a boat that has a liferaft-like stability, as long as you understand how to use it.

Technical Editor Drew Frye is the author of “Rigging Modern Anchors.” He blogs at www.blogspot/sail-delmarva.com

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The complete list of trimarans.

There is no single trimaran that is best for everyone. Where some prefer luxury cruisers for long trips with family and friends, others might opt for a high performance racing tri for thrilling rides at breakneck speeds. With the recent spike in trimaran popularity, these days there is a perfect tri for every sailor. So to help prospective trimaran owners decide which boat is just right for them, we here at WindRider have put together a comprehensive list of the best trimarans on the market today! Read through for simple at-a-glance trimaran comparisons of boats both big and small, exhilarating and relaxing, and for all price points.

Jump to a specific sailing trimaran: Neel Weta Corsair WindRider Dragonfly Catri Astus Hobie Sea Pearl Farrier Sea Cart Multi 23 Triak SeaRail Warren Lightcraft Diam Radikal Challenger

Known for their award-winning luxury trimarans, NEEL is based in La Rochelle, the capital city of sailing in France. NEEL trimarans are built for fast cruising with an average cruising speed of about 10 knots, and are even configured to facilitate that sustained speed under motor propulsion. The NEEL 45 was notably named Cruising World’s Most Innovative Vessel in 2013, and by all accounts is an easy-to-sail, high performance boat that is just plain fun.

At a glance:

Models: NEEL 45, 65

Length: 45’ – 65’

Cost: $$$$$

Use: Luxury cruiser

A fan favorite, Weta trimarans are fast, stable, and remarkably easy to rig. This single-sailor tri has a capacity of up to three, and the ease with which it can be transported and stored makes this a great, versatile boat for beginners. The Weta was named Sailing World’s 2010 Boat of the Year, and one ride is enough to know why: simply put, the Weta is an absolute ton of fun to sail regardless of skill level.

Models: Weta

Length: 14’5”

Cost: $$ $$$

The high-end Corsair trimaran definitely holds its own in the categories of versatility, performance, and convenience. Boasting a rigging time of 30 minutes from trailer to sailor , the Corsair 42 – whose convenient folding amas makes trailering possible – is a simple option even for single sailors, though cabin space is suitable for two adults. These boats are wicked fast, capable of reaching speeds of 20+ knots, and were made for skilled sailors seeking solid construction and high performance vessels, not for beginners.

Models: Pulse 600, Sprint 750 MKII, Dash 750 MKII, Corsair 28, Cruze 970, Corsair 37, Corsair 42

Length: 19’8” – 37’

Cost: $$$$ $

Use: Sports cruisers

Built for the sailor who wants to maximize the joys of sailing while minimizing any hassle, WindRider trimarans are notoriously fast, very safe, and a blast to sail from start to finish. With several models that can hold between 1 and 6 riders, including adaptive designs to allow participation from sailors of all levels of mobility, there’s something to suit every sailor’s needs. The WindRider 17, an exhilarating ride perfect for families or camper sailors, has been known to reach speeds of up to 20mph. This easy day sailor goes from trailer to sailing in under 30 minutes and is sure to fit in perfectly with whatever adventures you have planned.

Models: WR 16, 17, Tango, Rave V

Length: 10’11” – 18’3”

Cost: $ $$$$

Use: Day sailor

The Danish-built Dragonfly trimarans come in a variety of models ranging from 25’ – 35’, all known for their spry performance, comfortable ride, and ease of use. Every model comes equipped with the unique “SwingWing” feature, a motorized system that can unfold the amas even while the boat is already underway – making it accessible to marinas and slips, and even makes trailering possible. Perfect for those who don’t want to sacrifice their comfort for high performance, the Dragonfly can breeze along at 13 knots while remaining one of the quietest compact cruisers out there.

Models: Dragonfly 25, 28, 32, 35, 1200

Length: 25’ – 39’

Designed for both safe cruising as well as for high speed racing, Catri trimarans will make your day. Especially noteworthy is the Catri 25, a stable yet wildly fast foiling trimaran with accommodations for up to 6 people. With profiles optimized for speeds of 25+ knots when foiling, this is no beginner’s sailboat. The special attention paid to stability in the foil design allows the Catri to be a single sailor vessel, even at foiling speed, with no special physical abilities. Whether you’re taking a small crew for longer rides at shuddering speeds or bringing the whole family along for a shorter, but still thrilling sail, the Catri is truly one of a kind.

Models: Catri 25

Length: 25’

Use: Cruiser/racer

A popular brand of trimaran in Europe, Astus has recently made its way to the US market to the delight of sailors on this side of the pond. Designed to offer maximum pleasure with minimum hassle, all models of Astus trimarans are fast to set up, quick on the water, inherently stable, and always a joy to sail. Their outriggers are mounted on telescopic tubes for easy stowage and towing, and can even be extended and retracted on the water for access to narrow passageways and monohull slips in marinas. With models in all sizes and price points, Astus trimarans are a great option for any sailor.

Models: Astus 16.5, 18.2, 20.2, 22, 24

Cabin: Some models

Length: 16’ – 24’

Use: Sport cruisers

HOBIE ADVENTURE ISLAND

Great for beginners and adventurers alike, the Hobie Mirage Adventure Island series is nothing if not just plain fun. With the option to use as a kayak or as a very basic trimaran, the Hobie is transportable, versatile, unintimidating, lightweight, and wonderfully affordable. The pedal system known as “Mirage Drive” allows a person to pedal the kayak using their legs for an extra kick of movement in slow winds. Amas tuck close to the main hull for docking or car-topping, adding serious ease and convenience to the exhilarating experience of the Hobie.

Models: Hobie Mirage Adventure Island, Mirage Tandem Island

Length: 16’7” – 18’6”

Use: Convertible kayak/trimarans

Best known for its use in camp cruising excursions, the Sea Pearl offers a roomy main hull and particular ability to sail in very shallow waters, making beaching and launching a breeze. The lightweight Sea Pearl trimaran is easy to tow, and the larger-than-expected cabin opens this vessel up for overnight adventures with plenty of storage space. The simple design makes the Sea Pearl notoriously low maintenance, and the ease it takes to rig and sail it add to the overall delight of owning this boat.

Models: Sea Pearl

Length: 21’

Use: Camper cruiser

Quick, lightweight, roomy, and trailerable, Farrier trimarans are made for versatility to fit every sailor’s needs. Different Farrier models are available in plan or kit boat form for those who appreciate building their boat themselves, but of course, also as the full production sail-away boat for the rest of us. Single-handed rigging and launching takes under 10 minutes from start to finish, minimizing hassle and getting you on the water fast. All non-racing Farrier designs use a minimum wind capsize speed of 30 knots or more to ensure safety for all those aboard. Add the roomy cabin and high speed capabilities to the equation and you’ve got a boat that is great fun for everyone.

Models: F-22, 24, 25, 82, 27, 28, 31, 9A, 9AX, 9R, 32, 33, 33R, 33ST, 36, 39, 41, 44R

Length: 23’ – 39’4”

Cost: $$$ $$

Use: Sport cruisers/racers

One of the biggest names in the game, SeaCart is internationally noted for its high performance trimarans that far exceed expectations for a production boat of its size. The SeaCart trimaran performs as brilliantly off the water as it does on with its super-light and efficient harbor folding system, making light work of trailering. Notoriously easy to manage and maintain, the SeaCart 26 One Design is the ultimate day racing trimaran, designed for both course and inshore/coastal distance racing. Absolutely worth the international buzz it has garnered, the SeaCart is a thrill from beginning to end.

Models: SeaCart 26

Length: 26’

A high performance racer class, the Multi 23 is a lightweight, powerful trimaran known for its wicked speed of up to 25 knots. Multi trimarans of both available configurations were designed to give beach cat thrills and speed without any of the stability or seaworthy concerns. Open ocean sailing is no issue for the Multi’s big bows, which do their job to keep her stable. Built for sailors with a need for speed, the Multi makes a perfect weekend boat for racers, especially those with a taste for boat camping.

Models: Multi 23

Length: 23’

Another dual outrigger sailing kayak/canoe design, the Triak trimaran was designed to be effortless and fun, especially for beginners. Paddle the kayak with sails furled, use the foot pedals for an extra kick of momentum, or sail with just the mainsail – the only boat in its class to feature an asymmetrical spinnaker – for exhilarating speeds and a blast on the water. Car-top the Triak anywhere for a quick sail or plan for a week long expedition, but always count on having a great time on this easy little boat.

Models: Triak

Length: 18’

Use: Convertible kayak/trimaran

SeaRail trimarans are known for being affordable, light weight, trailerable trimarans that offer the perfect combination of exciting and relaxing experiences to a wide range of sailors. Whether it’s day sailing with your family, resort or camper sailing, SeaRail trimarans are ideal leisure vessels. Leave the hassle to the other boats – the SeaRail takes you from trailer to sailor in 15 minutes. But don’t let its reputation as a leisure tri fool you: if speed is what you want, rest assured that the SeaRail can deliver that as well.

Models: SeaRail 19

WARREN LIGHTCRAFT

Warren Lightcraft trimarans , another example of a convertible kayak-to-sailboat option, are known for their aesthetically pleasing designs that are also, as the name implies, very light for simple transportation and ease of use. Convert the kayak into a fast, high performance sailboat in just minutes, fly around on the waves all day long, then simply car-top the 68lb Warren for a maximum enjoyment, low-hassle day on the water. Perfect for sailors and paddlers of all skill levels, the Warren Lightcraft is the best of both worlds and an absolute joy to sail.

Models: Warren Lightcraft

Length: 15’6”

Built strictly with racing in mind, the Diam 24 is a light, powerful one-design class trimaran and a notoriously exceptional performer. Boasting blistering speeds of up to 30 knots, Diam trimarans are not intended for beginners. For racers who crave the very best in terms of intense speeds, smooth handling and impeccable performance, the Diam is the red-hot one-design racing tri for you.

Models: Diam 24

Length: 24’

For the sailor who prefers the finer things in life, the Radikal 26 delivers. Perfect for bringing the whole family out for a day on the water, this high performance, trailerable sailing trimaran strikes the most luxurious balance between quicksilver speeds and a smooth, comfortable ride. The Radikal 26 trimaran is as convenient to transport and set up as it is pleasant to sail, with a folding system that minimizes rigging hassle and also makes this a trailerable tri. Built for a fast and comfortable sail rather than a hold-onto-your-seats thrill, one-the-water safety and overall pleasure makes the Radikal 26 what it is.

Models: Radikal 26

Use: Sport cruiser

A solidly-built, single-handed trimaran, the Challenger also doubles as an adaptive design – meaning it is made to accommodate sailors of all levels of physical mobility. Best suited to lakes, the Challenger is a very safe, seaworthy boat for sailors of all ages and experience levels. Add to this the ease of owning, transporting and maintaining the Challenger trimaran and what you get is a simple, fun sailboat perfect both for beginners and those seeking a cheap thrill alike.

Models: Challenger

At a glance comparison:

Did we miss one? Let us know. Tell us what you sail and what you like about each boat in the comments below.

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2022 Sailing Special Buyer's Guide - from 20 to 30 feet

Article published on 26/11/2021

By Emmanuel van Deth

published in n°181 jan. / feb.

Most builders loyal to twin hulls have deserted the under 30-foot niche, and that’s a real shame. So in this bracket, it’s trimarans that are now more popular. Most of the models on offer are equipped with a folding or telescopic float system. These units can fit into a standard marina slip and can even be transported by road. And these features make them ideal for coastal sailing and for discovering waters far from your home port. Or why not a bit of racing?

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Astus 20.5 - Such success, now a one-design class Test MW171

This model has seen remarkable success, with 60 units already built since its launch in 2018. Our test revealed that this VPLP designed multihull is as fun to sail as it is practical and easy to operate. The most active owners have been working together with Astus Boats to establish a one-design class. The 20.5 is particularly exciting in the Sport version, as it offers 260 sq ft (24 m²) upwind for a weight of less than half a ton. Enough to have fun and sensation, especially when the gennaker is out! Like the other models in the range, it adopts a telescopic link system for the arms. The interior layout is compact, but still offers a mini saloon and a double berth. The strong points of the 20.5 for coastal cruising: pivoting appendages and a large 172 sq ft (16 m²) sailing platform.

Builder: Astus Boats Architect: VPLP Length: 19’6” (5.95 m) Beam: 8’2”/14’9” (2.48/4.50 m) Light displacement: 1,036 or 1,080 lbs (470 or 490 kg) Draft: 10”/4’1” (0.25/1.25 m) Upwind sail area: 226 / 260 sq ft (21 / 24 m²) Downwind sail area: 366 / 452 sq ft (34 / 42 m²) Gennaker: 215 / 280 sq ft (20 / 26 m²) CE category: C5/D7 Motor: 2 to 6 HP outboard Price: € 23,166 ex-tax (Leisure version)

www.astusboats.com

CORSAIR PULSE 600 - Radical and incredibly efficient Test MW148

As its name suggests, this sub-500-kilogram (1,000 lb) machine is designed for racing, and small fleets have appeared - notably in Australia. Though the Pulse 600 is the smallest of Corsair’s trimarans, it is still very attractive! Its three sharp and inverted bows give it a great look... a design as radical as it is efficient because on the water, you’re immediately won over by the potential of this machine. The cockpit is large enough to accommodate three people – and you can quickly hike out onto the floats to give the Pulse even more power. The removable coachroof houses a large watertight locker. No fitting-out or berths: it’s simply a shelter that can be used at anchor. The Pulse 600 is of course transportable and foldable.

Builder: Corsair Marine Length: 19’52’’ (5.95 m) Beam: 8’/14’9” (2.45/4.50 m) Displacement: 992 lbs (450 kg) Draft: 9”/4’ (0.22/1.20 m) Mainsail: 205 sq ft (19.10 m²) Jib: 76 sq ft (7.10 m²) Spinnaker: 345 sq ft (32 m²) Price: US$ 38,800 ex-tax

www.corsairmarine.com

TRICAT 20 - Perfect for rallies and performance Test MW163

This is the smallest model in the range: first presented three years ago, this trimaran was designed primarily for day-sailing, it also excels on coastal trips, where its compact size, maneuverability and performance are outstanding. The Tricat 20, with over 50 units already built, naturally reflects the success of its predecessors, including the 25 Evolution’s intelligent folding system, with the advantage of offering a nice living space and irreproachable seaworthiness for its size. Inside, there is a double berth for the parents and two bunks for the ...

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Lunada Design

Creative Boats for Home Builders

Category archives: demountable trimarans, back bay sit on top kayak, a modular system approach to sot kayak sailing, paddling and mirage drive propulsion.

Sit-On-Top (SOT) kayaks are easy boats on which to learn to paddle. They have none of the “get in the coffin and you are about to drown” psychological identity that one finds in the Sit-Inside boats and they’re amazingly adaptable to a wide range of paddling activities. It also doesn’t hurt that they are pretty straightforward boats to rotomold, which makes them very cheap to produce in large numbers.

I didn’t envision just one boat for this niche in the home-built kayak market. Instead, it came to me that there would need to be at least three models that could address the wide-ranging styles of boating interests in this area of the kayak world. The result was a couple of very clean, SOT models at 14’ and 16’ called the Corona and the Back Bay, respectively. The third model was going to be called the Wahoo, as it was specifically designed for the folks who spend a lot of time fishing with their SOT’s. I’ll get to the Wahoo in the next article.

As a canoe and kayak sailor and a guy who had just been out for a test drive on the Hobie Adventure Island, which is based on their 16’ SOT Adventure model, I wanted to offer my own take on what makes for a truly fun and stylish, sailing SOT kayak. The result was that a fully integrated system of component parts was designed for the basic Back Bay. This modular approach allows the Back Bay to go sailing by simply adding a system of light-weight, easily built elements that quickly convert the SOT to a single aka sailing boat called the Scorpion, OR, to a double aka sailing boat with slightly larger ama volume, called the Doubloon. Of the two configurations, the Doubloon is most like the well-known and highly respected, Hobie Adventure Island.

The Corona and the Back Bay are virtually identical models, save for their respective lengths. For the purposes of this article, I’ll focus on the Back Bay version and all the potential add-on systems I’ve incorporated in the design.

THE BACK BAY SOT KAYAK

Specifications: Length overall – 16′ Beam overall main hull – 28″ Depth of hull max – 12” Weight – 48 lbs. or less Displacement – 335 lbs.

This boat is built in the S&G style of construction in 4mm marine ply with 6 oz. plain weave fiberglass set in epoxy on the inside and outside of the hull for full laminate sandwich strength. The build process uses external cradles as building supports, ensuring that the hull goes together with minimum hassle when handling the rather slender and longish hull panels. The boat is bulkheaded internally at three key points. These bulkheads create not only integrated strength in the design, but they also cleanly separate the hull cavity into four unique volumes for gear storage and watertight flotation.

The Back Bay can be configured with a large, open tankwell set aft of the cockpit, or built with a watertight, aft hatch cover for internal storage in a conventional kayak style.

Specifications: Beam overall – 10′ Weight (est.) – 90 lbs. Sail Area – 56 sq. ft. Displacement – 350 lbs. Draft (board down) – 28″

The Scorpion variant is a Sit-On-Top design for fun sailing, paddling, or Mirage peddling… or all three, as the builder desires. There will be a design for a leeboard mount included in the plans for those who are going to build the boat for sailing. Having the aka gull wing form set well forward permits a full paddle swing arc. The aka beam connectives to the amas is split into a pair of mounting elements. I did this to make for a stronger, single beam mounting struture. With a single beam design, there is a tendency for the am to want to rotate around the beam, making for a very stressed component that could lead to early failure. By splitting the beam and spreading the mounting points, I have given the structure more resistance to this rotational force, making for a more rigid boat in use. This setup will allow the owner to power sail in light air with both the paddle and the sail providing thrust. With the leeboard swung down for sailing, the owner can do some “power sailing” and utilize the Mirage drive, as well as the sail, in light conditions. The Mirage is capable of boosting boat speed enough that it creates apparent wind over the sail, adding power where there really isn’t enough for sailing alone.

The amas are positioned to optimize capsize resistance when sailing off the wind. The amas do not touch the surface of the water at rest in stable trim and provide only minimal wetted surface drag when underway by paddle or peddle. As soon as the sail is loaded by the breeze, though, the ama on the lee side begins to immerse, firming-up the boat and resisting the heeling moments being generated.

The aft deck can be configured as a watertight hatch with full access to the aft sections of the hull, OR a large, diving tank well with self-draining ports. The cockpit is fitted with self-drain ports under the seat as well as forward, in addition to the daggerboard slot. There is a watertight deck plate just forward of the seat, between the knees of the sailor/paddler to provide secure storage for critical items that may be needed on a routine basis. The foredeck has a watertight hatch cover for bow storage needs.

The rig is a fully battened Dacron sail with two reef points and a multi-section, self-supporting mast which steps into a sealed mast socket in the hull. The mast and boom sections can be aluminum or carbon, as budget permits. The sail choice is open for the customer as long as it can be balanced with the fixed positions for the mast and dagger board. The Cunningham is run to the deck of the gull wing aka to keep the rig on the boat in the event of a capsize.

With 56-sq. ft. of sail on a 90-pound boat, this will be a decently speedy boat without being in over its head all the time in a stiff breeze. I suggest two reef points in the sail to allow for sailing in a wide variety of conditions.

This will be a wet boat at speed, yet there are no worries at all for flooding and sinking, save for a truly nasty trip over a reef that shreds the entire underside of the craft. The bow, cockpit and aft hull volumes are all independent, sealed compartments, as are the ama volumes.

Reentry from a swimming session will be easy with a simple, sling, or rope ladder much like those used by rock climbers, called etriers.

The boat is constructed in a multichine, marine plywood style with epoxy glass laminates inside and out in a stitch and glue style. Stainless T-Nuts are embedded in the hull deck surface from below to provide a secure set of mounting points for the aka wing. The amas are held in place on the aka tips by large bungees and a notched lock system. This system provides for quick setups on the beach.

You just fit the aka to the foredeck, insert four, 1/4″ threaded stainless screws with comfortable, knobbed grips and screw down the aka wing. The amas slip onto the ends of the aka and you lift the pair of 3/8″ bungees up and over two raised hooks on the aka ends to secure the ama in place. Simple, easily maintained and near foolproof in operation.

DOUBLOON SAILING SOT

The Doubloon is the second variation on the central SOT theme of this group of boats. In this design, I am looking to provide a more expansive utility application for the base, Back Bay SOT version. The Doubloon is essentially a solo craft and it carries the same, 56 sq. ft. sail, but the overall potential of the boat is expanded through the use of dual akas and full trampolines on both sides of the Back Bay hull. The rendering of the Doubloon shows a daggerboard inserted down through the Mirage Drive trunk, but in use, I would prefer to have the board mounted outside the Back Bay hull as a leeboard. Plans will be supplied with the leeboard solution.

The akas on the Doubloon are spaced to allow for a full paddle stroke with the boat setup as a trimaran. There are two sections of tubing that span the opening fore and aft between the akas from which the tramp is mounted. The trampolines are designed to roll-up on the outer tube section, much like a window shade and they are deployed by an endless loop of light halyard line. With the tramps fully deployed, the inner tube section lifts up and over a holding pin in the aka and the sailor applies as much tension to the tramp as he feels he needs by hauling-in the endless loop line and cleating it off. If a paddling session is desired, he simply pops the jam cleat and pulls the line to roll-up the tramp on the outer tube section. This procedure applies for both port and starboard tramps.

Like the Scorpion, the Doubloon can be built to utilize a Mirage drive in the center well and the need to roll-up the tramps for paddling is essentially negated, (though it is nice to have the option once in awhile as Mirage drives can be difficult to maneuver in tight places)

The aka beams are held to the deck of the Back Bay hull with the same, threaded knob strategy for quick setup and takedown times. Similarly, the amas are held to the aka ends with hefty bungee cords for the simplicity of use. There’s another, rather invisible, benefit to using the bungee cords for ama mounting. Because they are being held in place through a fairly dynamic hold-down system, the amas can move about, ever so slightly, while underway. This allows the amas to have some structural “give” and the result is that the banging and thrashing that is typically experienced by the ama, is somewhat dissipated through the flex of the joining system.

All in all, I think the Back Bay SOT should be a really fun boat to own for warm water/warm weather boating adventures. It has the capacity to carry enough gear for several days out on the water. When rigged with a sailing system of your choice, it can also cover some pretty good distances if the winds are favorable. Plans for this boat and all its variations will be available from this site and Duckworks Magazine.

Chris Ostlind

Lunada Design Chris@Wedgesail.com

Solo 12 and 14, corsica 15r, sports car performance on the water.

Over the past couple of years, I have taken a break from my boat design work. During that time, I’ve been able to reassess my connection to the craft. The last boat I designed was the Europa 20, which is a trimaran meant for vertical strip foam construction with sandwich style, infused epoxy/glass laminates inside and out. The Europa is a boat for very fast day sailing with a very light hull and a very big rig. A boat that is not for everyone, to be sure, as it requires a level of skill that the average guy does not typically cultivate in the course of experiencing their recreational boating interests.

In stepping away from the larger, more powerful beach type multihulls, I came around to the desire to produce a smaller, very quick and sensitive boat that would appeal to recreational sailors and not just those guys who want to blast around with their hair on fire (though I do suspect that in the right hands, this boat will do just that). The new design had to be easy to build with standard, marine plywood/epoxy/glass techniques that did not rely on exotic layups with spendy carbon cloth. (Well, maybe the carbon will sneak in there a bit on the beams for the guys who want to play with a bigger rig)

Looking long and hard at the smaller skiff-like hull designs I had done before, such as the Montage, I decided to draw the new boat in that same general size, but with a very different approach when it comes to how the boat achieves its performance potential. Where the Montage has a relatively spacious cockpit capable of taking on a couple of adults, (or a parent and a couple of smaller kids) the new, Corsica 15R trimaran would be for one adult (or accomplished kid) designed solely for a unique, one-up sailing experience within the small beach multihull genre.

As a result, the boat has minimized clutter when it comes to excessive high-tech trickery. With that approach, the Corsica 15R is also going to be a boat that has much lower maintenance requirements in order to keep it in top sailing condition, as well as a much lower realized cost to get it on the water and ready to sail.

If you are into cars, as I am, then think in terms of a nicely pumped, Mazda Miata, type of boat that would be a cool, weekend canyon racer for one person. A boat that could blast around the local waters in a good breeze and give chase to other small, fast, multihulls being sailed by crews of two.

The result of this conceptualizing process is the Corsica 15R. The C15R is a boat of modest, marine plywood build techniques and is very light weight for its generous sail area. With this boat, the normal sailing position would be the skipper, semi-reclined within the main hull, driving his machine like an F1 Grand Prix car. In this configuration, the boat is designed to utilize foot pedals for steering, leaving the hands free to work the sheets. But, that’s not the only way to sail this boat. Owners who wish to sail in a more conventional multihull style, can sit-up out of the cockpit and onto the main hull cockpit gunnel, or even the trampoline surfaces all the way out to the ama, where they will steer with a tiller extension.

A construction style in multichine, 4 mm marine plywood, allows the boat to be assembled in a well-understood fashion that will go together quickly. With a subtle placement of minimal stringers and sufficient bulkheads, the C15R becomes a strong main hull shell that can absorb the loads from its sizeable rig, turning the power of the sails into forward thrust in the water.

There is no fully enclosed transom on the vaka hull. The cockpit deck is slanted gently down and aft for automatic self-draining, such as is seen in sport dinghies and larger race boats. A collection of bulkheads under the cockpit deck provide structural support and watertight compartments ensuring that the boat will not likely sink even if large sections of the bottom are torn out from an underwater hazard while smoking along in a gin clear lagoon.

The demounted boat can be assembled easily by one person. The gently gull-winged akas are built with a glassed box beam core. The inboard ends of the akas slide into tapered sockets in the main hull and are levered in place with stainless waterstays to make ready for sailing. This, tapered socket technique prevents binding while assembling the boat, while providing a solid, hassle-free and weight minimized demounting system. The leading edges of the akas are smoothly shaped foam blocks that are glassed onto the box beam to provide an aero component, as well as creating reduced drag from waves and spray. The akas are hard fastened to the amas as a complete assembly that is easily removable from the vaka hull. The trampolines stay mounted to the akas and amas for transport and only have to be hooked and tensioned to the main hull during assembly.

The mast is a stick from a Hobie 16. I specify the addition of a set of spreaders from the Hobie 18 mast to stiffen up the H16 mast to handle the additional righting moment generated by the Corsica design. Naturally, I’d prefer to see fresh sails in something like fully battened, Pentex laminate, but builders on a tight budget could also work with a loft service to tweak a reasonably fresh Hobie 16 main and jib and do just fine. The addition of reefing points on the main are strongly suggested, as well as the use of furlers for the jib and spinnaker/screacher. For those who desire fresh sails for this boat, I would recommend the folks at Whirlwind sails in San Diego, California. http://www.whirlwindsails.com/

A removable carbon prodder sets the tone at the front end of the boat. The stick originates as a carbon windsurf mast, so it is easily found on the used market and equally replaceable, should it get poked into an unyielding environment. For trailering, the sprit unpins, slides out of its socket and is stowed in the cockpit for transport and storage.

Corsica 15R Specifcations

LOA 14’ 11” (4.54 m)

BOA 13’ (3.96 m)

Displacement 650 lbs. (294.8 kg.)

Sail Area (upwind) 218 sq. ft. (16.17 sq. m)

Spin 142 sq. ft. (13.19 sq. m)

Mast Length 26’ (7.62 m)

Draft (board up) 1’ (.3 m)

Draft (board down) 42” (1.07 m)

The mast is raised by the traditional beach cat method of physically lifting the mast with the base pinned to the mast step, or by utilizing the long daggerboard in its trunk as a form of a gin pole. A forward hoisting line is led over a pair of sheaves at the top of the daggerboard and down to the hand cranked winch on the trailer. Mechanical leverage quickly raises the mast so that the forestay can be fastened to the bow, stepping the mast securely. You can see a few photos of the process at Brent’s L7 trimaran site:

http://home.comcast.net/~ritakend/site/?/page/Mast_Raising/&PHPSESSID=864f3404e3f46ed29dd99b863018fc1d This is a very simple way to raise a mast should you need to avoid the trad lifting exercise for one reason or another.

I chose to not go with tricked-out, curved lifting foils in the amas due to construction complexity and added cost for the builder. Foils of this type are hard to build correctly by hand, as are the needed curved trunks in which they slide. Instead, the boat is equipped with a daggerboard that is inserted through the deck of the main hull in front of the mast which angles aft to exit the hull below the waterline. A daggerboard and trunk of this type are much simpler forms to build and orient in the hull. It is also just one main foil, where lifting foils need to be made in pairs, one for each ama. Lifting foils also need complex control mechanisms to retract and deploy the foils and they have to work from the cockpit remotely with the foils mounted way out in the amas. The needed controls are an interesting problem when the boat is 13’ in width and the driver is semi-reclined in the main hull.

Note: I’m not against an owner who might want to experiment with foiling for this boat, even if it is just foil assist and not full flying. It would require a lifting t-foil style rudder and twin Bruce style foils in the amas, or, if a person is really accomplished as a composites builder, they could make a pair of matching c-foils for the ama. The owner just needs to know what level of additional work is involved and at what skill level they need to perform in order to get the desired result.

If you are on a budget, the rudder and headstock from a Hobie 16 will work just fine for the Corsica with some mods to the tiller. The more deluxe, Rudder 25 system from Dotan will also work well, should you have the coin. http://www.dotan.com/ If you plan on pushing the boat hard, then a longer blade will be required, or you can get yourself invested in the process of putting a rudder on each ama and have stunning control at your finger tips. On the down side, that change will cost you a bit out of your pocket and at the launch ramp in setup time… though I can see a nifty rig with light alu tubing and the use of snap buttons as a cool solution.

The Corsica 15R will be a light boat built from familiar materials. It should be a fairly simple building experience for the owner and will fit comfortably into any typical garage space, making it easy to find a building location. It will quickly assemble for sailing and be hassle free with minimal maintenance required to keep it in top form. It can be towed behind any compact car on a typical beach cat trailer and when demounted for travel, is road legal anywhere in the world. On the water, this boat should be quite quick and behave with predictable, pin-point sailing manners. With the skipper slung comfortably in his reclined cockpit seat, he will be decently protected from the effects of the weather and sea state while tearing around his local waters.

NAGARE 21′ AND 17′ MIRAGE DRIVE SPEEDSTERS

Making use of mirage drive propulsion with more efficient hulls designs.

Nagare (nah-ga-ray) is a Japanese word meaning Flow.

Both of them are configured as trimarans with fairly small and unobtrusive amas designed to give the boats remarkable stability in a wide range of conditions while allowing the vaka, (main) hull to be decidely slender for more effective drive through the water.

The Nagare sisters also have incredibly narrow waterline beam numbers that, when coupled with their fairly long hulls provide for very easily driven hull forms for high efficiency per unit of energy applied.

I expect both boats to operate at the very high end of commercially available paddled boats of the same length, beam and weight. So, yes, they can go pretty quickly, but that’s not the real purpose.

The real benefit of the design genre is through the ease with which they are propelled at any given speed, compared to other boats of their size. This efficiency translates directly to those using the boats as less tiring for miles covered, or greater speed with the same effort as other, wider designs.

Because the propulsion is derived from the largest muscles in your body, the leg muscles, rather than the arms and shoulders, there will be less fatigue for each mile traveled. Because leg muscles are so much bigger than arms, they will be able to do more work in a given period of time, making for longer possible trips, as well as the mentioned lower fatigue issue. With a less fatiguing effort, more people will be able to enjoy the experience of being out on the water for daylong adventures.

NAGARE 21 DOUBLE SPEED AND STABILITY FOR DOUBLE RECREATIONAL BOATERS

The Nagare 21 uses a set of amas, mounted on a pair of simple, anodized aluminum tubes with quick release snap buttons holding the sections together for easy disassembly for car-topping. If a trailer is used to transport the boat, the beam of the Nagare 21 falls well below trailer maximums, so nothing special needs to be done to take the boat to and from the water. Two Nagare 21’s can be trailered, or car-topped, by removing one of the amas and placing the main hulls close to one another on the racks, or trailer. The removed amas easily fit inside the hulls and they are ready to go. The whole affair on the rooftop is very much like a pair of sea kayak doubles. Because of the length, I would not mount a boat this big on any compact cars. You would be very likely to rip the rack right off the roof in strong side winds.

Steering is by means of a simple, flip-up style kayak rudder with control lines run through the hull to a convenient steering lever in the cockpit. I suggest the SeaLine SmartTrak rudder system (do a search for supplier), the P-41 Multi-purpose rudder from Onno Paddles http://www.onnopaddles.com/onnocomponents.html and the Feathercraft rudder system for hardshell boats. http://www.feathercraft.com/accessories/rudders-hardshell.php These are really great rudder units and will give excellent steering control with minimum drag.

NAGARE 21 SOT OPTION

This boat can be built with a full cockpit tub so that it functions as a Sit-On-Top kayak with full drainage through the Mirage drive openings. Auxiliary drain ports are located in the tub for rapid removal of any water that comes in over the side of the hull. I suggest the SOT option for warm water users, with the more traditional kayak style, Sit-Inside hull form for those who will be using the boat in colder water, or more frequent inclement weather.

The SOT version has internal bulkheads for support of the SOT tub, along with the capability of adding a small circular deck plate for an additional watertight compartment in the cockpit that is perfect for small items, such as cameras, wallets, car keys, etc.

The SOT variation is an optional element to the base plans. If you wish to built it as an SOT, drop me an email at my regular email address and I’ll get back to you.

ROUGH WATER USE

This is not really a boat that is meant to go out in rougher conditions, such as those where a full-blown sea kayak might be right at home. It’s meant for quieter waters, such as lakes, bays, harbors and bigger rivers. It can take a session in 1 or 2 foot breaking surf, but I would not expose the boat to bigger waves, especially in a shore break scenario. You may find yourself out from the shore a bit when the wind comes up, producing steep, choppy waves. The basic Nagare 21 will handle this easily because only the cockpit will be exposed to swamping. The amas will keep the boat stable while you pedal to shore, or a quieter place on the water, where you can bail-out the boat and continue.

It is a perfect boat for sightseeing, bird watching, fishing, photography, and just simple, energy efficient cruising with near bomb-proof stability (you can stand up in the boat while out on the water without your partner coming completely unglued, for instance).

The Nagare 21 is a fast, comfortable and unique boat for a couple who like to get out on the water, but do not want to hassle with the business of capsize that is present in other types of boats, such as kayaks and even canoes.

NAGARE 17 SINGLE A NEW STYLE OF SOLO BOAT FOR TROLLING FISHERMEN

The solo version of the Nagare series has some very different twists, compared to its bigger sister. It has the same, highly efficient and easily driven, slender hull technology, the same set of trimaran style amas well aft for big time stability, the same generous cockpit opening and the same convenient utility for car-topping or lightweight trailering.

The design elements that set this particular boat apart from its sister craft is that the Nagare 17 has a very special capability when it comes to fishing.

AFT FACING TROLLING

Anybody who builds the Nagare 17 and intends to use it for fishing will probably be knocked-out by the potential for facing aft while trolling. Imagine using your legs to quietly drive the boat forward while you casually set trolling rigs, eat a sandwich and keep an eye on the fish finder… all while keeping an eye on the rigs you have set, with them easily at hand?

This is the signature utility development with the Nagare 17, designed specifically, for fishermen. It works like this…

The fisherman loads his boat, drops into the forward facing seat, hits the iPod for his favorite tunes and jams out across the lake at a remarkable speed for a human powered boat. He zips across the lake in virtual silence because he’s driving a very skinny and efficient hull with no engine sounds. Once he arrives, he’s going to make a few sneaky trolling passes with his Mirage drive pushing him along over that monster crew of Pike that are hanging around on their favorite piece of structure. Wham! Fish On! and the day starts with smile on his face.

If you’ve ever fished from a typical Sit-On-Top, you know that you have to face forward while trying to look over your shoulder while trolling. Hook-up and then you have to swivel around, grab the rod and go after the fish. All the time you are doing this, you have to balance the boat carefully, because the whole tamale could go over and end your day right then and there.

Well, that’s how you used to do it, anyway.

With the Nagare 17, you can take it to a whole new level of fishing pleasure. The Nagare 17 is equipped with twin Mirage drive trunks. When driving the boat forward and facing forward, the Mirage drive is dropped into the forward trunk and a tractor-style seat is dropped into the aft trunk with the seat bottom resting on the top of the trunk.

To convert the boat to aft facing trolling and fishing, you simply stand up in the boat and swap the Mirage drive for the aft mounted seat plug and the seat then goes to the front trunk… facing aft. With the Mirage drive still set to drive the boat forward, you simply sit down and start pedaling, slowly, up to your desired trolling speed.

Now, you can watch your fish finder, GPS and your trolling rigs while you continue to tool along at your favorite speed for nabbing the fish. Get one on and simply work that rod while continuing to face aft. No twisting around in your seat, no ”just about dumped it” scenarios, just simple, fun fishing in a very stable boat. What could be cooler than that?

With the fore/aft balance point of the boat set right between the two drive trunks, there is but a very minimal change to boat pitch when you change the direction you face.

The Nagare 17 is further designed to accept an insulated and watertight tank between the two aka tubes where they run through the aft deck. You can use this for all kinds of stuff like: your catch, fresh bait storage, cold beverages if you catch and release… whatever suits your needs. There is plenty of room between the two drive trunks for a pretty good sized tackle box and lots of room up forward of the trunks for any of that “other stuff” that fishermen seem to sneak aboard their boats.

A moveable electronics unit can be fastened at the forward end of the cockpit, or unhooked and moved around aft if you’d rather have it facing that way.

Maybe you want to cast lures or flies instead of troll. The boat is so stable with the two, wide set amas, that you can stand up and cast all day without ever feeling like you are getting the least bit tippy. All in all, the Nagare 17 is quite a boat for fishing, as well as just plain fun, recreational pursuits.

The Nagare sisters represent a unique design family for human powered vessels. They are quick, stable and with their unique styling, represent a distinct departure from the looks of traditional boats one typically sees on any given shore or launch ramp. Both boats are designed to be built in marine ply Stitch and Glue methods for the hull sections, with cedar stripped decks to take advantage of the really beautiful, smooth curves capable from that style of building. You can paint the lower sections of the hull and leave the cedar decks natural with a deep varnished finshed, for a real knock-out boat that will really gather a crowd.If you really want to have a plywood deck build instead of the cedar strip build, write and twist my arm gently. I can design that change for those who really like to build that way

Plans are not yet complete, so if you would like to build one of these two boats, please send me an email and I’ll put your name on the mailing list for information, or watch the plans section of Duckworks for the notice.

CHRIS OSTLIND LUNADA DESIGN CHRIS@WEDGESAIL.COM

Another Trimaran/Skiff … Bigger, With More Power

Well, you had to know this would happen…

When the Montage Skiff/Trimaran was introduced, the Lunada Design website was absolutely flooded with an ocean of page hits every day right after the article was posted. I received several dozen personal query letters regarding the boat and sizeable slice of them were directed at the potential of a bigger version of the Montage.

The concept of being able to build your own boat and rig it with a used mast and possibly even used sails, (if they are in good enough condition) had struck a chord with the homebuilding community. The creation of a larger version of the Montage would take the specified rig choices up into the much more commonly found beach cat rig sizes and make the business of finding a used rig in great shape, a whole lot easier. After pencilling a collection of thoughts and running some rough numbers on the potential, the idea came into focus as the 18′ Collage.

The ama shapes, especially on the smooth hulled variation, borrow other design cues from the modern performance dedicated French designs of VPLP, as well as the very cool work of Nigel Irens. The transoms are nudged in the direction of a triangular shape, while retaining some of the typical beach cat, flat-topped U-form feeling. The volume concentration is well-forward, with the foredecks being much more rounded to provide rapid shedding of water. These shapes will help to reduce the tendency of multihulls to pitchpole when sailed hard.

Breaking away to some degree, from the single, build style of the Montage offering, the Collage is presented as a fully strip built, smooth hulled version, as well as a multichine plywood version. These choices will give builders the ability to work with the material choices and aesthetics they prefer. I am also looking at the potential for a foam cored sandwich laminate boat using the vertical strip technique, though that iteration will probably come around a little later in the process.

Collage Specs

LOA 18′ ( 5.48 m ) BOA 14′ ( 4.26 m ) BOA main hull 41″ ( 1.04 m )

Sail Area Main 163 sq. ft. (15.14 sq, m.) Jib 55 sq. ft. ( 5.12 sq. m. ) Spinnaker 161.5 sq. ft. ( 15 sq. m. )

Displacement 1000 lbs. ( 454.5 kg. ) Weight 380 lbs. ( 172.7 kg. )

The Collage meets all the same design criteria as does the Montage, except it’s longer and wider, has more sail area, carries more crew weight and yes, it’s going to be faster in the right hands. Faster… sometimes this term can be kinda self-defeating when speed claims are made compared to another boat. When it comes to recreational boats, I’m of the opinion that speed is a relative thing based on the overall design brief of the boat in question. In the case of the Montage and Collage designs, speed is one of the attractive elements as long as it is kept in perspective with just what the use application will be from day to day. From where I sit, this will be primarily recreational purposes.

The Sail Area to Displacement ratio ( SA/D ) for each of the boats is as follows: The Montage is 31.56 and the Collage is 34.88 With both of these boats being sailed at near max displacement, I give the nod to the Collage, based on waterline length, as well as the ability to punch through wave conditions that will toss the Montage around to some degree.

I would like to see this pair of boats ( Montage and Collage ) blasting around in the hands of skilled sailors. There’s nothing quite like the feel of a performance boat and the way it can deliver the exhilaration of a spirited ride. But… I’d also like to see this boat out on the water being used by families while they have a really fun day on the water with, maybe, a somewhat toned-down speed blast tossed into the mix every now and then to get the kids chirping.

I’m looking at the potential for the Collage to create a new beach and/or lake sailing culture in which energetic hot shoe dudes, as well as young sporting families, can all mingle on the beach, out on the water and share a communal BBQ after the day of sailing. I grew to maturity on the beaches of SoCal watching the brand new Hobie Fleets do this very thing and it was a lifestyle that perfectly fit my beach kid way of thinking. It would be great to see that happen once again. Could this take place in 2009? Hey, I don’t know the answer to that one, but it is fun to think of the boat and its owners in those terms.

There’s a lot going for the Montage/Collage design approach to support such a social event concept. Both boats are affordable to build, they are easily trailered by even sub-compact cars, they make use of “experienced” parts that can be had on the open market for pennies on the dollar when compared to new parts and they are boats that are easily sailed on the first day. This last part is important, as the boat will attract more enthusiasts when they see that they can be sailed with what pretty much passes for beginner’s skills. Just because it can go fast, does not mean it has to be sailed that way. As the owner’s skills grow, the boat’s potential will be there waiting for him.

As a way of introducing the Montage and the Collage designs to the homebuilder market, I’d like to offer free plans to one person. This builder should be able to show me that they have a very strong interest in either design and are willing to build the boat as I supply the plans in accordance with their progress from the previous plan set delivery.

If interested in this offer, you can write me at: Chris@Wedgesail.com or at lunadadesign@gmail.com and make your pitch. The one chosen to receive the free plans will be willing to provide construction photos of their progress and a brief written description as to how things are going. The personal accounts will be published on this website, Lunadadesign.net so that the readers of the site can follow the projects.

Chris Ostlind Lunada Design

This boat created immediate appeal to beginning and intermediate sailors. It offers much of the speed experience of a high performance skiff in a stable and predictable platform that is really tough to capsize. The Weta is one of the first boats to encourage family participation and reintroduces the waterborne fun of the beach sailing culture, established way back in the late 60’s with the intro of the Hobie catamaran.

A brand new, factory built Weta goes out the door for USD $11K. Realistically speaking, this isn’t an in surmountable amount of money for a factory produced, brand new carbon trimaran. It is, however, quite a lot of money for most casual recreational enthusiasts and the folks who like to build their own boats… especially when you consider the rugged economic conditions we all face these days.

The estimated $5600 figure represents a boat with a whole host of brand new parts. For the clever builders out there, the Montage could be even less expensive if they can find a used 470 rig, perhaps a used small craft, or beach cat trailer that could be modified to fit the hull design and even a collection of hardware in good condition. The Montage is a very light boat at right around 235 lbs., so you do not need to buy a heavy duty trailer.

I went back to the drawing table and reconfigured everything so that the longest hull panel was going to just fit on a couple of sheets of marine ply laid end to end. The main hull also got just a bit wider in the process of lengthening the boat. Where the factory boat uses carbon fiber on foam cores for its structure, the Montage will be a 4mm marine plywood design with full fiberglass/epoxy sandwich laminates inside and out. The foredeck and the cockpit seating transitions are strip-built in Red Cedar to give the overall appearance of the boat a smoother, more organic feel than straight plywood panels.

The amas for Montage came from a 16′ trimaran design that I had already done and required minimal re-design to work with this boat. The amas are also designed as multichine ply forms with pretty high volume shapes well forward and a water shedding deck form that will helps to keep them riding high even when driven hard. Ama displacement is 100% of the all-up boat weight when sailing.

Montage Specifications

LOA 15′ 6″ BOA 12′ BOA main hull 41″

Main 110 sq. ft. Jib 38 sq. ft. Screacher 102 sq. ft.

Displacement 650 lbs. Weight 235 lbs.

The aka beams are anodized aluminum instead of carbon tubing. The inboard ends fit into fairly burly sockets in the hull and are held in place with quick release pins. Flat deck flanges on the ama ends are welded in place and bolted to the amas. The amas are removable from the aka tubes for repair or maintenance, but otherwise stay mounted, along with the trampolines, as complete units.

The mast is also anodized aluminum. The boat uses the same mast section as the 470 dinghy, which is a Proctor Cumulus section. This mast is available on the used market with a little bit of hunting around. If you want it all and have the money, then there’s a very cool, filament wound Forte carbon spar available with very close specs to the Proctor that will rock your world. http://fortecarbon.com/

Making these two changes from the benchmark, all-carbon Weta to an aluminum spar and tubing keep the costs down, with but a slight weight penalty over all-carbon parts. If you find a used mast, the savings will be even more substantial.

I have found that the more expensive sailcloth laminates are capable of driving the boat just a bit faster, but for the average recreational sailor, they will hardly ever make a difference compared to more forgiving sails in Dacron. Dacron is much easier to maintain, lasts longer, is a lot more tolerant of UV exposure and can be repaired by any sail loft wherever you go. If the builder of the Montage really wanted to, they could buy a set of sails in something like Pentex laminate instead and they’d have that hot, performance boat look that some desire along with just a bit more zip under sail.

The aluminum aka tubes will be sold pre-bent and ready to install on the amas. If the builder has access to a good mandrel bending facility that can handle the OD/ID specifications of the tubing, they can fabricate their own tubes to supplied specs.

The Montage is designed to be a really fun day sailing machine that can generate near performance skiff sailing speeds while offering a hugely stable platform for recreational sailing. Construction of the boat is very straightforward in marine plywood with glass/epoxy laminates and can be easily built by any sailing enthusiast who has household handyman skills with tools. The Montage has been created to offer homebuilders an opportunity to enjoy this style of family sport boat at a completed cost that is far less expensive than the manufactured version.

CHRIS OSTLIND

Fresh take on the solo16 s, a safe, speedy solo cruising craft for adventurous souls.

After a lot of input from readers of this site, I have completed the modifications to the Solo16 S design that reflect many of their expressed interests.

The Solo16 S now has a bit more displacement as a direct response to suggestions for the use of a small 2 hp outboard and some spare fuel. At the same time, the vaka hull was given additional beam above the waterline and the shear was raised some to allow for mods to the amas.

The amas, themselves, were made slimmer and taller, while retaining the same volume. They now have a slight vee section which gives the boat a progressive resistance increase as the amas are pressed heavily in a gust.

To complete the changes, a sporty all-weather soft cabin has been designed to allow the owner a chance to sail in a wide spectrum of conditions. The new cabin is modular in its approach with the ability to address a multitude of sailing situations.

All panels except the Bimini have generous window areas which are backed by micro mesh screen that is small enough to keep out the No-See-Ums. The PVC windows are zip-out removable and the screens can be rolled-up for maximum airflow through the cockpit. The complete enclosure system allows the owner to mix and match the panels as needed for the best protection from the elements.

When setting up the boat for sailing while on the trailer, the owner simply lifts the ama assembly, rotates and places the ends of the aka tubes into the matching vaka openings and slides the ama into place. The akas are fully seated when their internal, spring loaded snap-buttons click into place. The entire ama assembly is easily handled by one adult with modest physical strength.

In the trailering mode, the complete boat does not exceed 68″ (1.7 m) in width, falling well under every trailer width limit in the world.

Trimaran - Multihull Component Terms

Multihull Component Terms

There are three terms that describe the components of modern multihulls. The term vaka , like the related terms aka and ama, come from the Malay and Micronesian language group terms for parts of the outrigger canoe, and vaka can be roughly translated as canoe or main hull.

Vaka - A proa consists of a vaka, the main canoe-like hull; an ama, the outrigger; and akas, the poles connecting the ama to the vaka.
Aka - The aka of a multihull sailboat is a member of the framework that connects the hull to the ama(s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans.
Ama - The term ama comes from the proa. The vaka is the main hull, the ama is the outrigger, and the aka or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimarans.

Semantically, the catamaran is a pair of Vaka held together by Aka , whereas the trimaran is a central Vaka , with Ama on each side, attached by Aka .

The above section reflects American usage. In the UK the main hull of a trimaran is called simply the main hull or centre hull . The side hulls are floats . The structures between the main hull and the floats are called the wings and the structural portions thereof are beams . In cruising trimarans the wings are solid and cabin accommodation extends over them, while in racing trimarans accommodation is limited to the main hull and the wings are open sheets of netting.

Famous quotes containing the words component and/or terms :

“ ... no one knows anything about a strike until he has seen it break down into its component parts of human beings. ” — Mary Heaton Vorse (1874–1966)

“ The Catholic Church has never really come to terms with women. What I object to is being treated either as Madonnas or Mary Magdalenes. ” — Shirley Williams (b. 1930)

Boat Profile

Seaclipper 16

A folding trimaran for the home builder

From Issue January 2017

I ’ve built more than a few boats for myself in the past 38 years, and in all that time I have never been tempted to build a multihull. Why go to all the work of building two hulls, let alone three, when I’ve never found any of my single-hulled boats lacking in any significant way? I started getting answers to that question as soon as I stepped aboard a Seaclipper 16 designed by John Marples of Searunner Multihulls and one of nine designs in the Seaclipper series of trimarans. The hull is constructed of 7 sheets of 1/4″ six-ply marine plywood, five sheets of 3/8″ nine-ply, and lumber in commonly available sizes. Fiberglass-and-epoxy sheathing is optional. The instructions are geared for novice builders; full-sized templates for the bulkheads are provided in the plans. Stringers connecting the bulkheads define the shapes of the plywood panels for the hulls. The 15′ 11″ vaka (center hull) has a flat bottom that will take to landing on the beach without digging in or causing the kind of wear you’d get with a sharp V hull. The amas (outrigger hulls) have bottom panels set at an angle, deeper outboard than inboard. This configuration adds a fin-like element for increased lateral resistance for sailing in shallow water with the daggerboard pulled up. The angled ama bottoms also present an edge to the water, keeping the amas from slapping the waves when they’re close to the water’s surface; it’s a quieter ride. The amas’ bottoms are positioned higher than the vaka’s bottom, so their edges are not subjected to wear when the boat is hauled up on a beach.

Each of the four swing-arm akas has three bolts: one securing the pivoting part of the aka to the ama, and two (one of those anchoring the shroud bridle) connecting the pivoting part of the aka to the fixed central section on the vaka. Removing the inboard bolt allows the swing arm to pivot, moving the ama aft and inward.

The akas (crossbeams) can be made in three ways: as one piece bolted to the three hulls, hinged to fold the amas on top of the vaka, or as swing-wings, like LIMONADA shown here. With the swing-wing, the amas pivot aft and nest against the vaka, bringing the beam down from 11′ 3″ to 7′ 7″ for trailering and to fit in a standard marina slip. The swing wings can function whether the boat is afloat or on a trailer, so they are handy when launching or landing at a crowded boat ramp. The swing wings don’t require any hardware beyond nuts and bolts, and have an advantage over the hinged akas: there’s no need to lift an ama and set it down gently on the vaka. The Seaclipper 16 can be built as an open-cockpit cruiser, or as a daysailer with a tandem cockpit, with the helmsman sitting in the aft position, legs straddling a centerboard trunk and the crew sitting forward. The 7′-long open cockpit has side decks between the akas that offer more options for seating, moving around while under sail, and sleeping aboard while moored.

John Marples, designer of the Seaclipper 16 and builder of LIMONADA, goes for a sail on the Mystic River.

L IMONADA, as an open-cockpit version of the 16, has a daggerboard deployed through a slot in the cockpit sole. A softwood stick wedged in the slot keeps the board down; it has a loop of line at its top for quick removal and raising of the board. The cockpit sole is high enough above the waterline that any water coming into the cockpit drains right out. The rudder is mounted on a false transom, hinged at the top, that allows the rudder to kick up when meeting an unexpected shoal or to be retracted when coming ashore. The downhaul at the bottom of the false transom leads to the cockpit for easy operation. The rudder blade is balanced and has enough of the blade ahead of the pintles and gudgeons to lighten the load on the skipper when coming about. It also allows the arms of the rudder yoke to be short and unobtrusive. The lines from the yoke lead forward to pedals in the cockpit to for hands-free steering. A tiller above the yoke allows steering while sitting on a side deck and is the means of raising the rudder when coming ashore.

A hinged false transom allows the rudder to be kicked up. The tiller pulls the rudder up and holds it. The line at the bottom of the false transom holds the rudder down while the boat is underway.

The Seaclipper 16 is designed to take a Hobie 14 sailing rig. The pivoting aluminum mast, roller-furling jib, and fully battened mainsail are readily available from a wide network of Hobie dealers and may be found used in online classifieds. The Hobie 14 has a beam of 7′ 8″, so the Seaclipper 16, with a beam of 11′3″ can take better advantage of the 146-sq-ft sail rig without flying a hull to the brink of capsizing. Dyneema shrouds, secured to bridles spanning the side decks, support the mast. The plans include specifications for an unstayed wooden mast. For auxiliary power, a short crossbeam aft of the port aka serves as a mount for a small outboard.

The side decks provide seating when two are aboard, and the steering is then done with the tiller, not the foot pedals.

I had a chance to sail LIMONADA, the Seaclipper 16 built by Marples for Mac MacDevitt, on Mystic River near Mystic Seaport. Stepping aboard, I got my first lesson in the values of a multihull. I didn’t have to lunge for the centerline as I do with my monohulls to keep them on an even keel. The trimaran has plenty of stability no matter where I put my weight and the amas (outer hulls) have enough volume of to support my 220 lbs. Without having my movement aboard the boat restricted by the nagging demands of a monohull, I could wander around the boat. The decks are all flat, so the footing is good everywhere. While I like the sweep of a curved sheer line, the Seaclipper’s flat decks simplify the construction of the boat and provide the geometry required for the swing-wing akas.

The deck surrounding the cockpit is large enough to set up a tent for sleeping at anchor. The windsceen was added by the builder to block spray when sailing a brisk breeze.

The deck surrounding the cockpit is large enough to set up a tent for sleeping at anchor. The windshield was added by the builder to block spray when sailing into a brisk breeze.

I liked being able to walk around the boat while it was under sail with Mac at the helm. I never get to see my own boats moving through the water, so stretching out on an ama to watch the vaka’s bow at work was a treat. The 7′-square deck around the cockpit offers a place to pitch a tent. Mac has a two-person tent with an oval hole in its floor to match the cockpit opening. He can sleep to one side of the cockpit, sit comfortably upright with his feet in the cockpit and have access to the gear stowed there. The amas and vaka offer plenty of room for cruising and camping gear; commercial plastic hatches offer access.

I took LIMONADA out by myself and enjoyed steering with my feet and having my hands free to manage the sheets. Nestled down in the cockpit on a padded seat with a backrest, I was very comfortable and relaxed. The sheets were right in front and could be cleated off, making sail-handling a breeze; there was no need to switch sides or do-si-do with a tiller when coming about. During my outing the weather was warm and the wind was light, perhaps 8 to 10 knots at best with a few gusts, but in a cold wind, being mostly below deck level would be a boon. Mac had made a removable windshield that wraps around the forward end of the cockpit for even greater protection from cold wind and spray.

With Marples and owner Mac MacDevitt aoard, LIMONADA flies the windward ama. The leeward ama still has plenty of freeboard.

With Marples and owner Mac MacDevitt aboard, LIMONADA flies the windward ama. The leeward ama still has plenty of freeboard.

The light wind was more than enough to get Mac’s Seaclipper going at a brisk pace and fly the weather ama. There was no spray, so I stayed dry, and even with the boat moving at a good clip I didn’t notice any water coming up through the daggerboard slot.

I was surprised by how well the Seaclipper could come about. With three hulls in the water, I thought there would be a lot of drag in the turns and that the boat would get bogged down, but the rudder blade and the centerboard have enough area to swing the bow around before the boat loses momentum. I never got caught in irons, but I backed the jib for a moment to hasten the bow’s falling off and the filling of the main.

LIMONADA owner Mac MacDevitt reports that his SeaClipper 16 is “super fun in a stiff breeze.” Here, sailing on Lake Champlain, just south of the Split Rock lighthouse he estimated his speed at about 13 knots. “It was exciting, but I felt safe and secure.”

LIMONADA owner Mac MacDevitt reports that his Seaclipper 16 is “super fun in a stiff breeze.” Here, sailing with a reefed main on Lake Champlain, he estimated his speed at about 13 knots. “It was exciting, but I felt safe and secure.”

Christopher Cunningham is the editor of Small Boats Monthly.

Seaclipper 16 Particulars

Length/15′ 11″

Beam/11′ 3″

Beam, amas retracted/7′ 7″

Draft, hull only/11″

Draft, board down/2′ 7″

Sail area/127 sq ft

Displacement, dry/400 lbs

Displacement, full load/800 lbs

Plans for the Seaclipper 16 are available from Searunner Multihulls for $180.

Is there a boat you’d like to know more about? Have you built one that you think other Small Boats Monthly readers would enjoy? Please email us!

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Comments (2)

Thanks for the multi-hull perspective. Lots of cool ideas.

I’ve been looking. This could be the one!

Comments are closed.

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Cross beams/aka's for a 6m (20ft) trimaran

Discussion in ' Multihulls ' started by Aaron_de , Jun 6, 2016 .

Aaron_de Junior Member

G'day all, I'm building a self designed 6m /20ft lightweight demountable trimaran that separates into 3 sections; 2.4m bow section, 2.4m midships section + 1.2m aft section. Why you ask? I have a steep driveway that rules out a trailer but car-topping the boat is just doable. I have a ute (that's a pickup for you yanks!) which can hold the main hull sections while the rest of the boat, Mk3 Boyer A class cat hulls for ama's, mast and cross beams, is on the roof racks. My 3 questions for the collective wisdom of the forum are... 1. If I were to use unstayed aluminium tube section as the aka's what outside diametre and wall thickness would be appropriate? 2. Same question as above but for carbon fibre tube...? (Ha!Like I can afford it!) 3. What are my alternatives to aluminium/carbon fibre to keep them light but strong? Specifications of the boat for reference... - A class cat 4mm plywood hulls for ama's. Estimated weight is 15-20kg / 33lb-44lbs (I have not weight them as yet, anyone know the weight of these?) - 6.8m 22ft stayed aluminium mast. - would like to have at least 2 people on the tramps at any given time. - estimated mainsail area will be 12sqm / 130sq foot - jib 3.7 sqm / 40sq foot - screecher ? not sure but tack will be mounted on a 600mm prodder - main hull is 6mm ply, EPS foam and fibreglass/epoxy. - estimated main hull weight 100kg / 220lbs. - main hull draft at midships 600mm / 2ft - main hull beam at widest point 603mm - sailing beam 5.5m / 18ft - distance between aka mounts on ama is 2250mm / 7.4ft Thanks. p.s. It's my first post so be nice!

tamas Junior Member

Hi Aaron, I have similar size boat but 4.8m wide when open and a lot more sail area. I used 100mm ally x 3mm wall thickness, it seems very sturdy but I am no expert. The folding system I have is similar to Farriers so it may offer some support to prevent tubes bending under load.

patzefran patzefran

I have just launched my new built Strike 20 Tri. It is 5.10 beam . 5.50 m is very wide beam but you have very low buoyancy outriggers. Mine' are Nacra 5.80 hulls. I use 100 mm OD , 3 mm thick aluminium tubes and water stays. With such a wide beam you need waterstays. On my boat I have estimated waterstays max load was around 3000 daN on main beam. Best wishes Patrick https://www.dropbox.com/sh/wi2pj01emza07lv/AADocN3LlA25DjzdTHe0uM4Ya?dl=0 https://www.dropbox.com/sh/ug32rkrarsn83cy/AACE0uUOSLksidTXjNGY8VURa?dl=0

tamas said: ↑ Hi Aaron, I have similar size boat but 4.8m wide when open and a lot more sail area. I used 100mm ally x 3mm wall thickness, it seems very sturdy but I am no expert. The folding system I have is similar to Farriers so it may offer some support to prevent tubes bending under load. Click to expand...

patzefran said: ↑ I have just launched my new built Strike 20 Tri. It is 5.10 beam . 5.50 m is very wide beam but you have very low buoyancy outriggers. Mine' are Nacra 5.80 hulls. I use 100 mm OD , 3 mm thick aluminium tubes and water stays. With such a wide beam you need waterstays. On my boat I have estimated waterstays max load was around 3000 daN on main beam. Best wishes Patrick https://www.dropbox.com/sh/wi2pj01emza07lv/AADocN3LlA25DjzdTHe0uM4Ya?dl=0 https://www.dropbox.com/sh/ug32rkrarsn83cy/AACE0uUOSLksidTXjNGY8VURa?dl=0 Click to expand...

Further to my initial question here's a rendering of my design which I'm calling the RUDI 6.0. In the graphic I'm comparing scale size of Hobie14 and Hobie16 masts. [/IMG]

For the waterstays I use last generation of Heated pre stretched dyneema. I use twin 5 mm for each waterstay which gives 8000 daN breaking strength. I have also used 6 mm Vectran on the aft beams. Vectran is stiffer but has a lower breaking strength. The attachments are 10 mm bent U bolts on the main hull and 12 mm carbon rod through the aluminium beam at the outrigger side. I need to use very high tension on these stays to keep the platform tight, as my boat is on a mooring exosed to wind, waves and tidal current. Building Strike 20 was a lot of work too ! If you hit your 100 kg target for the mainhull, congratulation. My Strike 20 is about 350 kg total weight. Nacra 5.8 hulls are very heavy, 61 kg each ! Cheers Patrick

Woah! 68kg is definitely much heavier that my A class hulls. Keeping your Strike on a mooring means you get to take her out all the time. Dyneema was my first choice for stays if I needed them, probably use single 10mm diametre stays which will go forward and aft of the aka's to provide fore & aft tension as well as vertical. Do you get a lot of spray in the cockpit from your waterstays? And at what speed? Unlike your Strike 20 my RUDI 6.0 doesn't have a flared cockpit (part of how I can keep the weight down) so the trampolines will extend from the ama to the vaka. I expect anything above 6-8 knots wind I'll be getting wet!

waynemarlow Senior Member

Aaron, you may want to look up the TC601 build thread on this forum and build site http://lwr600.co.uk/TC601/index.html where you may get lots of ideas on build and such. You may also want to read through the thread on small 20ft tri's where the use of an A Cat was widely discussed and some calculations submitted to justify the use of such low volume hulls. I'll be updating the website to include how we have dealt with the beams, they have been really really difficult to get an easy and widely accepted method of building them without having weird looking attachment points to the donor hulls, that is widely available through the world. Sorry no the Farrier method is just too cumbersome and time consuming for the home builder, look more at the SeaCart 26 for inspiration.

Thanks Wayne, do you know the name / have a link for the thread discussing A Class cat hulls?

I think the three threads about under 20ft Tris' have a lot of info ( and also a lot dross in amongst it ) but the main one with mention and figures for the A class was http://www.boatdesign.net/forums/multihulls/t20-new-development-class-39874.html

Some more practical data on 20 ft Tris. Two months after launching and solving some problems on our Strike 20, we sailed yesterday in a decent wind. You will find video here broad reaching around 15 kt : https://www.dropbox.com/s/6uk10p6q6jx85qn/VIRB0082.MP4?dl=0 Top speed was 16 kt, with 14.8 mean speed over 500 m and 14.3 over a nautical mile. Patrick

Hi Aaron, Here is a blog I did on the build. http://husky6.blogspot.com.au/ I have been sailing for a couple of years now. I have since added a bit bigger jib and fat head main taking sail area up to about 27M2 which seems to have turbo charged it. I think I am just under 300kg, boat weight. Cheers

Hi Tamas, Your boat looks very nice, congratulation. What is the maximum beam ? I think my Strike 20 is around 350 kg, as the Nacra hulls are very heavy. You should be as fast as me (see my last post). Have you any recent GPS record ? Patrick

Doug Lord Flight Ready

Aaron-here is a thread with many tri's 20' and under: http://www.boatdesign.net/forums/multihulls/small-trimarans-under-20-a-43650.html

LVL Crossbeams

Arched Or Flat Crossbeams ?

foldable cross beams...

Nicol Tri - Alloy Lattice Crossbeams

Normon Cross Trimarans

Cross Beam thoughts for small Tri

Aluminum catamaran cross beam height

Hull flexing on 49' Norm Cross Tri

Building hull in cross sections

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Adapting a weta trimaran for solo dinghy cruising - josé carlos sánchez.

January 14th, 2019

Gijón, Asturias, Spain.

"Weta is made for speed" and it is a compact and light trimaran. Besides tris are stable platforms that can offer the most comfortable sailing. So, you have it all. Just control your speed in all winds and inhabit the boat.

1 Reefing One or two reefs can be installed on the dacron mainsail. Copy the original aluminium plate for the mainsheet hook (2--3mm alu sheet and some inox bolts). You will be able to face winds from F1 to F5, go fast or slow, reduce splash, maneuver in harbor, go trolling, take pictures, etc.

2 Oars 160 cms. oars can be rowed without hitting the amas and can be stowed under the outside crossbar of the trampolines, where they do not bother at all. They can be used as long paddles as well. The "rowlocks" are simply bungee cords attached to the aft aka. Rowing position can be on knees or seated on a traversed board. Rowing the Weta has limited effectiveness: oars are short, the position is not centered and it is difficult to progress against the wind.

3 Outboard bracket I designed this one because it only needs to drill one hole on the Weta´s fiberglass. It can be installed in less than a minute, does not interfere with sailing and does not load the boat too far back. Wood is not a single block, it covers an internal steel frame.

It is worth considering to install an electric outboard if your local conditions allow it. It will reduce pollution and you will not suffer noise and gasoline smell.

4 Stowage 4.1 Inspection hatch . Weta´s standar inspection hatch is too narrow. A 200 mm aperture hatch is wide enough to put ten--liters drybags inside the Weta´s cavernous locker. Mine is a Barton 40081 hatch. A bit wider could be even better.

4.2 Ten liters drybags . Six units of these drybags can stow almost all the gear for 2--3 days (sleeping bag, tent, food, water, stove, spare clothes, anchors, fishing gear, cameras, electronics...).

4.3 Headlamp support. A hook attached to the fore bulkhead can be used to tentatively hang up a headlamp to illuminate the locker. It will be useful not only at night.

5 Chest Made of 4mm plywood , it stows a lot of items you need instantly. Its two upper doors do not interfere with the tiller. It is portable and lets the water come out.

6 Bed The central cockpit is a comfortable niche to put your sleeping bag. It only needs to be dry.

6.1 Bulkhead. A wooden bulkhead adjusted with precision to de cockpit inner shape prevents to a large extent water entry. Adjust it tightly to the boat´s shape (save the Weta gelcoat with a plastic sheet and adjust the shape by using polyester putty). Add some neoprene, rubber or foam tape on the edge to seal any gap. I put the bulkhead right in front of the chest (not showed in the photos).

6.2 Plastic sheet. Now you can extend a plastic sheet (1.8 x 2,5 meters approx) to cover all the cockpit and the bulkhead, and make a dry "nest". Make sure there are no holes on the plastic sheet.

7 Tent A pyramidal tent fly can be hoisted by the mainsail halyard and fits the "round" surface of the Weta decks. Mine is a chinese "Flame´s Creed" 2--3 people hexagonal pyramid tent (bought from Aliexpress). A row can be used as a pole to plant the complete tent on the ground.

8 Stove The Trangia 27 stove fits perfectly into a 10 liters drybag and goes through the 200 mm inspection hatch. May be you can even make a cofee while (slow) sailing.

9 Anchors 9.1 Bottom anchors. The 200mm inspection hatch is wide enough to stow proper anchors for the Weta (I carry a 2.5 kgs. folding Grapnel and a 3.5 kgs. Britany).

9.2 Floating anchor. It is a must to be able to stop the boat on the water, face to the wind, to reef/hoist the mainsail.

10 Daggerboard case reinforcement Made by adding strong epoxy putty to the rear union of the daggerboard case to the hull. Just in case. Epoxy putty is incredible strong once hardened. I am not sure about what would happen but I would prefer to break the daggerboard...

11 Miscellaneous Auxiliary stay to raise the mast . It permits to raise the mast by one person without risk of falling. Once the jib is installed, the auxiliary stay can be attached to the base of the mast. It will be used again to lower the mast.

Jib halyard quick tensioning system

Halyards bag

Stowage of the halyards inside the upper mast Having the halyards in place saves a lot of time. They can be stowed inside the upper mast. A bungee cord set them secure and tight.

Long rope and open climbing blocks to recover the boat whatever the situation you face (slope, sliding floor, mud...). Much better if the car does the traction although you can do it by hand as well. The complete kit remains in the car. You will also need a trolley front wheel.

Trolley front wheel

Long items storage. Use the amas to stow your rods or long items. Tie them to prevent they go out of reach.

Rod holder This one fits into an aluminium tube (mine is from an arrow shaft) attached with duct tape to the "leg" of the rear aka.

Hope giving some help Happy Weta cruising! Jose Photo album here

Weta Trimarans

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Farrier International

a Division of Daedalus

FARRIER FOLDING SYSTEM™

One key to the success of Farrier trimarans is the easy trailerability made possible by the unique Farrier Folding System ™.

The Farrier system is the most structurally sound trimaran folding system available, with no hinges in the beams or the critical beam to float join, while corrosion prone wires are never used in structurally critical areas. Overall beam can be varied in seconds, by just one person, anywhere.

After 33 years of use world wide the Farrier System is well proven, the most successful folding system, and used by more trimarans than anything else. So to be safe, be sure to insist on the genuine twin strut ‘Farrier Folding System’™. It is significantly different from all the rest, and the many advantages can be summarized as follows:

Folds for road legal trailering in minutes without any heavy assembly being required.
The twin strut folding system gives absolute control over movement
No need for water to support floats while folding – the twin struts make it easy to fold anywhere
The correct folding strut geometry means folding can be done by one person, anywhere.
Twin struts mean the float will not fall on the ground if folding out of the water on a trailer
Absolutely no weak hinge points in the actual beams, with the highly stressed beam to float join being solid
Absolutely no sliding parts that can bind or jam
Corrosion prone wires are not used in structurally critical areas where sudden failure could threaten the boat
The structurally critical lower struts are solid Aluminum 6061 T6 bar, with absolutely no butt welds.
Custom made reinforced acetal (plastic) bushes insulate aluminum struts from stainless steel pivot pins
There is no reliance on the rig for structural support should float reverse loading occur
Beams are structurally sound no matter how loaded, including even after a capsize
Proven track record, with 33 years development, six Atlantic crossings and race records/wins world wide.
Now used by over 3000 boats world wide

Folding System

Legendary ability, unbeatable reliability.

Folding and unfolding a Corsair trimaran takes only a minute. With just 4 bolts to remove, it is easily managed by one person, and is normally done while afloat. Simply raise (to fold) or press down (to unfold) the inboard end of one cross beam. It can be done from the safety of the cockpit and only a little force is needed due to the folding system’s carefully balanced geometry, and the movement of the floats being mostly horizontal.

The solid aluminium folding struts have absolute control over the folding motion and prevent flexing or racking. A stainless steel bolt on the inboard end of each beam secures the floats for sailing. Crucially, wingnets remain attached during the folding process – their frictionless fixing allows them to tension themselves appropriately through the folding process. The system is so simple and balanced that Corsair trimarans can even be folded while motoring.

TRAILERING ACROSS CONTINENTS

Corsair Marine trimarans are especially weight-conscious, and sit low on their trailers meaning they have excellent trailering characteristics. They are equally easy to launch, giving you more time on the water, and the ability to expore many more remote cruising grounds or participate in regattas far from home. Some Corsair trimaran models go from trailer to water in 25 minutes, and with practice even the largest boat models can be done in 40 minutes.

Corsair 880 Trimaran | 2022 Boat Review by Multihulls World

Corsair 880 – Drive Out, Fold Out, Thrill Out, Chill Out

Australian Debut of the Corsair 880 at the Sydney International Boat Show

Folding Corsair Trimarans: Legendary Ability, Unbeatable Reliability
5 Reasons Why The Corsair 760 Trimaran Won Multihull Of The Year
Corsair Range Brochure
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Review of nine small, folding day-trimarans (2010)

by mike waters n.a.

As much as I like the basic concept of Jim's new boat, there are a couple of aspects that I need to mention. To put a light rig from a Hobie 16 on a boat that is FAR heavier and more stable than the boat for which it was originally designed, might prove too much for this mast, especially since the shrouds are more inboard than normal—so raising the mast compression. Normally, a Hobie would just 'go over' and so relieve the load—but not this beamy 800 lb twenty-footer! Also, the too-typical, puny 4-oz sail cloth of a regular Hobie 16 sail, is hardly man enough for this job. It's certainly a low cost start up solution and we've all admired Jim for his support to those with lesser means, but I think any builder should plan on something more substantial to be a better match for this cruiser. Finally, as the ama looks to be quite substantial in volume (guessing about 800 lbs buoyancy?), I have some concern for the strength of the single plank akas (cross beams) that act as swing arms for folding, should the builder decide to choose regular construction lumber. Sooner or later, someone will push this boat hard enough to bury an ama and that's a LOT of leverage on those arms, even if they are cleverly designed to act like huge flexible wooden leaf springs. But without seeing the details, I can only suggest that some good laminated material might be in order for these parts and perhaps Jim's plans already call for that or even some added carbon here as well. But I like the general concept and even though the boat will be no speedster, it's a design that can give a young couple on a small budget, a lot of weekend pleasure provided the conditions are within what the rig and swing arms can take.

This particular Performance Index is simply a product of the principal things that affect multihull performance (LOA × BOA × Sail Area) all divided by the listed Weight. By taking the square root of this value, you then get a figure that very roughly reflects speed for comparison purposes. Yes, I agree there are a lot of factors NOT taken into account with this crude approximation, but the base figures used are easy to find and at least the general trend is indicated—and quite fairly so I believe.

TRIKALA 19 The Trikala 19 is from the board of imaginative designer Kurt Hughes. This boat was actually in production for a while in Spain but since then, a few have also been built by amateurs. A couple reportedly even cruised the Mediterranean in one! This is a boat design that always frustrated me—perhaps wrongly so.

For me as a designer, the looks of a boat are almost as important as its performance and the Trikala looks quite stunning from the bow, with its long fine entry and streamlined deck lines. But then, as it opens out to encompass a very wide cockpit aft, it always appeared to me that something distracted the designer or he just lost interest, as the view from the stern quarter is not so elegant. It's no doubt practical but it's a shame that its wonderful efficient appearance from the bow could not in some way be maintained at the stern. But with that very personal comment aside, this is an interesting boat with no doubt a good performance. It would be a particularly interesting boat to build for someone wanting to learn about composite construction with a larger boat in mind 'down the road', as the Trikala is lightly built of foam core under fibreglass skins and would therefore provide a good learning experience. The boat does not fold in a conventional way but like some other small designs by Kurt, uses a sliding system with tubular akas, the port ones, sliding into tubes with Teflon runners behind the starboard ones—so the two sides are not exactly symmetrical—a factor that some potential buyers find disturbing, though the difference is purely cosmetic. (The larger 7 m, L7 by Mike Leneman, also uses a similar sliding system – though in this case he uses fiberglass channels—see my REPORT on SMALL TRIMARANS for more on the L7, available through my website.)

W17 This design of mine was created during 2009 and completed in 2010. It's hard to review your own boat designs without being accused of inevitable bias, so I will simply tell you about it and point out the features I've incorporated and why. However, time has now shown [2020] it's as good as I had hoped and expected her to be.

This is a primarily a boat 'to just enjoy sailing in'. She's designed to be comfortable, way drier than average, fast and efficient and is just at home on a weekend camping cruise as on the circuit. With several boats now [2020] having each sailed and cruised over 1000 miles and with open sea passages of up to 60 miles safely accomplished, she is certainly proving very capable in experienced hands, employing intelligent sail reduction when things get rough. Her seemingly simple hull forms give a very high efficiency and she has proven quiet and dry through a chop and with her wing mast and unique ama shape, shows an unusual ability to climb to windward with minimal leeway. [Following an independent test and review by Wooden Boat Mag., I was asked to explain why the W17 performed so well with such simple shapes and my reply to this was published in the prestigious Professional Boatbuilding magazine #169 .. and is available to read on this website under 'Published Articles'].

Sailing this boat is indeed a magical experience and dozens of boats are now (2020 update) being built in over 30 countries. She's a little more time-consuming to build than others her size, but numerous owners have since dubbed her, 'The Miata of the Seas' . For them, a few more hours is well worth the effect and this boat will take you to a whole new level above any production boat of this size out there .... and also cost you less.

Comparison Chart (created in 2010)

The Microship Substrate

by Steven K. Roberts Nomadic Research Labs

One of the driving requirements of any project is the need to minimize the nightmare of fabrication (unless that process is amusing for its own sake, which is certainly a valid approach). But basically, I believe that life is too short to re-invent the hull, and frankly, if I could have found an off-the-shelf boat that met my needs I would have engaged in epic schmoozing or similar aberrant behavior to acquire a pair of ‘em. We actually tried this twice (with the Fulmar and Hogfish ), but the lack of clear project specifications doomed both to failure. There’s a lesson in there somewhere.

OK, if we can’t just go get a Microship, how do we get close? Real™Designers think nothing of conjuring a set of lines, scantlings, and fiberglass layup schedules to address a client’s needs, although these tend to be people who make a career of marine architecture and are not intimidated by the process. But building molds for hulls and designing internal rib structures just to get something that floats, before even starting on the “interesting” parts? Naaah. Not at Nomadic Research Labs—that sounds too much like work. As such, the first few weeks of this project (once we arrived at a clear design goal , which took five years) involved the quest for existing hulls and anything else that would let us avoid Big Nasty Goo Jobs.

Fortunately, people have been making highly efficient, slender boats of suitable scale for a long time… they’re called canoes .

The Center Hull

The objective here was easily stated. I wanted maximum volume in a smooth, hackable hull, tough enough to withstand occasional abrasion and long enough to provide a center cockpit area with room to lay my lanky 6’4” body down to sleep.

The hackability requirement called for a hull material that would accept epoxy and thus allow added fiberglass structures, ruling out canoes made of plastic, aluminum, or any of a variety of vinyl/ABS/foam-sandwich materials designed to take river-running abuse and provide absolute flotation in case of flooding. A search of available products in the 18-20 foot range turned up a number of vendors large and small, and for reasons of specifications and aesthetics I found myself gravitating to Wenonah . Before long, two of their excellent “Odyssey” expedition canoes were enroute to the West Coast from the company’s plant in Wisconsin.

The boats were slightly customized by the manufacturer to accommodate our unusual needs: we had no use for the usual canoe seats, thwarts, or gunwales, but Wenonah bonded in a pair of 1/2” marine-plywood bulkheads eight feet apart—coinciding with the distance between the crossbeams of a stock Fulmar 19-foot trimaran. Why was this dimension relevant? In parallel with the canoe quest, we had discovered to our delight that we would be able to purchase outer hulls and crossbeams from Fulmar Canada, shortly before their discontinuation of the product. Not only did this save another huge load of work, but it freed us from having to come up with this dimension ourselves through some arcane combination of marine architecture and rectumology. There would be quite enough inspired guesswork over the next few months anyway, and it’s nice to reduce the number of variables up front.

Stock Wenonah Odyssey Canoe Specifications Weight: 42 pounds, with Kevlar ultralight construction Length: 18.5′ Rocker: 0” (this means the bottom is flat from bow to stern) Depth (bow): 20.5″ Depth (center): 13.5” Depth (stern): 16” Max Width: 35” Waterline Width: 32.5” Gunwale Width: 34”

The Odyssey hulls gave us an ideal starting point for the project: a lot of interior space in a smooth, lightweight package. In principle, all we had to do to turn them into trimarans was attach the Fulmar parts, a task that for a few exhilarating days was little more than a single line-item on the To-Do list .

The obvious problem is the physical interface with the crossbeams and outer hulls, but we also had to make some early decisions about the design waterline (the line that designers optimistically draw on a boat to demarcate topsides paint from bottom paint), freeboard (how far above said waterline the gunwales are, affecting everything from windage to the dryness of the ride), centers of gravity and buoyancy (ensuring that the boat tends to float in such a way that the waterline turns out to be correct), dihedral (how high the outer hulls should be relative to the center hull to strike a balance between dragging heavily in the water and tipping annoyingly from side to side when at rest), and balance (the overall relationship between stuff that gets blown around by the wind and stuff that hangs under the boat, ultimately manifesting itself in the feel of the helm and general sailing performance). In other words, having a pair of canoes in the lab, perched inscrutably on workstands, failed to reveal an immediate and obvious next step. But at least we had a lot to think about.

Inevitably, much of the noodling that goes on in the early stages of a design is a bit painful to relate. If you recall the spirit of the engineering process discussed in my Gonzo Engineering piece, you know that it takes the form of tossing all the variables into the air, juggling them frantically while studying their interactions and bothering experts with dumb questions, then confidently congealing them into a clear mental model that has to be correct—or appears so until the one expert you were unable to reach finally returns your call and says, “What? No, no, you can’t do it that way; jeez, who on earth told you that?”

OK, maybe I’m exaggerating a little, but I bet if you drag a system architect out to a pub and start the beer flowing, you will eventually extract the admission that any new design involves a healthy measure of unquantifiable art and wishful thinking, stitched together by formal tools and guided by the intuition gained through a lifetime of design work (all adding up to unshakable opinions about what’s right). That’s pretty much what happened here, and in the early phases I depended heavily on others for many of the marine architecture essentials while my job became one of research, synthesis, and conflict resolution; essential wizardry at this stage came from the formidable talent pool of Bob Stuart, John Marples, David Berkstresser, Gino Morrelli, Greg Jacobs, Mark Reynolds, Jim Antrim, Andrew Letton, and a few others.

With such cognoscenti contributing ideas, how could we possibly go wrong?

Gunwales and Bellies

It was obvious from the beginning that the center hull would need more freeboard than was provided by the stock canoe, so we decided to make the boat 2” taller all the way around. This adds internal volume and makes for a drier ride; it has nothing to do with the waterline or buoyancy.

You can see the details of this and some of the other “first steps” in this photo. Up near the bow, Bob Stuart is trying to establish a vertical line for the placement of the mast step (getting a level reference plane is a real pain in a boat, because everything is curved). In the foreground there is a molded aka nest resting atop the aft bulkhead, with one of the crossbeams nestled inside. We’ll discuss this in the next section.

Along the top edge of the boat there is evidence of a bit of surgery in progress, detailed in the drawing below. When the canoe arrived in the lab, the rim of the hull ended with the little square cross-section labeled “original wood gunwale”—less finished than would normally be the case, as we knew we were going to hack it anyway. The single-layer wall below that is a thin layup of Kevlar plus an external gelcoat layer (a tough pigment). Every 2 feet there is a stiffening rib of foam-core material that curves from the gunwale down to join the canoe floor, which similarly consists of two skins separated by a thin layer of foam. The net effect is a nice balance of lightness and rigidity, and we tied into it with all of our subsequent construction.

Here we are looking edge-on at our new additions to the gunwales. Below the original wood, we glued in a tapered piece of foam (ripped on a table saw) to allow our added fiberglass cloth to lay smoothly along the hull, as it refuses to bend around sharp corners. Above the wood, there is a 2-inch wide strip of foam, and directly to this is glued the deck, made of identical stuff. Where these two pieces meet (at slightly less than a 90° angle, given the slight crown of the deck for drainage, stiffness, and aesthetics), we sanded the outer corner to a gentle radius and, inside, added a fillet of thickened West System epoxy with the consistency of peanut butter. At this point, all we had to do to make it strong was cut some pieces of fiberglass cloth, lay them on all the surfaces, and squeegee on the epoxy.

The internal view of the resulting structure is shown here, looking forward from inside the front hatch. There are actually a number of details revealed here. Beginning up at the deck (ignoring the hardware and black hydraulic line—that’s part of the landing-gear steering assembly), you can see distinct levels as you move down along the sides of the hull. Starting at the horizontal underside of the deck, there is that 2” tall strip of foam, then the original wood rim, then a different color of foam used for the tapered part. Why different foam? As with most materials in this business, there are lots of options; here, we had less need for compressive strength so we used a lighter material to save a few ounces. The final stratum visible is the overlap of fiberglass cloth onto the original hull material.

Incidentally, those two wooden strips on the sides of the hull are for added stiffness—we were concerned that sailing would subject the boat to much heavier cyclic abuse than originally intended, and these reduce any tendency that the large flat surfaces might have to flex (or “oilcan”) in response to waves. Also, in the foreground of the photo, you can see one of the foam-core stiffening ribs I mentioned above.

At this point, we have a canoe that’s 2” taller than before, and have also established how the deck is integrated with the hull. If we were simply closing an open boat and adding a few compartments for gear storage, we’d be nearly there… but this is a Microship, which obviates simplicity. A simple decked-over hull with access hatches is fine for the bow and stern segments, but the region between the bulkheads is a different story.

Here, we have to accommodate a gadget-happy human with as much space as possible, provide horizontal surfaces in the cockpit for armrests and controls, support the equipment console, install the retractable seat and other essential fixtures, allow room to sleep, and somehow segue into vertical walls that provide inboard support for solar panels. All these needs are addressed by the structure shown schematically in Figure 5-5, which became known as the gunwale belly.

Starting from the bottom, we see the same structure that appeared in the basic bow and stern sections—the pair of foam strips that add 2” of height and let fiberglass cloth lay nicely against the hull. But instead of merging into a simple deck, these now tee into long curved foam sections, running the full eight feet between bulkheads. After considerable experimentation, we discovered that the Divinycell core material will easily take simple curves through a carefully calibrated thermal process involving industrial electric strip heaters and a bending jig of 4” PVC tubing to provide a consistent radius. In retrospect, it would probably have been better to bend longer sections at once than we did, as the minor variations in the process translated into a lot of sanding and filling later, but such is the nature of prototypes.

You can see the results below. Closest to the photographer is the opening for the aft gear hatch, and the gunwale bellies adjacent to that are thicker than the rest—2 inches, to be exact. These are the “roots” of the arch structure to be added later, providing support for a fabric enclosure reminiscent of an automotive convertible top, as well as mounting space for all sorts of essential equipment. The little foam triangles between the arch roots and the hatch opening will provide surfaces for the electric thruster (port) and the anchor (starboard); the different foam color, as before, is because we didn’t need as much compressive strength in this area.

Just forward of all that is the aft aka nest, and as that’s the subject of the next section I won’t say anything about it here. Continuing in the same direction, we come to the cockpit area itself—a huge opening flanked by those segmented gunwale bellies (still raw Divinycell foam, not yet fiberglassed. Now you can start to see what they’re good for: once the seat is installed, these horizontal surfaces, or decklets, end up becoming a significant part of my immediate environment, much easier on the arms than the original thin canoe gunwales. The big rectangular hole on the starboard side will become part of the trunk that houses the pedal drive unit.

Note the horizontal flat section just forward of the open cockpit space. This is the floor of the equipment console area, which will be packed with computers and communications gear. Just below it, you can see the forward bulkhead (where the battery box will go), and the last visible feature before we reach the limits of the cheesy flash on that clunky first-generation 640×480 digital camera is the forward aka nest. If you squint at the picture just right, you can also see a black object that appears to be atop that—that’s the mast step, which we’ll get to shortly.

It’s funny… it all seems to go so quickly when I write about it like this. One might be tempted to conclude that construction proceeded just as smoothly. But in these early stages, we were faced with the problem of accommodating all future needs, some of which had barely been articulated. While certain features were defined by the chosen hulls and crossbeams, we were still vague on a few details; all I can say is that it’s a good thing fiberglass and foam are so editable!

OK, let’s look at those critical hull-crossbeam interface widgets.

The Aka Nests

You’ve seen them already in the photos above. The task here was to take a pair of curvy crossbeams designed for a small commercial trimaran, and somehow graft them onto a canoe. There are no off-the-shelf brackets that do this, and crudely bolting them on without thinking about stress distribution would be asking for premature failure. The solution was to mold custom nests.

The crossbeams from the Fulmar are U-sections, meaning that they are open at the bottom. To mold a perfectly mating shape, we had to box them in with something flexible, yet stiff and smooth—scrounged Formica countertop laminate from the dumpster of a nearby cabinet shop turned out to be perfect. We simply cut strips on the table saw and hot-glued them to the crossbeams, as shown in the cross-sectional drawing:

For this to work as a fiberglass mold, there are a few requirements. First, since the fabric will absolutely refuse to wrap around square corners, it is necessary to radius the outside corners and fillet the inside ones. We carved the radius with a laminate trimmer (basically an agile little router), and immediately ran into the problem of removing so much of the thin Formica material that our glue joints started to fail. We changed to a tighter radius and got it to work with more aggressive gluing, realized that at least the first few fiberglass layers would have to be on the bias (with the weave at a 45° angle to the edge, allowing it to make a sharper bend). The fillets were easy—filled epoxy applied with a tongue depressor and sanded smooth. Finally, the whole contraption was given a few coats of mold-release wax, ensuring that the new layup would not become a permanent part of the crossbeam… we do need these to be removable!

Adding cloth is time-consuming but straightforward. Each nest was given 6 layers of 10-ounce cloth, yielding a final thickness of about .060”. (Additional strength would be added where needed later, during integration with the boat.) We kept the process flowing, allowing each layer to gel a bit before adding the next, thus ensuring a good chemical bond.

After final cure, we popped the parts off the molds, a process that is always, for some reason, incredibly satisfying. The waxed Formica surface left a very smooth interior finish, and all that remained was cleanup of the ragged edges prior to bonding them to the hull.

Somewhere in here, a rather large question arose: where, exactly, do these things go ? Their distance apart was defined by the existing Fulmar aka/ama assembly, of course, but the variables included fore-aft placement of the whole affair, height above waterline, and amount of pitch-axis tilt relative to the center hull. This called for many hours of staring, sketching, and calling experts; we finally concluded that it should go, yes, right about here . As with many such decisions, what looked and felt like a SWAG (scientific wild-ass guess) was actually built upon a lot of research, but this was one of those areas where verbal explanations from marine architects carried more weight than objective measurement of waterplane areas and angles of attack.

The nests were glued in place using the whole aka/ama assembly as a fixturing aid, then gradually accumulated layers of fiberglass that rendered them permanent parts of the boat. The only remaining issue was the attachment method that would allow easy removal of the crossbeams.

If you think about the “load case analysis,” it’s clear that across most of the nest there is actually very little stress. The real action happens where the crossbeams meet the hull, and almost all of that stress occurs when the boat is fighting heeling forces from the wind in the sail (recall that the wind is often doing its best to push sailboats over, and a trimaran fights this influence through the buoyancy of its outer hulls instead of the mass of a keel). While this is happening on one side, the other is just supporting the weight of the outer hull, insignificant by comparison. In other words, we really need to be able to deal with high intermittent tension loads. This all translates into 3/8” stainless bolts bonded into a relatively incompressible wood-core substrate well-glassed to the surrounding structures, poking through the top of the crossbeam, and captured with acorn nuts along with something to distribute the load and avoid crushing glass fibers.

There comes a point in boatbuilding whereon the vessel starts to appear as one lovely thing instead of thousands of bits of foam and glass all glued together in a patchwork of multicolored fillers and epoxies. We’re not there yet in this discussion, of course, but this sneak preview should give us hope, while clearly showing the top view of the aka attachment:

While we have that photo to look at, let’s talk for a moment about the distinctive square structure behind the seat. As Microship design progressed, it became ever more apparent that there would have to be a way to define an enclosed cockpit space more substantially than with a rickety folding frame of metal tubing, as is often used to support the fabric dodger or bimini on small cruising vessels. A decent integrated structure would offer a lot of advantages: mounting space for cockpit fixtures (you can just barely see the face of the Marine VHF radio in the photo), support for an antenna and radar reflector as well as the stern navlight, and—perhaps most significantly—a substrate for a traveler that allows the point at which the boom is sheeted to be moved from side to side, giving more control over sail shape and angle to the wind. That is the horizontal rail-like object atop the arch, and that wonderfully arcane vertical thing in the foreground is a dual-band J-pole antenna for amateur radio.

From a fiberglass perspective, the arch is a direct outgrowth of the deck, though we used a very lightweight blue insulation foam, sculpted it into a pretty shape, and laid on the glass. In retrospect, we probably should have chosen a proper structural foam like lower density Divinycell, for the cheap home-improvement stuff crumbles and cracks at the slightest provocation, making subsequent thread-casting and other retrofit jobs a pain.

Near the bottom of the arch, you can see a little horizontal step with a pin sticking up; that’s part of the solar array mounting system.

Decks and Hatches

During our discussion of gunwales and bellies, we saw how the half-inch foam core was glued at an almost-right angle, then rounded, filleted, and glassed over to make a smooth hull-deck seam. It’s only simple at the forward and aft ends of the boat (about five feet each), but these are very critical areas for mounting surfaces, aesthetics, and the gear hatches. Where else, on this tiny vessel, would I put all my junk?

To achieve a nicely crowned deck, a big flat piece of stock Divinycell foam was constrained in a fixture to induce a simple curve, then glassed on both sides. The tensile strength of the fiberglass is more than enough to retain the shape with just a wee bit of spring-back, so no thermal bending was necessary (unlike the extreme curves of the bellies). Segments of this were then cut out to create the foredeck and afterdeck surfaces, and the hatch covers were made of the pieces left over from carefully cutting the openings that they would cover. There’s a good view of this in this photo, which documents one of those long days of sanding, sanding, endlessly sanding.

We spent a long time pondering the hatches, addressing the basic practicality of providing useful stowage space and the daunting problem of keeping the contents dry… even when green water aggressively hammers the foredeck while I’m out flirting with death instead of spending a storm day safely in camp. I confess that I was tempted by off-the-shelf “opening ports” from the marine supply world, but they are heavy, expensive, and the wrong shape. Most are also designed to be opened from the inside, as apparently, on some boats, there is actually enough room to move around below. Fortunately, I was talked out of this by Bob Stuart, who is less intimated by tricky fiberglass projects than am I.

The hatch covers are deceptively simple. The opening in the deck has a flange that projects upward all the way around the cutout, forming a coaming. To create this, a strip of newspaper was soaked with epoxy, allowed to stiffen but not fully cure, then wrapped around the raw edge of the hole. Once this solidified, it formed a tidy little core for the continuation of both top and bottom layers of fiberglass covering the deck.

You can see a cross-sectional sketch of this above, and this is the result— showing the flanged hatch cover kevlar-tethered to the boat. These index nicely together, of course, leaving only the problem of waterproofing. That black ring around the hatch cover is a simple glued-on gasket of neoprene (a Silicon Valley dumpster-diving treasure), which makes a good seal when mated with the sharp edge of the deck flange.

Unfortunately, this still doesn’t finish the job. Something has to hold the hatch cover down tightly enough to achieve gasket compression, and this part is a bit sub-optimal. One of the fundamental lessons I’ve learned from early tests of this system is that anything that involves fiddly loose parts is going to be a headache. This approach is pretty; the 1-inch tubular nylon webbing is sewn to stainless-steel D-rings retained in deck fixtures, which were fabricated through a rather tricky process of laying fiberglass “bow ties” over a mold of thin vinyl tubing (later extracted without difficulty, as epoxy doesn’t stick to such things). The result looks sexy, but in practice Out There it involves too many hands—typically, I’m balancing on those rectangular nonskid pads as the boat dances around from the influences of wind, waves, and dynamic body weight. Meanwhile, I’m trying to hold onto the slippery rotating rig, my arms full of whatever I went up there to fetch… then I have to grip the item(s) of interest under my chin while messing with straps that don’t provide enough gasket compression. In other words, if you’re building one of these, trying to extract enough information from the photos and spaces between the lines to answer all the un-addressed how-to questions, please don’t copy this part. Make your hatch covers captive, operable with one hand!

(If I were doing it again or modifying this for an expedition, I would use an internal hidden hinge, a remote-release spring latch, and the existing water-shedding flange system but with more compliant gasket material.)

In many of the photos seen so far, there has been a visible feature that I have hardly mentioned: a black tube poking through the deck just in front of the forward bulkhead. Affectionately known as the mast urbator , this accepts the 21-foot freestanding rig, which is then free to rotate on its Delrin bearings. Since this glassed securely into the hull we should introduce it here.

The primary requirement in this area is brute strength. If you think about what’s happening in a high wind where all the transient and static loads are concentrated, it’s clear that this has to be one of the strongest places on the whole boat—and it’s no coincidence that this, the forward bulkhead, the aka nest, and the landing gear are all bonded securely into a single structure. The mast step is shown here, viewed from inside the forward hatch.

The unit itself began life as a chunk of aluminum tubing with 3” inside diameter and 1/8” wall thickness. Since this was to be in a nasty environment and a partner in a bearing relationship, we wanted it corrosion-proof and slippery. This called for a special form of anodizing that goes beyond the normal conversion coating used to increase corrosion resistance—this process embeds Teflon in the surface, yielding an incredibly low coefficient of friction, the hardness of steel, and excellent abrasion resistance. Typified by the Tufram process from Magnaplate , this is used in industry where lightweight parts are needed to replace those of case-hardened steel, but without giving up the desirable surface characteristics.

Once we had the part on hand, the task was to fixture it into the boat in such a way that the mast would stand perfectly vertical. In an environment of curves and and imperfections, this involves standing back with a funny squinting expression, mumbling over bubble levels and tape measures, and wondering how something that looks so right can measure so wrong (and vice versa).

In the photo above, you can see the massive layup that integrates this unit into the hull. We ground the fancy anodizing off the tubing where it would have to take epoxy, then subjected it to an aluminum-etch process (Alumiprep) to allow a proper chemical bond to the surface. The fiberglass is in layers, each slightly larger than the last to provide graduated load distribution without any stress-risers. (If there is a sharp boundary between two objects that are enjoying cyclic stress relative to each other, fracture will occur at that spot. This can be generalized to the advice that one should avoid square corners in just about any system subject to flexion, because that is where failure will eventually take place.) Here, we cut out a dozen or so circles of fiberglass cloth, stepped in increments of about half an inch. The result is a smooth transition between the rigid mast step and the tough but flexible hull.

A few details are worth noting here. A vertical tube stuck in a boat is going to fill up with water, so a drain hole was molded into place through the bulkhead into the main compartment. The rationale is that the cockpit is generally wet and has a bilge pump, while the forward gear hatch should stay as dry as possible. Second, since the mast is going to rotate in this thing, there had to be something approximating a thrust bearing, however crude. This took the form of an epoxy-sealed chunk of wood with a hard plastic surface screwed (with recessed flat-heads) on top. This just rests in the bottom of the urbator, and it has a couple of protruding screws to allow easy removal with a loop of string.

In the internal mast step photo, you might have noticed a couple of other features. The white flexible tube emerging from the plywood bulkhead carries a bundle of hydraulic lines as well as a coaxial cable to the VHF antenna on the bow. The cable on the other side is for the navlights and serial data stream from the ultrasonic wind sensor. And the little disc in the upper right corner is a talisman that accompanied me 17,000 miles around the US via bicycle—a St. Christopher medal given to me by a lady in Key Largo, Florida after some rednecks just about killed me. (I’m not Catholic, but you know… it’s not really about that, is it?)

Daggerboard Trunk

For this part to make sense, I should say something else about how sailboats work. To do anything other than coast downwind with the wind astern, a boat needs a way to provide lateral resistance to moving sideways through the water. Given this, the aerodynamic lift provided by a well-designed suit of sails can propel the boat through a very wide range of angles—not directly into the wind, of course, but surprisingly close. 45 degrees is not uncommon.

A monohull takes advantage of its keel to accomplish this; that hunk of lead on the bottom is more than just a big counterweight to keep the boat from blowing over. But if we have a multihull (or a beachable dinghy, or even a sailboard), we have to provide lateral resistance some other way. This typically involves a retractable board, foil-shaped to minimize turbulence, mounted at an appropriate spot in the hull. Some boats use leeboards that pivot down outside the hull, accepting the noise and drag of a “surface-piercing foil” in exchange for simplicity and minimal impact on usable space aboard. Others go for greater efficiency with a centerboard that deploys from an internal trunk, but these eat up precious internal space and can fail catastrophically in a grounding.

We elected to try a quirky compromise in the form of a retractable daggerboard that slides through a trunk at the turn of the bilge—leaving the center of the tiny hull free for sleeping and pedaling while avoiding the splashes and general clunkiness of a leeboard. In this photo, you can see how the daggerboard is forward-angled to increase the probability of harmlessly kicking up in a grounding. (The bow is to the left, and that little fin in the lower right is part of the pedal-drive unit over on the starboard side.)

The weirdest thing about this, at first glance, is the fact that it is angled forward. This was not some dumb mistake from pulling a bleary all-nighter; it was calculated to avoid damage when I plow into something. Assuming the boat is moving mostly forward (not always the case, but one can hope), then the board will just pop up instead of attempting to pivot aft, knifing through the hull and turning an oops moment into a potential catastrophe.

To facilitiate this, we did a little trick to minimize friction. One of the more wondrous materials available from McMaster-Carr is bondable Teflon , chemically treated on one side in a way that makes the ultra-slick PTFE plastic accept epoxy. As far as I know, the only explanation for this is “magic,” but then, I’m not a chemist. In any case, it works beautifully, and whenever we needed tough slippery spots on the boat we just lopped off a suitable chunk of this stuff and glued it on. The trunk, which was molded of fiberglass around the recycled (and heavy) daggerboard from an old Nacra beach catamaran, now has little Teflon inserts in all four corners, and the sliding action is smooth.

Normally, of course, I try not to depend on hitting bottom as a way of raising the appendages. Another nice feature of the forward-angled trunk is enhanced usability: I can raise the board with one hand and park it in a little notch on the cowling. The cockpit perspective on all this is shown here with the dagger retracted, hoisted by a handle made of 1/4” braided line and a scrap of tubular nylon webbing.

The trunk itself is simply glassed into the hull and deck, providing a very stable structure that, like everything on the boat, ends up becoming a mounting surface for something else. That complicated hydraulic assembly is the rudder deployment system, and the gap between trunk and hull provides a nice place to tuck the spare paddle.

So much for the basic trunk fabrication… but there’s one critical issue we haven’t mentioned. How did we know where to put this thing? Does it really matter?

As it turns out, placement is absolutely critical. One of the many delicate balancing acts involved in sailboat design is the relationship between the center of effort (CE) and the center of lateral resistance (CLR). Screw this up, and the boat will become hard to handle, inefficient, and possibly even dangerous.

CE can be viewed as the resultant center of all the wind’s effects on anything above waterline. Obviously, this is mostly about the sail and is thus a function of conditions, but it is also significantly affected by the topsides, the arch, whether or not the dodger is deployed, laundry flapping from the antennas, courtesy flags and burgees … whatever. Somewhere up in the air over the console is a magic point that represents a big celestial finger pushing on the boat.

Similarly, CLR is the resultant of all the stuff below waterline and the drag it presents to sideways motion. Some things, like the daggerboard, are specifically designed to do this effectively, but the tendency to slip to leeward is also affected by hull shapes and the presence or absence of the pedal drive and electric thruster. The rudder is also a huge factor, but we don’t have much choice about where to put it. Daggerboard placement is essentially the only variable that doesn’t involve a lot of extra work.

Why does it matter? Picture this: if the CE is way forward of the CLR, then the boat will always try to “fall off” the wind, or turn away from the applied force and run downwind. Such lee helm can be pathological, because if you are trying to head as close to the wind as possible and for some reason (including inattention) lose rudder control, the boat will turn in such a way that the heeling forces get abruptly higher—stressing the rig and crossbeams, and, in extreme conditions, increasing the possibility of capsize. You don’t want a sneeze or a broken rudder fitting to dump you into a dangerous situation.

Conversely, if the CE is aft of the CLR, letting go of the steering will cause the boat to turn into the wind as the bow is pushed around that virtual pivot point… whereupon the sail will flog and you end up dead in the water, in irons. That may be embarrassing, but it beats hypothermia. It might seem that one would want the CE directly above the CLR, but it turns out that a little weather helm is a good feature—you can de-power without any difficulty, and turning through the wind (tacking) is easier. Of course, you don’t want the CE to be too far aft of the CLR, or you’ll burn out your arm muscles trying to fight the rudder to maintain a heading.

(There’s quite a bit more to this subject than I have indicated here. Two useful books that discuss this balancing act in greater depth are the classic Oceanography and Seamanship by William G. Van Dorn and the very approachable and practical Annapolis Book of Seamanship by John Rousmaniere.)

Some hard-core race boats actually allow the centerboard to be tuned, tilting fore and aft and in some cases even angled relative to centerline, trying to extract that extra 1/10 knot of boat speed. I’m not that devoted to performance; I just want it to work reasonably well in a variety of conditions (and not break). This was another area where we ended up integrating the advice of a lot of marine architects, taking measurements, doing calculations, and constructing an intuition that eventually allowed us to switch from pencils to Sharpies—then fire up the jigsaw to rip a long ugly hole in the beautiful Kevlar hull. The scary thing about all this is that there was essentially no way to test it until a huge amount of additional work was done and the stakes had become significant.

Fortunately, it came out just about right, although in a heavy wind there’s a bit more weather helm (tendency to head up) than I would like—and while researching a book about this, I figured out why. It is conventional wisdom among yacht designers to place the CE slightly forward of the CLR in steady state conditions… knowing that the effective CE will move aft when the boat heels. I figured that since “multihulls sail flat,” I didn’t need to take this compensatory step, and being wary of the dangers of lee helm I established the static CE/CLR relationship the way I wanted it to be under dynamic conditions. But in practice, it turns out that the phenomenon of the CE moving aft is due to mast turbulence and sail inefficiencies, and those affect a multihull just as they do a monohull. The net effect is more arm strain holding the boat off the wind when conditions are intense.

That does beat the alternative, however, and it is somewhat tweakable by adjusting a few variables (deploying a thruster, dropping the dodger, furling the sail slightly, or partially retracting the board).

OK, I think we’ve pretty well completed our brief tour of the center hull. Let’s take a quick look at the crossbeams and outer hulls!

Akas and Amas

As I mentioned, we managed to save a huge amount of work by starting with an existing assembly of crossbeams and outer hulls made for the Fulmar-19 trimaran. This was familiar territory, as I had owned one in the early years of the project—all we had to do was make the Microship hull design backward-compatible with legacy components.

Notice in this photo that the outer hulls kiss the water rather lightly—this was intended, and it was a great relief to see that we got the dihedral about right. Actually, she sits quite a bit lower in the water once stuffed full of heavy touring gear and geek necessities, so the self-congratulation was premature. The goal is to achieve a balance: the less ama immersion, the less hydrodynamic drag from wetted surface, but if one hull is always “flying” to maximize speed, then at rest the boat will rock back and forth in a most annoying fashion. Racers err on the side of speed and fly a hull every chance they get, but my objectives are more sedate.

Another thing to notice is the curve of the akas (the crossbeams), keeping them as high above the water as possible to minimize interaction with waves. These pretty shapes don’t lend themselves to solar panel mounting very well, but it turns out that it’s a moot point anyway—there is so much flexion in the system (a good thing) that the solar array has to move independently of the outer hulls. One of the essential features of this assembly, given the complexity of those landing gear that allow haulouts and portages, is the ability to fold. In the original Fulmar, this was strictly for trailering; nobody in their right mind adds retractable, hydraulically steered full-suspension landing gear to a canoe! But as we had to do exactly that, the folding feature was doubly interesting, reducing the boat to 6-foot overall width (from the original 11) when on the road.

This photo shows how it works. The aka is split in the middle, with a robust pair of anodized aluminum bars forming a simple hinge that pivots around the bolt on the far left. When in use on the water, a stainless steel locking pin is inserted into the empty hole, passing through both of the bars and a couple of nylon bushings set into the flanges of the aka U-section. In practice, this isn’t the most elegant system in the world, however: however tight the assembly feels when assembling the rig prior to launch, there is still a tiny bit of slop that allow the aka segments to work against each other in rough conditions… which is why the photo shows bits of teflon tape to eliminate occasional creaks.

The outer hulls (amas) are simple affairs, with a single screw-on access hatch for inspection. I am often asked if I stow gear out there, but no—I want all the buoyancy I can get and they’d be a pain to reach on the water anyway. As the loads are smoothly distributed, the fiberglass layup is light and simple, interfaced to the akas by simple retaining bolts and molded nests (under normal sailing conditions, there is no focused bending moment here as there is at the junction between akas and center hull).

This photo shows the substantial additional surface that we glassed onto the original amas to allow better footing. Those turned out to be a lifesaver when making the journey between cockpit and dock, over and over, loaded with packs. In a somewhat related vein, being tied alongside a dock (as in a marina slip) subjects the system to additional abuse. People normally use inflatable fenders to reduce noise and abrasion, but the shape of these tiny hulls makes that ineffective—they float up, move around, and otherwise do all they can to avoid being useful. If you look closely at the photo, you can see part of the solution: a black rubber extrusion made to cushion tractor-trailer rigs backing up to loading docks.

On the Road

That pretty well completes the basic substrate, though of course there’s quite a bit more that turns it into the Microship! The landing gear are worthy of another whole article of this scale… they were a huge project, but allowed the boat to be launched and retrieved without a tow vehicle. Here she is emerging from a test sail in 2015, and again at the end of the summer of 2013:

And, of course, meandering through the town of Friday Harbor with the amas folded…

And the exquisite little SpinFin pedal drive unit, built by Bob Stuart:

But those additional details, along with hydraulics and rigging, are topics for another article. (I did a photo essay of the electronic systems that were developed in parallel with this, though of course those are pretty much obsolete by now!) One more teaser… this photo shows the enclosed electronic equipment cowling along with the 480-watt solar array….

Where to Now?

I’m writing this in 2016, revising an earlier version I did on 2004 for the Inside Microship book project (never completed), and the boat is sitting quietly in a rented shop space two miles from the marina where I live aboard Datawake . I have planned to crane-launch the Microship from the upper deck, fulfilling my dream of “scaled technomadics,” but I’ve decided that it would just be too complex…. that’s a job for something light, rotomolded, and turn-key.

So it is getting to be time to find a worthy successor to take over the Microship project… whether for an expedition as I had originally planned while building her (across the US via the Missouri River and then around the Great Loop), as a substrate for intensive geekery and data collection, or something I have yet to imagine. This article, and others to follow, are being added to the archives to provide useful background information for anyone contemplating such an undertaking.

I am deliberately not mentioning a price or other arrangements… that will depend entirely on who takes this on, what kind of public exposure it will generate, and how much I need to be involved. I welcome proposals…

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COMMENTS

Polynesian multihull terminology
A typical fishing canoe of Samoa, showing a simple ama for balance.Polynesian multihull terminology, such as "ama", "aka" and "vaka" (or "waka") are multihull terms that have been widely adopted beyond the South Pacific where these terms originated.This Polynesian terminology is in common use in the Americas and the Pacific but is almost unknown in Europe, where the English terms "hull" and ...
Trimaran Kit with Folding Akas
Features: - Fast and stable Kayak for one or two. - Assembled within 25 minutes to a sailing trimaran, no tools needed. - Waterline length as long as hull length. - Main hull bow with narrow V-shape. - Amas (floats) with optional wave piercing bows. - Amas canted 5° inboard for correct orientation when heeled.
Trimaran
A trimaran (or double-outrigger) is a multihull boat that comprises a main hull and two smaller outrigger hulls (or "floats") which are attached to the main hull with lateral beams. ... ama and aka, respectively (although trimarans are not traditionally Polynesian, ...
Folding Multihulls
Complex Aka Hinge Systems. A complex system for folding multihulls, much like a garage door lift linkage, was developed and patented by Ian Farrier for his trailerable trimaran designs. It allows one person to fold or unfold the boat while it's afloat. Before launching, the mast is stepped and secured with lower stays.
Polynesian multihull terminology explained
The term ama and aka have been widely applied to modern trimarans. In modern sailing, the term is sometimes used to refer to the outrigger on double-outrigger canoes (trimarans), or the two sections of a catamaran. However, calling the two sections of a catamaran by the word ama is not technically correct since they are of equal size.
Longer Amas and Increased Beam
However, if you want more power, amas up to 100%L and with buoyancy over 100% of the total weight will offer more power and add more speed potential, as long as the akas and their attachment to the main hull are designed with adequate strength. See this article on Aka design . As noted, I typically advise that the load on the forward aka beam ...
Multihull Capsize Risk Check
Trimarans tend to be more performance oriented than catamarans. In part, this is because it's easier to design a folding trimaran, and as a result Farrier, Corsair, and Dragonfly trimarans had a disproportionate share of the market. ... Ama is the "pontoon" hull at the end of the aka, or "crossbeam", on each side of a trimaran.
The Complete List of Trimarans
The WindRider 17, an exhilarating ride perfect for families or camper sailors, has been known to reach speeds of up to 20mph. This easy day sailor goes from trailer to sailing in under 30 minutes and is sure to fit in perfectly with whatever adventures you have planned. At a glance: Models: WR 16, 17, Tango, Rave V.
Catamaran
The term ama and aka have been widely applied to modern trimarans. Vaka - A proa consists of a vaka, the main canoe-like hull; an ama, the outrigger; and akas, the poles connecting the ama to the vaka. Semantically, the catamaran is a pair of Vaka held together by Aka, whereas the trimaran is a central Vaka, with Ama on each side, attached by Aka.
2022 Sailing Special Buyer's Guide
This is the smallest model in the range: first presented three years ago, this trimaran was designed primarily for day-sailing, it also excels on coastal trips, where its compact size, maneuverability and performance are outstanding. The Tricat 20, with over 50 units already built, naturally reflects the success of its predecessors, including ...
Demountable Trimarans
The akas on the Doubloon are spaced to allow for a full paddle stroke with the boat setup as a trimaran. There are two sections of tubing that span the opening fore and aft between the akas from which the tramp is mounted. ... The aka tubes are aircraft aluminum and will be segmented with the same spring pins and fitted ferrules you see on take ...
Trimaran
Aka - The aka of a multihull sailboat is a member of the framework that connects the hull to the ama (s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans. Ama - The term ama comes from the proa. The vaka is the main hull, the ama is the outrigger, and the aka or iako (Hawaiian) is the support ...
Seaclipper 16
I started getting answers to that question as soon as I stepped aboard a Seaclipper 16 designed by John Marples of Searunner Multihulls and one of nine designs in the Seaclipper series of trimarans. The hull is constructed of 7 sheets of 1/4″ six-ply marine plywood, five sheets of 3/8″ nine-ply, and lumber in commonly available sizes.
Longer Amas and Increased Beam
The boat will likely be a better sea‑boat and also more stable on a straight line but possibly a little harder to turn. The extra beam and increased ama length will likely make the boat drier but all these positive things can encourage a sailor to push the boat faster and the end price for that is a pitchpole, as the higher stability of the ...
Cross beams/aka's for a 6m (20ft) trimaran
It is 5.10 beam . 5.50 m is very wide beam but you have very low buoyancy outriggers. Mine' are Nacra 5.80 hulls. I use 100 mm OD , 3 mm thick aluminium tubes and water stays. With such a wide beam you need waterstays.
Longer Amas and Increased Beam
Overall beam is significantly higher (14ft vs 12ft), so adding to stability and power to drive the boat. B/L ratio is 0.82 compared to 0.67 for the earlier Cross. This increased stability allows more sail. While the W17 Cruising rig is about the same as the Cross 18, the so-called Race Rig has nearly 20% more sail, which is much appreciated in ...
Adapting a Weta trimaran for solo dinghy cruising
Adjust it tightly to the boat´s shape (save the Weta gelcoat with a plastic sheet and adjust the shape by using polyester putty). Add some neoprene, rubber or foam tape on the edge to seal any gap. I put the bulkhead right in front of the chest (not showed in the photos). 6.2 Plastic sheet.
FARRIER FOLDING SYSTEM™
The Farrier system is the most structurally sound trimaran folding system available, with no hinges in the beams or the critical beam to float join, while corrosion prone wires are never used in structurally critical areas. Overall beam can be varied in seconds, by just one person, anywhere. After 33 years of use world wide the Farrier System ...
Corsair Marine Trimarans
NEW TRIMARANS. Folding System. Legendary Ability, Unbeatable Reliability. Folding and unfolding a Corsair trimaran takes only a minute. With just 4 bolts to remove, it is easily managed by one person, and is normally done while afloat. Simply raise (to fold) or press down (to unfold) the inboard end of one cross beam.
Report on Nine Small Folding Trimarans
The Cross 18 was designed by the famous trimaran designer Norman Cross about 30 years ago. Not surprisingly, like many other designs of this multihull pioneer, this design still has merit today. It uses a simple hinge system for the amas, so that they fold up through 180 degrees to lay side-by-side upside-down over the open cockpit.
Building the Microship Trimaran
The Aka Nests. You've seen them already in the photos above. The task here was to take a pair of curvy crossbeams designed for a small commercial trimaran, and somehow graft them onto a canoe. There are no off-the-shelf brackets that do this, and crudely bolting them on without thinking about stress distribution would be asking for premature ...
Mirage Tandem Island
The Hobie Mirage Tandem Island comes standard with a built-in transducer mount and includes through-hull cable plugs. Excludes taxes, any shipping and set up fees. Sailing has never seemed so simple. When the wind blows, the Hobie Mirage Tandem Island flies across the water, powered by an expansive, easily tended mainsail.

Professional BoatBuilder Magazine

Folding Systems

Catamarans and Proas

Take-Apart Aka Systems

Telescoping Aka Systems

Simple Horizontal Hinge Systems

Complex Aka Hinge Systems

Swing-Wing Systems

Folding Multihulls with Flat Swing-Wing Akas

Complex Swing-Wing Systems

Conclusions

Nomenclature

The Crossbeam (Aka) Structure

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