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Everything You Need To Know About Sailboat Heeling

A sailboat will  heel  or  lean over at an angle when you sail in any direction other than almost straight downwind. The wind pressure on the sails will force the vessel to a sideway angle, while the righting moment of the keel’s weight and lateral resistance in the water counteracts this energy. When a sailboat tilts over like this, it is called  heeling .

For a beginner, heeling over can be intimidating and feel unnatural, and I have seen many white faces on their first sailing trip . I certainly remember my heart beating a bit faster during my first sailing experience.

In this article, I’ll explain everything you need to know about sailboat heeling. I’ll xplain why it happens, and how to control and use it to your advantage. We’ll also cover how to adjust your sails and rigging to reduce or increase heeling, and how to deal with different conditions effectively.

Why do sailboats heel over?

To be able to sail at any angle to the wind, a sailboat needs to take advantage of the wind’s force in the sails to make it move forward.

When air hits the sails at the right angle, it generates lift. Some of the energy will force the boat forward, and the rest will try to push the boat sideways through the water. However, the sailboat’s keel prevents lateral movement sideways to a certain degree, and the remaining energy will make the boat move forward at a sideway angle.

The closer to the wind you sail, the more you heel. As you fall off and start pointing away from the wind, the boat’s heeling angle decreases. Eventually, you will reach a point where you are sailing directly downwind, and the keel doesn’t need to work as hard to provide lateral resistance and move the boat forward because the wind is already blowing in the direction you want to go.

What is the optimal heeling angle?

Some boats like catamarans, trimarans, and planing racing monohulls are designed to be sailed primarily upright. Most cruising monohulls, however, are displacement boats and have to heel to go forward when sailing at an angle to the wind.

Most cruising sailboats generally have an optimal heeling angle of 10-20 degrees. When sailing close-hauled , you might have to push it down to 25 degrees to keep your forward motion, but heeling too far will probably make you slower. 10-15 degrees is a good compromise between performance and comfort.

We have a simple method to find the best heeling angle for our particular boat in the conditions we are sailing. When the boat heels over, it will try to turn itself back up by turning into the wind. This is called  weather helm .

To keep the boat straight on course, we compensate for the weather helm by countersteering with the rudder, which also generates more lift up to a certain point. Compensating too much makes the rudder act like a break, which will slow us down.

Keeping the angle of the rudder between 2 and 7 degrees gives you a nice balance between performance and heeling angle. On many cruising boats with a steering wheel, keeping your center mark between ten and two o’clock is an excellent rule of thumb.

How do you control heeling on a sailboat?

There are several ways to control and reduce the heeling angle when sailing, and there are good reasons why we want to.

A typical scenario is when you are sailing with a good balance on the helm at a decent heeling angle. Then, all of a sudden, the wind increases, and the boat starts to heel excessively. As a result, you get more weather helm as the boat tries harder to round up into the wind, and the wheel gets hard to control.

The boat is now overpowered, and you are heeling too much.

Luckily, we have three easy ways to prevent the boat from heeling too much:

• Adjust sail trim
• Adjust course
• Reduce sail area by reefing

Let us take a look at each of our options.

1. Adjust the sails

De-powering the jib or genoa by easing off the sheets or letting out the mainsail traveler is a quick way to regain control over the boat. If you sail on a reach, easing the sheets will turn the sideway force into forwarding force. When eased far enough, you are actively releasing the wind out of the sail, and the sail will start to luff.

When sailing downwind, easing the sheets is the only viable way to de-power the sails quickly, as you might be unable to turn the boat around and back into the wind. If you get too overpowered, you risk broaching, which can be dangerous.

If the wind increase was just temporary gusts, you might want to either actively work on releasing and pulling the sheets, often referred to as “pumping,” or settle for lower performance and slacker sheets. When you sail upwind, this works as a quick way to de-power the sails, but working with the sheets for every gust means you will lose height and not point well.

This article from Savvy Navvy explains broaching very well and has several videos displaying different broaching situations.

2. Adjust the course

Turning the boat into the wind will take power out of the sails and is easy to do when sailing upwind. When we sail close-hauled, we have a trick we can apply to increase our performance.

A powerful ” feathering ” technique is simple to apply and works well when sailing upwind. Instead of easing the sheets in a gust, you keep the sheet tension and steer the boat higher into the wind. As the apparent wind angle moves aft when the strength increases, we use this to our advantage to keep our height by sailing to the angle of our heel instead of the angle of the wind.

I wrote an article about how high a sailboat can point that you might be interested in :  How High Can A Sailboat Point?

Feathering requires an active and focused helmsman, and as soon as the gust stops, you have to fall off again to keep your heeling angle and not lose power in the sails.

Continuing to fall off and bear away while easing off the sheets will also calm the boat down and make it turn more upright. This technique is helpful if you get tired or feel like you are pushing yourself and the boat too hard. Adjusting the course to a downwind point will also reduce the apparent wind speed and can be a good solution if you need a break.

3. Reduce sail area by reefing

When the wind isn’t just gusting but steadily increasing, it is about time to reduce your sail area by reefing. If the boat is heeling more than 20-25 degrees, you have too much canvas exposed, and reefing at this point will make you sail faster, safer, and more comfortably.

It is advisable to reef earlier rather than later as it can be hard to control the boat when it gets overpowered. Pushing limits while sailing is only for experienced people, and any seasoned cruiser agrees that a conservative approach to increasing weather is smart. If you ask yourself, “Should I take a reef?” the answer is always a big yes.

The reef can easily be shaken out if your hunch was wrong or if it was just some gusts or a short squall. Conservative and safe are the magic keywords. Even if you aren’t anywhere near the maximum heeling angle, less sail area can give you a much more comfortable ride with less heel, even if it means sacrificing a little bit of speed.

How far can a sailboat heel before capsizing?

I get this question a lot, especially from those sailing for their first time. When sailing close hauled, we sometimes push the boat to the point where it may seem like we will tip over and capsize. I often see faces going white when the toe rail dips into the water… Luckily, sailboats are designed very cleverly.

The wind can not heel a sailboat over far enough to capsize. Sailing boats are designed to round up into the wind if they are overpowered   and heeling too much.

It is nearly impossible to fight the helm hard enough for the boat to tip over, even if you want to. And if you could, the rudder will eventually lose grip in the water, and the boat will round up until it points upright into the wind with its sails fluttering.

However, you want to be careful when sailing downwind, especially with a spinnaker. As you are sailing off the wind, your apparent wind is lower than your true wind, and sometimes, it can be hard to notice wind increases. Since the boat doesn’t heel over as much as it does upwind, everything might seem fine until you suddenly are overpowered and going too fast.

Getting overpowered can lead you to a broach, which can knock you over in extreme cases, especially if the waves are big. A keelboat will turn itself around again, but you will probably lose your mast and sails, and we want to avoid that!

Monohull sailboats do heel, and they have to in order to generate forward momentum. How far they heel dramatically depends on the boat. They won’t tip all the way over, even if it may seem so, and will usually round themself up into the wind, where you will be left upright with fluttering sails.

Heeling too much is unsuitable for comfort or speed, and finding a good balance of sail area and weather helm will give you the smoothest ride. Be careful, reef early, and don’t push the limits. Sail your boat conservatively until you gain more experience, and remember to enjoy yourself on the water.

If you want to learn more sailing basics, visit my beginner’s guide here.

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Skipper, Electrician and ROV Pilot

Robin is the founder and owner of Sailing Ellidah and has been living on his sailboat since 2019. He is currently on a journey to sail around the world and is passionate about writing his story and helpful content to inspire others who share his interest in sailing.

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What is Angle of Heel on a Sailboat

And, what Angle of Heel on a Sailboat is acceptable?

What is heeling over on a sailboat?

Heeling over or “heeling” on a sailboat is when it leans over.

Why does a sailboat heel over and why doesn’t it tip over?

Remember your tommee tippee cup? It had a rounded bottom and a weight loaded into the rounded bottom. No matter how much water you put in the cup, the weight at the bottom made sure the cup stood upright – and the rounded bottom meant that if you pushed it over, it would stand right back up.

Your finger pushing sideways on the top of the cup is just like the wind acting on the sails. The wind acting on the sails puts pressure on the sails. Pressure over the entire area of the sails creates a force. The greater the area, the greater the force, and the stronger the wind, the stronger the force. The distance the force is collectively acting on the sails is about 1/3 of the way up the sails. This point is called the center-of-pressure. This is like your finger pushing all the wind’s force at that center-of-pressure point. The sailboat, like the tommee tippee cup has no choice but to lean (heel) over.

The propensity for the sailboat to heel over depends on the height (distance) of the center of pressure above the water line. The physics formula for this is force x distance which equals a physics term called “moment” (not like a moment in time). The “moment” can be considered as the same as “torque” or even easier – as the “tipping force” or (heeling force). The greater the distance and force – the bigger the tipping force.

In high wind conditions, you can lower the center of pressure by spilling some of the wind out of the top of the sails by twisting out the sail at the top (done by easing the mainsheet which allows the boom aft to rise – thus creating less tension on the leech of the sail and allowing the top to twist out).

Twisting out the top of the sail has a double effect. There is less sail area presented to the wind at the top. This means a lower center-of-pressure (less height) and less area – giving rise to less tipping moment.

Another way to lower the center of pressure is to reef the sail (partially lower it). This also acts to reduce the area of the sail. Less area and less height of the center-of-pressure reduces the tipping force. Here is an image showing reefing and twisting effect on the tipping moment. The image also discusses how twisting and reefing moves the center-of-pressure forward. This has the added benefit of reducing what is known as weather helm – the boat wants to automatically turn up into the wind.

What stops the sailboat from completely tipping over?

A balance between gravity acting on the weighted keel and the wind force on the sail stops the boat from completely tipping or heeling over. As the boat heels over, the sail area is not upright and so less sail area is presented to the wind. Also as the boat heels over, gravity acting on the weighted keel that is rolling upwards with the heel of the boat creates a force to stand the boat back upright. At some point, both forces meet in agreement and compromise with a defined heeling angle.

Imagine the weighted keel is just like how your Tommee Tippee cup uses gravity to force the boat to stand back upright. Thus it becomes a balance between the boat being pushed over by the force on the sails and the weight of the keel trying to stand it back up.

See this animation below of the balance of forces. CLICK on the green Increase Wind button. You will see how the “righting force” increases as the weighted keel lifts outwards off the centerline. You’ll also see how the tipping force decreases because less sail area is presented face-on to the wind. It means that the righting force from the keel will always overpower the wind force at some angle of heel. This is not to say that sailboats never tip over, they do but only usually in cases of a massive unprepared-for gust (60+ knots), giant wave, or if they lose their keel. Dinghies of course do tip over from the improper balance of the crew.

What is an acceptable heel angle?

The acceptable angle of heel on a sailboat depends on various factors, including the design of the boat, its ballast, the boat’s purpose, and the prevailing conditions. Generally, here are some guidelines:

• Dinghies and Small Boats : Dinghies are designed to be agile and may heel significantly, especially when sailed aggressively. Capsizes can happen but are often a part of dinghy sailing.
• Cruising Sailboats : Most cruising sailboats are designed to be stable and comfortable. They typically perform best at an angle of heel between 10° and 20°. Once a cruising boat heels beyond 20°, its weather helm tends to increase, making it more challenging to steer, and the boat might not sail as efficiently.
• Racing Sailboats : Racers might push their boats harder, and some racing designs can handle more heel. Nevertheless, excessive heel can still decrease speed as more wetted surface (hull in the water) causes increased drag.
• Multihulls (Catamarans and Trimarans) : These vessels are designed to sail relatively flat. Heeling angles over 10° can be a cause for concern on a multihull. When a multihull starts to heel significantly, there’s a risk of capsize, especially if a hull lifts entirely out of the water.
• Keel Design : Boats with full keels tend to be more stable and resist heeling more than those with fin keels or lifting keels. However, once they reach a certain heeling point, full keel boats can be more challenging to bring back upright.
• Seaworthiness : Some boats, especially bluewater cruisers, are designed to be very seaworthy and can handle significant heel angles, even beyond 45°, without capsizing. Still, this doesn’t mean it’s comfortable or efficient to sail them at such angles.

Factors like gusty winds, big waves, and the condition of your sails (e.g., having a full mainsail up in strong winds) can also influence heel.

What to do if you are getting excessive heeling angle:

• Reef Early : Reducing sail area can help to decrease heeling and make the boat easier to control.
• Adjust Sail Trim : Flatten your sails by tightening the outhaul, cunningham, and backstay (if adjustable).
• Change Your Point of Sail : Sailing more downwind can reduce heeling, but be cautious about accidental jibes.
• Ease the Sheets : Letting out the mainsheet or headsail sheet can reduce power in the sails.

Lastly, the best way to understand how much heel is acceptable for your specific boat is to gain experience in various conditions and, if possible, consult with more seasoned sailors or trainers familiar with your type of boat.

This information was drawn from the NauticEd Skipper Course (for large keelboats) and the NauticEd Skipper Small Keelboat Course . Sign up now to learn the knowledge you need to know to effectively skipper a sailboat.

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Sailboat Heeling Explained In Simple Terms (For Beginners)

If you are new to sailing, then there are many sailing-related terminologies that you will need to learn.

One of those terms is ‘heeling.’ In this article, we will explain what sailboat heeling is and how to control your sailboat when it heels over.

Here is What “Heeling” in Sailing Means:

Heeling is the term used for when a sailboat leans over to either side (port or starboard) in the water by the excess force of the wind. Heeling is normal and counterbalanced by the sailboat’s keel or the crew’s weight distribution on a dinghy.

Table of Contents

What Exactly Makes A Sailboat Heel?

All sailboats are designed to heel, but a sailboat heels over when there is too much wind in the sails, forcing the boat to lean over and lose the harnessed wind power to move it forward.

As a boat heels, the wind pressure on the sails decreases because the sails present a smaller area and less resistance to the wind. The further the boat heels (or leans over), the less pressure.

In addition, boats with a keel have lots of ballast, or weight, to keep them upright in all but the strongest of wind or hurricane conditions. All sailboats will heel or lean over in strong winds, sometimes so far that the rail will dip into the water, and waves will wash onto the deck.

Heeling is simply a part of sailing, and many sailors enjoy it, especially when racing.

How Do I Keep My Sailboat From Heeling?

While all sailboats are designed to heel, sailors can use various techniques to reduce the amount of the angle of the heeling.

These techniques include the following:

Feathering Upwind – 

One of the quickest and easiest techniques a skipper can do in a strong gust of wind is to steer the boat a bit more into the direction of where the wind is coming.

This is called feathering upwind. Doing this releases or spills the wind out of the sails and decreases the wind’s pressure on the sails. This will cause the sails to flap and make a lot of noise (called luffing).

Luffing the sails too much can cause damage to the sails, so this technique is a temporary quick fix and not a long-term solution.

Easing the Mainsheet or the Traveler – 

Another quick technique is to change the angle of the mainsail so that it releases more wind and eases the pressure on the sail.

You can do this by letting out the main sheet (easing the mainsheet) or releasing or easing the traveler control sheet. Both methods will change the angle of the mainsail, releasing the wind pressure and causing your boat to sail more upright.

After a strong gust of wind has passed, you will be able to pull in the mainsail again quickly, to carry on sailing on course.

Reefing the Sails – 

Reefing the sails is a technique used to see or feel that the wind is building or getting stronger. Reefing entails making your sail area smaller, which will work differently on different boats depending on the boat’s set-up.

Reefing the headsail or jib will depend on whether the sailboat has a roller furler or hank on sails. If the boat has hank on sails, you will need to change the headsail to a smaller sail or even a storm jib. Today, most sailboats are equipped with a roller furling headsail, making the headsail sail area smaller.

You can ease the headsail sheet and pull on the roller furler out hauler to roll in the sail a couple of times. This is the equivalent of changing to a smaller sail.

Reefing the mainsail is a little more complicated. Mainsails generally have 2 – 3 reefing points which are stitched in when the sails are made.

The mainsail will need to be partially dropped to access these reefing points, but first, you will need to turn the boat to face the oncoming wind to take the pressure off the sail.

Once you have partially dropped the mainsail, you will need to hook in the reefing point at the mast, haul in the corresponding reefing line, and then retain the main halyard, which is the rope that holds up the mainsail.

How Much Should A Sailboat Heel?

Every sailboat is different, so the exact heel angle for each sailboat will differ.

However, the answer is probably somewhere between 15 and 25 degrees for a comfortable ride in real terms. Thirty degrees is considered the maximum heel for a keel sailboat, depending on the boat’s specific build, design, and characteristics.

Multihulls or catamarans need to be sailed at minimal heel angles; otherwise, they risk capsizing.

But practically, there is a much simpler way to know when your boat is heeling over too far. If you have to fight the steering, otherwise known as the helm, you are heeling too far, and you will need to adjust your sails or course concerning the wind.

How Much Heel Is Too Much?

Similarly, how much heel is too much will also depend on the type of sailing you do. Long-distance cruising, where your boat is your home, will typically involve less heeling than a racing monohull rounding the cans.

However, the amount a sailboat should heel is not opinion. All sailboats are designed to sail at a specified angle of heel. Each sailboat design is for a specific purpose, whether racing, cruising, or somewhere in between, and at their optimum heel angle, there is a minimum wet surface on the boat.

The sails are at a maximum exposure to the wind. When you are sailing and are not at the desired angle, the sailboat is not performing at its full potential.

In addition, if your boat is heeling too much, the boat will become difficult to steer and will slow down. So it’s better to make the necessary adjustments to make yourself and your crew more comfortable and go that little bit faster!

How Far Can A Sailboat Heel Before Capsizing?

For the sake of this article, when we refer to sailboats, we are referring to sailboats with keels and heeling.

Unlike small sailing dinghies, sailboats are designed to heel over without capsizing.

A sailboat is designed to comfortably heel at a certain angle, usually between 15 – 25 degrees. Heeling over more than this is uncomfortable and slows the boat down.

Generally, sailboats with keels can not tip over or capsize under normal sailing conditions. This is because of the weight in the keel. The weight of the keel has been designed to counterbalance the force of the wind in the sails. Plus, the more a boat heels over, the less pressure there is in the sails, and the keel will bring the boat to face into the wind where there is less pressure on the boat overall.

However, this does not mean a sailboat cannot capsize. There are stories of sailboats being knocked down in big waves and strong winds, but this is often temporary as the sailboat will often self-right or come upright by itself.

Extreme conditions such as gale-force winds combined with big seas, too much sail out, and waves crashing over the boat and flooding the cockpit may all combine to capsize a sailboat.

Learning to Sail: Heeling Over

How To Reef A Sail – A Beginners Guide

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Optimal Angle of Heeling

By andrew lesslie.

Have you noticed how some sailors stretch out ahead upwind, while others fall back?

Part of making good progress upwind is keeping the boat to an optimal angle of heel. Too little and you give up power, too much and you might feel fast, but are losing height.

The Merit 25 is wide at the waterline, but has little flare from the waterline to the sheerline. If the boat is heeled too far, the buoyancy concentrated close to the waterline lifts the keel and rudder to the surface very easily.

Take a look at the shot below and note the white water exiting from just astern of the keel. This is indicative of an abrupt and uncontrolled release of pressure from behind the keel, showing that at this, excessive heel angle the boat is unable to convert the drive from the sails to forward motion.

So what does that look like from astern? Here we can clearly see that the underside of the boat on the windward side is entirely out of the water.     Note also the pressure wave that flowing from the rudder, indicating that the boat is sliding sideways and making leeway rather than driving to windward.

In their defense, this boat is lightly crewed and is cruising, they’re dealing with gusts by feathering up into the wind rather than actively trimming.   Note also the loose mainsail luff and very full sails.  Neither is conducive to upwind performance.

So what should you be aiming for? A good heel angle for the Merit 25 is 15° – 20°, less than you would heel a J/24. 

When you find your heel angle exceeding this, move crew weight to windward, flatten the sails and keep the main sheet out of the cleat so your trimmer can ease in  the puffs and sheet back in during the lulls.

In gusty conditions, the benefits from active mainsheet trimming typically exceed the benefits of the extra crew member on the rail.    

The bonus of having another crew member in the cockpit is that they can watch the compass while teh skipper concentrates on driving and can glance regularly under the jib for boats and obstacles.

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Sailboat Stability Uncensored

The merits and limitations of the calculated gz curve..

At its most basic level, my goal as a sailor is pretty simple: keep my neck above water. Speed, comfort, progress toward a destination are nice, but if I need gills to achieve any of these, something is amiss. And since an upside-down boat tends to interfere with this modest ambition, I’d say our recent obsession with stability is justified.

This is far from our first foray into this topic. Shortly after the 1979 Fastnet race disaster , in which 15 sailors died, Practical Sailor embarked on a series of articles on sailboat stability. The racing rules of that era had resulted in designs that were quicker to capsize than their heavier, more conservatively proportioned predecessors, and we needed to explore why.

Since then, the lessons of Fastnet have been absorbed by the design community, culminating with the CE Category system and formulas used by various racing bodies like the Offshore Racing Congress to evaluate a boat’s fitness for the body of water where it will sail. But it’s clear that the tools we use to measure stability, and the standards we’ve established to prevent future incidents are still imperfect instruments, as we saw in the fatal WingNuts capsize in 2011 . And in the cruising community, where fully equipped ocean going boats hardly resemble the lightly loaded models used to calculate stability ratings, we worry that the picture of stability is again becoming blurred by design trends. This video gives some insight into the dockside measurement process for racing boats.

Last month, we examined multihull stability , including an analysis of several well publicized capsizes. One of the key takeaways from that report was the significant impact that hull shape and design can have on a multihull’s ability to stay upright. Another key observation was the distinction between trimarans and cats, and why lumping them together in a discussion of stability can lead to wrong conclusions. As we pointed out, many of the factors that determine a multihull’s ability are related to hull features—like wave-piercing bows—that are difficult to account for when we try to calculate stability.

This month, we take another look at monohull stability. This time it’s a formula-heavy attempt to tackle the conundrum that many cruising sailors face: How can I know if the recorded stability rating for my boat reflects the reality of my own boat? Or, if there is no stability rating from any of the databases, like the one at US Sailing, how do I assess my boat’s stability?

Stability Resources

If you are unfamiliar with this topic, I’d recommend reading three of our previous reports before digging into this month’s article. “ Dissecting the Art of Staying Upright ” and “ Breaking Down Performance ,” both by PS editor-at-large and safety expert Ralph Naranjo, take a broad view of sailboat design elements and how they applies to contemporary sailors. Nick Nicholson an America’s Cup admeasurer and former PS Editor, also offers a succinct discussion of stability in his article, “ In Search of Stability ,” which I recently resurrected from the archives. (Nick, by the way, is no relation to the current editor.)

When we’re talking about stability, the essential bit of information that every sailor should be familiar with is the GZ curve. This graphic illustration of stability highlights the boat’s maximum righting arm, the angle of heel at which resistance to capsize is greatest. It also illustrates the angle of vanishing stability (also called the limit of positive stability), the point at which the boat is just as likely to turn turtle as it is to return upright. Most boats built after 1998 have a GZ curve on file somewhere, and US Sailing keeps a database of hundreds of boats for members. As this month’s article points out, however, the published GZ curve does not always perfectly transfer to our own boats. Nevertheless, it is usually a good benchmark for assessing your boat’s stability ratio—not to be confused with capsize ratio the stability index or STIX .

For a succinct discussion of stability ratios (see below), Ocean Navigator’s excerpt from Nigel Calder’s Cruising Handbook lays good groundwork for the theory. If you really want to dive into the topic, Charlie Doane presents a good overview in this excerpt from his excellent book “ Modern Cruising Design .” Doane, like many marine journalists, relies greatly on the work of Dave Gerr , former director of the Westlawn Institute of Yacht Design and now a professor with SUNY Maritime Institute. Gerr’s four books “ Propeller Handbook ,” “ The Nature of Boats ,” “The Elements of Boat Strength,” and “Boat Mechanical Systems Handbook,” all published by McGraw Hill, illustrate Gerr’s rare talent for taking complicated topics and making them comprehensible and fun to read.

The GZ Curve

Shaped like an “S” on it’s side, the GZ curve illustrates righting lever. The high peak represents a boat’s maximum righting arm (maxRA), the point at which the forces keeping the boat upright (ballast, buoyancy) are strongest. The lowest valley, which dips into negative territory, represents the minimum righting arm (minRA), the point at which these forces are weakest. The curve also clearly delineates the limit of positive stability (LPS, also called the angle of vanishing stability), where the curve crosses into negative territory. Generally speaking, an offshore sailboat should have an LPS of 120 degrees or more. As Naranjo puts it, “It is this ability to recover from a deep capsize that’s like money in the bank to every offshore passagemaker.”

• Notice how lowering ballast lowers the center of gravity (CG) and increases a vessel’s limit of positive stability. In these examples, three identical 30 footers with the same amount of ballast, but differing keel stub depths, alter their draft and GZ curves. Boat 1 (5’ draft), Boat 2 (6’ draft) and Boat 3 (4’ draft). Note that Boat 3, the shoal draft option, has the lowest LPS and Boat 2, has the deepest draft, highest LPS and will sail to windward better than the other two boats. Editor’s note: One would think that with all the reporting we’ve done on stability, we’d be able to label a GZ curve correctly, but in the print version of the March 2021 issue we have mislabeled the curve. I apologize for the error. Sometimes, despite our best efforts, our own GZ curve turns turtle during deadline week. The correct version of the curve appears in the online issue and in the downloadable PDF. If you have questions or comments on boat stability, please feel free to contact me by email a [email protected], or feel free to comment below.

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17 comments.

Thanks for this reminder, another error has crept into the diagrams I think. The yacht seems to have 2 CBs and no GG.

I noticed that also, Halam. With no center of gravity and all buoyancy that boat will never sink. Of course, it could be at rest upside down also.

The link to the US Sailing database is pointing to a different place than I think you intended. It is not the database of boats, but rather information on curve calculation and definitions.

Hi Darrell, sorry to be the bearer of a correction, but it looks like the CG is labeled as CB in the first graphic.

As far as I know, a rule of thumb is that a sail boat can tolerate cross breaking waves not higher than her max beam. Is it true?

It often amuses me to see the many crew sitting out on the gunwale of a keel boat, (monohull) as the righting effect must shorely be minimal. Especially when compared to a small racing trimaran. It does help the ‘Gyration’ as shown in the Fastnet tragedy. Even the ‘Skiffs’ have ‘racks’ out the side, & I’ve seen all sorts of ‘keel arrangements’. They just haven’t put ‘floats’ on the end yet. I’d love to see someone do a ‘stability kidney’, as Lock Crowther said (all those years ago), the the righting, (capsizing force is 35? degrees off the bow. Thought provoking? not antaganistic. Keep up the good work, and thanks ‘B J’.

A useful view of stability is to consider where the energy to resist capsize is stored. As a boat rolls, the center of gravity is also raised with respect to the center of buoyancy, so the weight of the boat is lifted, at least through some angle (as long as the GZ is positive) and energy is stored as a lifted weight. This means that a stability incident is exactly equivalent to rolling a ball up a hill; it will always roll back down until it passes over the top of the hill. This is why most commercial and military stability standards use “righting energy” for at least one criteria. The ISO 12217-1 standard for coastwise and oceangoing power boats requires at least a minimum absolute energy and an energy ratio exceeding a nominal overturning energy of combined wind and wave (similar to the IMO standards for cargo ships and 46 CFR 28.500 for fishing vessels).

Can anyone comment on the stability of Volvo Ocean Race boats? While various mishaps have occurred over the years, I don’t believe any of them have capsized and remained inverted. VOR boats are nothing like the Pacific Seacraft and similar designs from more than 50 years ago, yet they seem “safe”.

Does anyone know why? Size, keel depth and weight, modern design tools?

Good and useful article, particularly to someone considering buying a new or used sailboat. As an add-on to the effect of draft, I would add that most, if not all, builders increase the weight of the keel to try to compensate for the reduction of righting moment with the reduction in draft. I recommend to readers Roger Marshall’s outstanding book entitled “The Complete Guide to Choosing a Cruising Sailboat”. Chapter 3 “Seaworthiness” and chapter 10 “Putting it All Together” are worth the cost of the book many times over. Unfortunately the book is getting out of date, it was published in 1999 and many newer sailboats have come on the market.

Mark, thank you for recommending to read Roger Marshall’s book.

May i suggest reading the book, “Seaworthiness the forgotten Factor”. The author (C.J.Marchaj) makes a number of interesting observations about modern boat design (published in ’86, so not that modern). What sticks with me is the notion that one aspect of seaworthiness is how well a person can survive inside the boat in question– deeper keels make for more righting moment but also a snappy roll, for example, promoting incapacitating seasickness. The boat has to be well enough behaved to “look after” the crew.

My boat 40 ft Samson SeaFarer ketch is fairly tender initially but then settles down once the rail is int he water….but I have never had the top of the mast in the water to see if it would recover well. Since I am not and engineer or math whiz (and don’t want to be!) I wonder if there is a practical way to actually test the stability while on the water. Is there a way for example to pull the top of the mast down to varying degrees/angles and measure the force it takes to do it and use that as a guide to stability. Could that provide some extrapolative certainty to going further around the wheel of misfortune? Crossing between NZ and Australia (45 years ago..) we were knocked over (not my current boat) with the top third of the mast in the water and she righted very quickly (very comforting) – no great mishap except to make the cook go wash the soup out of his hair and confirm all the things we hadn’t tied down…including dishevelled crew.

Cheers Gerry

Can someone please link to the article referenced above on multihull stability? I’ve searched, but cannot find it. Thank you kindly!

I have the same inquiry as Jet. I can’t find the Multihull article. Please advise ASAP!

The link in the 4th paragraph works for me:

https://www.practical-sailor.com/sailboat-reviews/multihull-capsize-risk-check

Couldn’t find this link either. Thanks.

Is it possible to get a link to the USSailing boat database, or some hints on where to find it on the site? The current link just goes to ussailing.org.

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How Heel Affects Speed and Handling

• By Steve Killing And Doug Hunter
• Updated: September 27, 2017

The underwater hull shape of your boat when it heels affects how much sailing length is put to work, how easy it is to steer, and how much horsepower it can carry aloft as the breeze increases. Consequently, some hull shapes must be sailed differently to get the best performance. To explain this concept, let’s compare three of my designs that represent common, but very different, hull shapes: a beamy IOR 40 called Chariot , the long and narrow Canadian 12-Meter True North I with pronounced overhangs, and a 50-foot deep-draft sportboat design, the Daniells 50.

Effective waterline length

A general design rule is that the longer the waterline, the higher the hull’s speed potential. Perhaps the most important change when a boat is heeled is the length of the hull in the water, which is also known as effective waterline length or sailing length. Before the advent of rating rules based on computer performance prediction, designers working with point-measurement rules naturally strove to create hulls with more effective waterline length when heeled than what was measured for ratings purposes when the boat was upright.

The 12-Meter typified this design strategy. The simplest response to outwitting the waterline measurement process was a boat with generous overhangs at the bow and stern, which would stretch the sailing length when the boat heeled. The International Rule, created in 1906, sought to control excessive overhang by measuring a 12-Meter’s sailing length 7 inches above the load waterline (LWL). But there was just too much speed potential in overhangs for designers not to stretch the bow and stern above this point. When these long, narrow, and heavy designs heel to 25 degrees as shown, the deepest part of the hull remains along the centerline near amidships, but locations closer to the bow and stern shift their immersed volume to one side. When this happens, a significant gain in sailing length is achieved, especially at the stern, and a heeled modern 12 develops a particularly noticeable shift in underwater shape outboard of, and behind, the rudder.

It’s a profoundly different shape than that of the sportboat, which was designed without any point-measurement rule to satisfy. This hull is typical of modern sportboat designs, which are either handicapped through computer performance prediction such as the IMS or race in one-design fleets. A clean underwater shape essentially shifts to leeward as the boat heels. Some gain in waterline length results, but not in the dramatic way of a Meter-class boat. It’s not as important, the way it is with designs with pronounced overhangs, to get the sportboat to lay over just to increase hull speed.

Which brings us to Chariot and the issue of how heeling affects a boat’s performance beyond waterline length. Like the 12-Meter, the IOR design is based on a point measurement system. The International Offshore Rule, which was created in 1972, dominated offshore racing design in the 1970s and 1980s. While IOR competition has been superseded by the IMS and one-design offshore classes, the rule lives on in the hulls of many club-based racing keelboats built in an era when racer/cruiser designs routinely took their cue from SORC and Admiral’s Cup winners.

While Chariot isn’t the most extreme product of the IOR, it does show many typical IOR features: a somewhat triangular transom, deep forefoot, large skeg, and a fair amount of beam–emphasized by a designer because the rule assumed that fatter is slower than skinnier. As an IOR design heels, there’s a tendency to pick up sailing length. But because there’s so much volume gathered amidships, if it heels too far, it can begin to rise up, actually shortening the sailing length. As a result, this hull is far less tolerant of heel angle than less beamy designs.

Asymmetry, drag, and control problems

The narrower hull forms of the 12-Meter and the Daniells 50 also encounter far less form drag. This is the kind of parasitic drag an object experiences as it’s being pushed through a fluid, and the narrower a hull is relative to its length, the lower the form drag will be. Because of this, meter-boat hulls can drive comfortably to windward at high degrees of heel with minimum form drag, stretching their sailing length in the process. It’s an advantage enjoyed by other long, narrow hull forms such as Dragons, IODs, and Etchells.

This brings us to another potential consequence of heel. Look at the shapes of the waterline planes in the heeled drawings. (It’s important to consider all the waterline planes, and not just the lightest colored one describing the sailing length.) With Chariot , they’re asymmetric, with long curves on the leeward side and near-straight lines to windward. The heeled 12-Meter displays a less extreme amount of asymmetry, while there’s hardly any with the Daniells 50. Asymmetry encourages the boat to turn to windward, which can lead to control problems. Those problems are compounded by the way a boat settles fore and aft as it rolls to one side.

In most cases, heeled hulls have more volume (read buoyancy) at the stern than the bow, which means that, to different degrees, they want to pitch bow down as they lean over. Even a boat as long and heavy as a 12-Meter benefits from moving crew weight aft as it heels, to counteract the tendency. The effect is most pronounced in Chariot , where it also has the most serious consequences because of things going on at either end of the waterline. IOR boats typically have a deep forefoot with a sharp bow knuckle, and if the bow gets a bite on the passing water as the stern lifts when reaching, a broach is in the making. The control problem is exacerbated by the rudder’s position. As with the 12-Meter, the rudder post is positioned at the end of the design waterline, and as the hull heels, more so in the case of the IOR design, the top of the rudder is in danger of becoming airborne if the stern is allowed to rise. It’s now vulnerable to ventilation down its low-pressure side, reducing efficiency and encouraging a total stall, just when the bow knuckle is digging in, and the heeled hull’s asymmetry is encouraging a sharp turn to windward.

The control problem is less of an issue with the 12-Meter, which lacks the sharp bow knuckle and generally has enough displacement to keep the rudder buried. And it’s least likely to crop up with a modern sportboat, whose shape is noticeably less beamy than that of Chariot , with a wider transom, flatter sections aft, no skeg, and a shallow forefoot. The rudder is positioned well forward of the design waterline’s aft end, and even when the hull is heeled 25 degrees, it’s at minimum risk of inducing ventilation. All that beam aft creates more waterline length when heeled, but at the same time the underwater shape remains symmetrical, which helps maintain a comfortable amount of weather helm. As with the other designs, moving crew weight aft when heeled is a good idea.

Target speed and heel angle

In 20 knots of true wind, our three designs have distinctive optimum performance parameters. Chariot has a target speed of 6.7 knots, but as the beamiest design, to get there the heel angle must be limited to 26 degrees, and sails must be reefed to 80 percent and flattened. The Daniells 50 will make 7.9 knots with the same sail management strategy, but its hull form permits a heel angle of 29 degrees. The 12-Meter True North I , the narrowest and heaviest of the lot, requires no reefing, only flattening of the sails, and can carry 30 degrees of heel as 8.3 knots are achieved.

How much heel your boat can actually tolerate can be investigated by some on-water pacing against an identical or similar design. If you don’t have one already, install a heel gauge and pay attention to it as you draw your observations. An excellent resource to gather hard numbers on how your boat should be handled is US SAILING, which offers valuable performance packages on about 1,500 designs.

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How to measure your yacht’s stability

• julianwolfram
• July 27, 2020

Naval architect Julian Wolfram uses some able hands, scales and maths to explain a practical way to calculate your boat's stability

Measuring, and then adjusting your yacht's stability can affect when you need to reef

Have you ever measured your yacht’s stability?

Adding heavy cruising gear will change your boat’s stability, so it is worth checking, although the names and terms, such as ‘Dellenbaugh angle’ and ‘metacentric height’, might be initially off-putting and leave you flummoxed.

These measures of a yacht’s stability or stiffness – used to compare one boat to another, or modifications that might have done on board – are more reliable than the crude and common ballast/displacement ratio, and understanding them will reveal the impact on your boat of all the additional cruising gear that has been added.

A simple spirit level can be used to conduct your stability experiment. Credit: Graham Snook

Ballast ratio is a flawed because it takes no account of the shape or depth of the keel, or of how heavily loaded the boat is.

Rather than ballast ratio, a better way to assess the stiffness is by dividing the position of her centre of gravity, as measured from the bottom of her keel (known as KG), by her draught, as this takes into account her both her draught and the centroid of ballast on board.

For any yacht built after 2002 the designer or builder will have calculated and potentially measured the KG for the minimum operating condition and probably for the fully loaded condition too.

You will need to induce at least 3° if heel for this to work. Credit: Graham Snook

This data is needed to do the required Recreational Craft Directive (RCD) calculations.

It may also be available for many yachts from before then if the builder or designer was conscientious.

Interestingly, this information has to be provided, by law, for a commercial vessel in the form of a stability booklet and there is no logical reason why it should be withheld from a yacht owner – but that doesn’t mean you’ll get it.

If you want to compare the stiffness of your yachts with others and can’t get hold of the KG, you will have to do an inclining experiment to calculate it.

Strips of wood are used to ensure accuracy. Credit: Graham Snook

An inclining experiment is required for all commercial vessels, including sailing yachts used for commercial purposes, charter and sail training, and is usually carried out, or at least witnessed by, a ship or yacht surveyor.

The inclining experiment yields the metacentric height (GM) which is a primary measure of stability.

Once you have GM then KG can be found using the hydrostatic particulars that are calculated from the table of offsets or the lines plan.

If you can’t get hold of these then you will have to get a 3D laser scan of the boat, when she is out of the water, and a naval architect who has a stability software package to do the calculations for you.

However, doing an inclining experiment is still worthwhile and, on traditional vessels built by eye or for which the lines and hull offsets have long since disappeared, it is the only option for assessing stability.

How to carry out an inclining experiment to check stability

Anyone can carry out an inclining experiment on their own yacht if they wish to check its stability.

It is done afloat, and simply involves moving weight from the centreline towards the deck edge and measuring how much the boat heels as a result.

The weights can be of any sort – jerry-cans full of water, baskets of old chain or the like.

Inclining weight(s) must be large enough to give at least 3° of heel – five large crew should be good for a 12m yacht, the smaller the boat, the fewer people are required. Credit: Graham Snook

I once did an inclining experiment on a 19m ferro-cement schooner with a weight that consisted of a bunch of students weighed on bathroom scales. It worked well.

Traditionally the angle of heel is measured using a pendulum (plumb line attached to a mast) and recording the offset to the side when the vessel heels.

The pendulum is usually damped using a bucket of water or oil.

Nowadays a device known as a stabilograph is often used which is more convenient.

Alternatively, I have used a long (1,830mm) spirit level successfully when the heel angle is between 3 and 6° and I think this is the cheapest and most practical way for a boat owner to give it a go.

Needless to say calm conditions are necessary to get an accurate measurement and mooring lines should be slack so the boat heels in a completely unrestricted manner.

Ideally the experiment should be done in the loaded condition but with the tanks no more than half full.

The crew are ideal inclining weights and six crew will weigh nearly half a ton (and maybe more in some cases!) and they don’t have to be lifted onto and across the boat.

Mark lines each side of and parallel to the centreline close to the deck edges.

Continues below…

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James Jermain looks at the main keel types, their typical performance and the pros and cons of each

The crew will stand facing the same direction with feet together, one foot either side of the line and their weight evenly distributed on both feet.

Ideally there should be one long line marked with chalk or tape on each side of the boat.

That may not be possible, however, and two or more lines may be needed; in which case you will have to note who stands where, as the product of each weight and its distance from the centreline is needed in the calculation.

Start by weighing each of the crew in turn on an accurate set of bathroom scales.

Then put the long spirit level across the cockpit with both ends supported so it is level.

Note the distance between the points of support (x mm).

You should be on the centreline when you are checking the level.

Get the crew on board and along the centreline to start with.

The heel of a yacht has historically been measured using a pendulum. Credit: Richard Langdon

Now get them all to take up positions on one side of the boat and carefully chock up the end of the spirit level so it becomes horizontal.

Pieces of plywood and plastic packers down to 1mm in thickness can be used as you need to measure to the nearest millimetre how much you have chocked up the end of the level (y mm).

Ideally the heel angle will be between 3 and 6° and you will have chocked up the end of the spirit level by at least 100mm.

Take the average of the values as the best estimate of GM. It should be accurate to 1 or 2%.

Typical values of GM range from about 0.8m for a 6m coastal cruiser rising to 1.5m or more for an ocean-going 12m yacht.

Read about what makes a boat seaworthy here

Wide hulls with little freeboard should have higher values; any significantly below this range should give cause for concern.

Knowing GM allows the Dellenbaugh angle, to be estimated.

The heeling arm is the distance between the centre of effort of the sail plan and the centre of lateral resistance of the hull and keel.

These can be estimated from a profile drawing, showing the keel and sail plan and worked out using known measurements.

Once calculated, for a 12m long boat a value of 12° would be considered stiff and 18° tender whereas for a 6m boat 18° would be considered stiff and 26 degrees quite tender.

For those who wish to learn more about this I recommend reading Principles of Yacht Design by Larsson, Eliasson and Orych.

How to measure the stability of your yacht

First you have to wait for Mother Nature to give you a calm day: any wind on the rigging could skew the measurements and drive you mad while you’re trying to get the level correct.

Also consider where you’ll do the test; while it is possible to do this on a mooring, the shelter of a marina is best for accurate results.

You will need to weigh crew to help with your calculations. Credit: Graham Snook

You’ll also need weight: passers-by, friends or relatives will do as long as they can spare you 10 minutes.

If not, jerry cans of spare fuel and water, sails, dinghy and liferaft will be needed.

The bigger the boat, the more weight you’ll need. You’ll also need a spirit level – the longer the better.

If it isn’t long enough to go across the cockpit seats of coaming, use a flat bit of wood long enough to span the gap.

1. Marking and measuring

You need to mark the centreline. Credit: Graham Snook

Marking the centreline on deck, we used masking tape, but a pencil or chalk line would do the trick. Then tape another line parallel to the centreline on deck, remembering to allow room for feet on the outside of the line.

Measure the distance from the centreline to the deck line. Use this measurement (d) to mark a second line on the opposite side. The last measurement you will need is the distance between the supports of your spirit level (x).

2. Prepare the weights

Weights need to be lined up along the centreline. Credit: Graham Snook

Next weigh your helpers or equipment to act as weights – a set of bathroom scales is ideal for this, whether for people or heavy objects. 
Slacken your mooring lines so they don’t affect the way your yacht heels.

Line your weights on the centreline mark and ensure the spirit level is showing your yacht is lying flat in the water. You have to remain on the centreline in the cockpit.

3. The experiment

You need to average the GM figures for both calculations. Credit: Graham Snook

Now move your crew or weights until they are over the deck line; people should stand with one foot either side of the line, weights should be piled up as best as possible. Now pack up the end of the spirit level to bring it level again, then take a note of the thickness of the packing to the nearest millimetre. Repeat the experiment with the weight on the opposite side. Finally, average the GM figures from both calculations.

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M.B. Marsh Design

Understanding monohull sailboat stability curves.

One of the first questions people ask when they discover I mess around with boat designs is: "How do you know it will float?"

Well, making it float is just Archimedes' principle of buoyancy, which we all know about from elementary school: A floating boat displaces water equal to its own weight, and the water pushes upward on the boat with a force equal to its weight. What people usually mean when they ask "How do you know it will float" is really "How do you know it will float upright?"

That's a little bit more complicated, but it's something every skipper and potential boat buyer should understand, at least conceptually. (Warning: High school mathematics is necessary for today's article.)

A yacht at an angle of heel

Let's consider a boat at rest, sitting level in calm water. The boat's mass is centred on a point G, the centre of gravity, and we can think of the force of gravity as acting straight down through this point. The centroid of the boat's underwater volume is called B, the centre of buoyancy. The force of buoyancy is directed straight up through this point.

We now heel the boat over by an angle "phi". Point G doesn't move, but point B does: by heeling the boat, we've lifted her windward side out of the water and immersed her leeward side. The centre of buoyancy, B, therefore shifts to leeward.

The force of buoyancy, acting upward through B, is now offset from the force of gravity, acting downward through G. The perpendicular distance between these two forces, which by convention we call GZ, can be thought of as the length of the lever that the buoyancy force is using to try to bring the boat upright. GZ is the "righting arm".

If we draw a line straight upward from B, it will intersect the ship's centreline at a point called M, known as the "metacentre". (Strictly speaking, the term "metacentre" applies only when phi is very tiny, but a pseudo-metacentre exists at any given angle of heel.) The metacentric height is a useful quantity to know when calculating changes in trim and heel.

(Can't see the images? Click here for now , then go update your web browser.)

We can easily draw a few conclusions simply by looking at the geometry:

• The boat will be harder to heel, i.e. more stable, if GZ is increased.
• Lowering the centre of gravity, G, will increase GZ.
• Moving the heeled centre of buoyancy to leeward will increase GZ.
• If GZ changes direction- i.e. if Z is to the left of G- the lever arm will help to capsize the boat instead of righting it.

Stability Curves: GZ at all angles of heel

To prepare a stability curve, the designer must find GZ for each angle of heel. To do this, she must compute the location of B at each angle of heel, and determine the height of G above the base of the keel (the distance KG).

In the early 20th century, finding B at each angle of heel was an extremely tedious process involving a lot of trial-and-error, a lot of calculus, and days or weeks of an engineer's time. Today, this can be computerized, and takes only a few seconds once the hull is modelled in a CAD program. Finding KG, though, is still a tedious process: it can either be measured by moving weights around on an existing boat and measuring the resulting angle of heel, or it can be calculated by tallying up every piece of structure, ballast, equipment and cargo on the boat.

Once that math is done, the designer can plot GZ (or righting moment, i.e. displacement times GZ) over all possible angles of heel. This produces the familar stability curve:

All yacht skippers should be at least somewhat familiar with their own boat's stability curve, and it's a useful thing to study when buying a boat. To read the curve, we look at the following features:

• The slope of the curve at low angles of heel tells us whether the boat is tender (shallow slope) or stiff (steep slope).
• The righting moment at 15 to 30 degrees of heel tells us about the boat's sail-carrying power. A large righting moment indicates a boat that can fly a lot of sail; a boat with a lower righting moment will need her sails reefed down earlier.
• The maximum righting arm (or righting moment), and the heel angle at that point, tells us where the boat will be fighting her hardest to get back upright. If this is at a low angle of heel, we have a boat with high initial stability- she'll feel very stable under normal conditions, but a bit touchy at her limits, and relies on her skipper's skill to avoid knock-downs. If the maximum righting arm occurs at a very large angle of heel, the designer chose to emphasize ultimate stability- she'll be hard to capsize, but will heel more than you might expect in normal sailing.
• The angle of vanishing stability is the point where the boat says "Meh, I'm done" and stops trying to right herself. Looking at the diagram above, this means that Z is now at the same point as G. A larger AVS indicates a boat that's harder to capsize.
• The region of positive stability is the region in which the boat will try to right herself. The integral of the righting moment curve (i.e. the area of the green region) is an indicator of how much energy is needed to capsize her.
• In the region of negative stability , the boat will give up and roll on her back, her keel pointing skyward. The integral of this region (i.e. the blue area) tells us how much energy it'll take to right her from a capsize; if this area is relatively small, the waves that helped capsize her might have enough energy to bring her back upright.

Try it on a real boat

How does this apply to some real boats? Let's consider a 10 metre, 8 tonne double-ender yacht of fairly typical layout and proportions. The parent hull looks something like this:

Keeping her draught (1.5 m), displacement (8 tonnes), length (10 m), freeboard, deckhouse shape, etc. the same, we'll adjust the shape of the midship section to yield four boats that are directly comparable in all respects except beam and section shape. Hull A is a deep "plank on edge" style , hulls B and C are moderate cruising yacht shapes, and the wide, shallow-bilged hull D resembles an old sandbagger - or a modern racing sloop.

Now, assuming that G lies on the waterline (so KG = 1.5 m), we can compute the righting arm GZ as a function of the heel angle. If we multiply the righting arm GZ by the displacement, we get the righting moment.

Some immediate observations from this graph:

• The narrow hull "A" has relatively little sail-carrying power at low angles of heel, but will self-right from any capsize. Her good "ultimate stability" comes from using ballast to get G as low as possible.
• The wide hull "D" can fly a lot more sail, but if she goes over, she ain't coming back up. She gets her high "initial stability" from her wide beam, which moves the heeled centre of buoyancy farther to leeward.

There's a problem, though: We've assumed an identical centre of gravity for all four boats. That's not realistic. The deep, narrow hull will have her engine and tanks low in the bilge; the wide hull must mount these heavy components higher up. Let's reduce hull A's KG measurement to 1.35 m, and increase hull D's KG measurement to 1.65 m, a more realistic value. We'll scale KG for the other two accordingly.

The overall conclusions don't change much, but we now have some realistic numbers to play with.

• Hull A, the narrow one, will have a hard time flying much sail. She'll heel way over in a breeze. But she can't get stuck upside down.
• Hull B, a moderately slender cruising shape, also can't get stuck upside down- her AVS is 170 degrees. Her extra beam causes the centre of buoyancy to move farther to leeward when she heels, so she has more initial / form stability than hull A and can carry more sail.
• Hull C, which is typical of modern cruising yachts, has over twice the sail-carrying power of the slender hull A. She'll heel less, and since her midship section is much larger, she'll have more space for accommodations. The penalty is an AVS of 130 degrees. That's high enough that she can't be knocked down by wind alone, but wind plus a breaking wave- such as in a broach situation - could leave the boat upside down until a sufficiently large wave comes along.
• Hull D, the broad-beamed flyer, can hoist more than three times the sail of hull A at the same angle of heel. She'll be quite a sight on the race course with all that canvas flying. Her maximum righting moment, though, is only 37% more than hull A's, which leaves less of a margin for error- hull D is more likely to get caught with too much sail up, and will reach zero stability at a lower angle of heel. If she does go over, she has considerable negative stability, making it unlikely that she'll get back upright.

Work to capsize

If you're one of that slim percentage who paid attention in high school physics, you're probably looking at those curves and thinking: "Force (or moment) as a function of distance (or angle).... hey, if you integrate that, you get the work done !

And so you do, with the caveat that we're using a static approximation to a dynamic situation. The results are valid for comparison, but the actual numbers may not mean very much.

Let's do that for each of our hulls. We'll integrate the righting moment curve as a function of heel angle, up to the angle of vanishing stability, to get the work done to capsize the boat. We'll also integrate from the AVS to 180 degrees to get the work done to right the boat from a capsize.

Our four boats require roughly the same work to capsize! Changing the shape of the midsection affected the shape of the stability curve- a wider boat had more initial stability and less ultimate stability. In this case, though, our vessels are all about the same size and require about the same amount of work to capsize.

Righting from a capsize is another matter. The narrow, deep hulls A and B will self-right without any outside influence- a nice confidence-booster if you're heading into the open ocean, although the reduced sail-carrying power and limited interior space of these vessels will probably be more important to most skippers.

The moderate cruising hull, C, needs a bit of help to self-right, but any combination of wind and waves that can do 95 kN.m.rad of work on the boat is likely to produce a wave that can do 10 kN.m.rad of work on that same boat.

Our broad-beamed racer, hull D, is not so fortunate. Righting her from a capsize takes one-third the work that capsizing her in the first place did, and her acres of canvas were probably a major factor in the initial capsize- they're now underwater, damping her roll motion instead of catching the wind. The odds are that this boat will stay upside-down until someone comes along with a tugboat or crane.

Lessons Learned

What's the take-home message from all this?

If you're buying a new boat: Look at her stability curve, and compare it to other boats.

• Good: Large region of positive stability, small region of negative stability, high angle of vanishing stability, steep slope at low heel angles.
• Iffy: Shallow slope at low heel angles (makes it hard to fly lots of sail, excessive heeling when underway).
• Risky: Low angle of vanishing stability, large region of negative stability.

If you already have a boat:

• If you know her point of maximum stability, you can be sure to reef the sails well before  that point.
• If you know her AVS and the shape of the curve in that region, then when a broach or knockdown happens, you already know how hard she'll fight to come back upright.
• If you know how much area is covered by the negative stability region of the curve, you'll have some idea of whether she'll come back from a capsize on her own or else have to wait for help.
• Determine if anything you've changed- a dinghy added on the deck, perhaps- has moved the centre of gravity.
• If G has moved, adjust your mental model of the stability curve accordingly: just shift the curve up or down by (change in height KG) * sin(heel angle).

Confounding Factors

What we've discussed here is just about how to read the stability curve- it's not a complete picture.

There are many other factors that must be considered to get a complete understanding of a boat's stability. Among them:

• Dynamic effects. Everything discussed so far is for the static case, and is good for comparison purposes. But in practice, boats move.
• Waves. Stability curves are calculated for flat water, ignoring the effect of waves.
• Differences in rigging. Weight aloft has a much larger effect on the boat than weight down low- particularly where the roll moment of inertia, an important property for dynamic stability, is concerned.
• Keel shape. Keels tend to damp rolling motion; this behaviour is quite different with a long keel than with a fin keel, or with a fin keel underway versus a fin keel at rest.
• Downflooding. Everything we've discussed here assumes that the boat is watertight in any position. If she takes on water when rolled, everything changes.
• Cockpits. Our demonstration boat doesn't have a cockpit. A large cockpit could hold several tonnes of water- and with a free surface, no less. That means that G will move all over the place, usually in the wrong direction.

Further Reading

Steve Dashew's article " Evaluating Stability and Capsize Risks For Yachts ", and others on his site, discuss stability-related risks as they relate to cruising yachts.

Technically-minded readers should refer to a naval architecture textbook, of which my present favourite is Larsson & Eliasson "Principles of Yacht Design" (McGraw-Hill).

Don't even think about buying a cruising yacht without first reading John Harries' extensive series of articles on boat and gear selection .

Topic: 

• Boat Design

Boats: 

Great stuff.

A really great piece, thank you. You have the very unusual gift of being able to make complex issues easy to understand.

Other confounding factors

One major confounding factor which most English-speaking designers still seem to routinely dismiss, or overlook, is to do with the nature of knockdown lever moments in a 'survival storm' situation:

You specifically state you're not taking waves into account, so this is addressed at those who do, in the conventional way -- generally led by the insights of academics and researchers tracing their conceptual methodology back to the likes of Marchaj.

The lever moments I'm thinking of arise from the vertical offset between: Where the wave force vector acts, and Where the hull resistance vector is located.

It has long been contended by the school of expedition yacht designers, going back to around the days of Damien II, from France in the 70s, that the greatest risk ... and arguably the only one worth worrying about for such vessels ... was due to the tripping moment caused by the vertical offset between the centre of effort of a true breaking wave, and the centre of resistance of the hull AND UNDERWATER APPENDAGES

When a large ocean wave breaks entirely forwards, the part which was formerly the crest avalanches down the front of the wave. Admittedly this behaviour is VERY rare offshore - where almost all 'breakers' actually spill most of the water down the back, but it's these events which present a real survival threat, and which define the limits to a vessel's capability.

Unlike the water particles in the body of the wave, which are circulating in the well known way of text book diagrams, and effectively not going anywhere over time, this "former crest" water has escaped from the wave system and is travelling rapidly under the influence of gravity down a steep ramp whose geometry (as opposed to constituent particles), in the case of a Southern Ocean wave of truly heroic proportions, might itself be advancing as fast as 30 to 40 knots.

So we have an aerated but still rather massive entity tumbling down above this already very fast moving ramp, hitting the topsides and cabin coamings, in the worst case, perpendicularly.

The contention of the French school was that, in this situation, while a high freeboard is clearly undesirable, the absolute last thing you want, which trumps everything else, is deep appendages providing lots of lateral grip, situated down in green water. This would provide a lever arm converting the sideways impulse (which is at a height not very far from the centre of mass, and hence not inherently an insuperable problem) into a very dangerous overturning moment.

The insight was based on simple empirical observations, such as of a flat wooden plank, or a surfboard with no appendages, floating side on to breaking waves at a surf beach. Despite having no ballast whatsoever, and a zero GZ in the plank case, this will sideslip down those waves and stay happily the same way up, in conditions where (say) a windsurf board with a deep centreboard (whether ballasted or not) will be tumbled repeatedly.

They reasoned that the thing to avoid at all costs, for a well found expedition yacht, was a knockdown with an angular acceleration sufficient to snap the rig.

This turned everything on its head with regard to the conventions of stability calculations: the relative positions of the centre of mass and the centre of buoyancy become largely irrelevant: the former should if anything ideally be high, so the vector from the striking crest passes through or near it, (to minimise the inertial overturning moment) while the latter is almost irrelevant because on the face of such a steep wave, the hull is in virtual freefall, and the hull is largely disengaged from green water. Aerated water offers little buoyancy.

This is so divorced from statics (which are arguably most useful for calculating how to prevent ships capsizing at a dock) that it is a shame to see so much reliance on static measures persisting to this day, in educating sailors, defining ultimate seaworthiness, and framing regulations and recommendations.

Be that as it may: this insight led to a completely different school of storm management by the adventurous people who sailed off to places like the subAntarctic and Antarctic in the new generation of beamy, generally low-freeboard # hulls, equipped with swing (or even dagger) ballasted keels capable of retracting - in many cases - right within the canoe body.

# ideally, no cabin trunk - which on the face of it is bad for self-righting...

In survival conditions, these sailors began retracting these keels, even though on the face of static stability calcs, this is entirely wrong. And (AFAIK*) not one of these yachts has yet been lost in the deep south, despite them making up the majority of the fleet, and I'm not even aware of a single 180deg knockdown to such a vessel configured in this way.

There have been, and continue to be, numerous knockdowns and dismastings of fixed-keel yachts designed to the other, older paradigm.

*(The first two losses of private expedition yachts in Antarctic waters both occurred within the last two years, and neither was a vessel of this type)

So even if these sailors are not right, they're clearly not VERY wrong.

Re: Other confounding factors

You are quite correct that when you are facing breaking waves, static stability analysis is not going to show the whole picture. Being caught in large breakers is certainly one of the highest-risk situations a yacht can face.

The "let it slide sideways" approach can have considerable merit in such a situation, if the boat is designed with this in mind. On a monohull sailing vessel, this calls for a retractable keel and a canoe body with relatively little lateral resistance of its own. If you do this, of course, you also have to ensure that the vessel won't trip over the leeward gunwale when she's surfing sideways with the keel retracted. There are plenty of good, seaworthy vessels out there with such a configuration.

The price you pay for doing it that way is that it's harder to right the boat if she does capsize. Frankly, though, I would rather not capsize in a non-self-righting boat than be upside-down in one that will eventually get herself back up. There are tens of thousands of catamaran sailors out there who would seem to agree.

This is not to say that static stability traits are not important: they certainly are. Given two vessels of generally similar configuration, the stability curves will tell you quite a lot about what kind of behaviour can be expected from each.

Static stability curves are certainly not the whole picture. There are several important dynamic aspects- the lateral resistance effects and the roll moment of inertia, among other features- that can have a huge effect in extreme situations. I'll discuss these in more detail in future posts.

I am thinking about. Buying a

I am thinking about. Buying a 38 foot guimond lobster boat. I am thinking Of widening the stern to 10 feet from 8 ft 8 in. Also I want to add some fiberglass to the keel to make her a little deeper maybe 36 in from present 32 inches. Should I make the new hull water line 90 degrees? Will this be better than a round traditional edge? Should I add bilge keel fins for more stability?

Modifying a design

The kind of modifications you're describing are fairly extensive. You would be wise to arrange a meeting with a naval architect, or with a builder who has extensive experience with that type of boat. With the boat's drawings and a good description of what performance characteristics you want, the professional will be able to assess what modifications (if any) would be appropriate- or if you'd be better off choosing a different design from the start.

Stabilty of Twin Keel Monohulls (Bilge Keel)

Wondering about the stability of bilge keeled sailboats, specifically the Snapdragon 26. How does a second keel affect relative stability of this kind of vessel? Any thoughts appreciated.

Static stability is determined by the hull shape and by the distribution of mass, i.e. the centre of gravity. Two identical hulls, one with a single fin and one with twin keels, will have approximately the same stability curve if they have the same centre of gravity. The twin keel configuration is usually chosen to allow shallower draught, though, so the centre of gravity will often be higher than for a single-fin boat.

There is a significant performance sacrifice with this configuration. A higher centre of gravity reduces the sail-carrying ability, the lower aspect ratio foils are not as efficient to windward, and the extra wetted surface increases drag. The flip side is that you can safely dry out at low tide in places where most monohulls would never be able to go.

Ultimately, though, the keel configuration is a fundamental part of a design, and there's no real answer to "How does a second keel affect stability". It's the performance of the entire boat that matters, and unless you have two boats that are identical except for keel configuration, it doesn't make much sense to separate out this one aspect of the design. The class's performance record and the experiences of skippers who have sailed that class in bad weather are better ways to assess the relative seaworthiness of an existing design.

Stability Curves for Hunter 34

I'm french and it's not that easy for me to understand all of this but here is my question:

Do you know who I can contact to know the stability curves of my sailboat. It's a Hunter Sloop 34' 1985

I asked directly at Marlow-Hunter, they said they don't have this information.

Someone told me that Hunter Manufacturer has it and that I can have it for some dollars but it seems that this is not the case.

Can you help me?

Tracking down data for old boats

Danielle, if I'm not mistaken, that Hunter would be one of Cortland Steck's designs. There's a chance that he might have the data you're looking for.

Stability curves are incredibly tedious to calculate without a computer, though, so many- if not most- boats designed prior to the advent of modern 3D CAD never had one calculated at all. It's possible to build a computer model of an existing boat and calculate the required data, but for most practical purposes you can find the important information through an inclining experiment. This essentially consists of moving known weights around the boat and measuring how she heels in various load conditions, and it's one of the more common ways of measuring stability data for an existing vessel in commercial service where all of these details must, by law, be properly measured and documented.

Righting a Capsized Vanguard Nomad 17

I read on the web that it takes 420 lbs of crew weight to right a capsized Nomad. Is that true? I weigh 135 lbs and I sail single-handed. It's now November and the water is getting too cold to find out.

Re: Righting a Capsized Vanguard Nomad 17

Gerardo, A 625 pound boat with a beam of 8 feet is not going to be an easy thing to right. You might find Sailing World's article on the boat interesting. They were advised by the manufacturer's rep that the boat can't be righted by one person in the way that you'd right something small like a Laser. But if you flood the tank (through the spinnaker well) on one side, you'll be able to roll her far enough to pull her back up like a dinghy, and then drain the tank again. I agree that you would NOT want to test this in November!

37 Foot Sailboat

I am from the Maldives in the Indian Ocean. I am building a fiberglass sailing yacht using local boat builders. Its 37 feet and 11 feet with a long keel of 3 foot deep. And will use concrete in the keel. They will be putting 9 fiberglass mats. Interior and the bulkheads will be done using marine plywood. The hull is going to look more like a Fisher 37. And the cabins like a Nauticat. I am intending to use ketch style two masts. I was surfing the internet and am trying to understand what are the issues that I need to take into consideration. Your explanations is very helpful. I am just wondering whether you will comfortable if I communicate on this topic. Thanking you.

Re: 37 Foot Sailboat

Ahmed, it's good to have you here and feel free to chime in on relevant threads, or to contact me directly. It's always neat to see what everyone else is building.

Help with stability estimate

Matt, I found your article very informative, good stuff! Where might you think my vessel Crusoe might fit A thru D.
 57' O.L. 13' beam-25 tons-4.5 ton ballast lifting keel. Here is the vessel:
 
 http://yachthub.com/list/yachts-for-sale/used/sail-monohulls/pilothouse-... 
 thanks,
 
 Thomas

To summarize, in very general terms: Category A is an offshore-capable yacht. Category B is a coastal cruising vessel, able to handle weather at sea but not recommended for extended offshore use. Category C is a short-range inshore vessel that is expected to take shelter rather than facing a storm out in the open. Category D is a small, fair-weather vessel such as a skiff or dinghy. The static stability properties are the main factor that determine which category a particular boat design is intended to fall in. But, in addition, the builder must comply with dozens of requirements for structural integrity, watertightness, emergency equipment, etc. for the boat to actually fall in that category. It's quite possible for a boat designed for Category A to end up being a Category B vessel because of corner-cutting during the build.

Assessing Southerlies and Tayanas

Would you care to give an opinion on the Southerly Yachts with retractible keels and twin rudders, also on Tayanas as to seaworthiness and construction. Thank you

Southerly & Tayana

I don't have first-hand experience with either of these marques, so I'm afraid I can't offer much that's meaningful.

Southerly tends to have a fairly good reputation. You do pay a fairly substantial premium for the complicated retracting keel, but there are some cruising grounds where the only options are a retractable keel or a multihull.

The Tayana line has produced a mix of models from several different designers, some very traditional, rugged and slow, others relatively modern. I'd have to know exactly which one you have in mind to say much more than that.

Your best bet for meaningful data on either line would be to prowl some forums looking for the owner's club for each marque. Yacht owners generally love to talk about their yachts, and if you're patient, you can usually find most or all of a particular model's weak spots by asking owners how they handle rough weather and what they've had to fix or replace so far.

I really enjoyed your article

I really enjoyed your article. I'm trying to make a stability model myself and I was interesting in the equations you used to find GZ as a function of heel angle and then how you found the displacement. I'm also interested in how you calculated the different curves for the different hull designs. Any pointers would be greatly appreciated. Thanks!

I'm not sure if I mentioned

I'm not sure if I mentioned it in my last comment, but I'd also like the equations for getting the displacement you multiplied GZ by. Thanks!

Sources for calculations

Hi Cole, Finding the displacement from the lines is pretty easy. If it's a CAD model, just find the volume; if it's a 2D drawing, find the area of each of the stations and use Simpson's rule to integrate over the waterline length. Finding G is just a matter of adding up the weights and moments for every component of the ship - each frame, the hull planking, the engine, each piece of hardware, and so on. Finding GZ for a given heel angle is relatively tedious, but it's essentially the same procedure (find the station areas, integrate over the waterline length, find the station centroids, weight the centroid offsets by station area to find the CB). There is an iterative step here as you must adjust the waterline position to make the displacement the same as in the at-rest case. For practical purposes, though, virtually everyone computes their stability curves using a proven software tool like Orca3D or ArchimedesMB. The actual calculations are described in detail in most good yacht design textbooks, eg. Larsson & Eliasson's "Principles of Yacht Design".

Stability of Chinese Junk Hull

Hi Matt, Your article is very informative. I am studying the feasibility of building a wooden ocean going Chinese Junk. History recorded that there were huge junks sailing 600 years ago in Zhenghe's days. The latest record for a large junk sailing across oceans is the Keying which sailed from Hong Kong to New York and London in 1848. She is 160ft LOA, 33ft BEAM and 13ft (rudder up) 23ft (rudder down) DRAFT, 700-800 ton DISPLACEMENT. As it is too difficult to re-build a wooden junk of such size, I am studying the record of fishing junks built about 30 years ago. A junk capable of sailing in force 8 wind. She is 23m(75.4ft)LOA, 5.66m BEAM, 1.69m(DRAFT), 1.2m(FREEBOARD), 138000kg (DISPLACEMENT). There is a dagger board extending 2.5m from the bottom, located about 1/3 waterline from the bow in front of the main mast. The rudder can be raised in shallow water. It is perforated with an area of 6.7sq.meter. The bottom is almost flat. The design of junks were evolved from generations of experience without scientific verification. I am surprised that the length and beam is so close to Volvo 65, but the displacement is 10 times those of Volvo. I am wondering if a flat bottomed boat is stable in rough ocean condition until I read the comment by Andrew Troup in 2012 about a boat without appendages can surf safely on the steep slope of the waves. I am glad if you can shine some light on the stability of traditional Chinese junks. John Kwong

Chinese Junk

A hundred and thirty-eight tonnes on 23m LOA? Yowzah, that's quite the boat. There's nothing fundamentally wrong with a relatively flat bottomed shape, or with retractable appendages. The risk of a flat bottom is more to do with slamming and pounding, which is much less of a problem in a heavy boat. Before investing hundreds of thousands of dollars in such a boat today, it would certainly be prudent to have the design drawn up and analyzed with modern software tools. There are certainly improvements from the last 50 years that could be applied to a much older design. A six-century pedigree is nothing to sneer at, though, and the fundamental design - updated with some modern construction techniques and with the added confidence of a full stability analysis - might still be a good one.

Relative locations of G and B

Hi Matthew. Thanks for such an interesting and informative article. Most diagrams show B below G so I guess this must be the most usual arrangement. However, I wondered if there might be a class of yacht (lightweight but with deep bulb keel) where G moved below B. I guess this would give a very good static G-Z curve (but I note also the comments made by Andrew (above) re dynamic stability that this might not be the best design to go winter sailing in the Southern Ocean!)

Monocat Hull

Matt what would you think this Monocat 50 Hull Form (see link)? Its a very different design- Monohull at the Bow, Catamaran at the Stern, 2x Lift Keels, One Ballasted, the other Forward non ballasted dagger board. I just cannot find information on it anywhere? I'd assume it would have similar characteristics to a very beamy monohull and thus would not self-right from a knockdown!? This is what im wanting to find out, will it self-right & is it safe offshore? Mashford Monocat 50 15.24m LOA 5m Beam 3Ton Ballested Lift Keel 0.8m - 2.1m

(there is a cad drawing of its underwater hull design in this advert) NB: Unfortunately your Spam Filter will not let me paste the link, but if you search the internet for MASHFORD MONOCAT it comes up for sale everywhere.

Ive been trying to locate the Designer Chris Mashford with no luck? feel free to email me too any info, cheers. Mal

Mashford Monocat

I'm not too familiar with the Monocat. My educated guess would be that stability-wise, it'll be much like a "skimming dish" racer - very stiff and powerful at first, hairy at the edge, and not self-righting. I'd have to sail one to be sure, but I have a suspicion that it could have the worst of both worlds - the relatively high drag and the ballast burden of a mono, with the complexity and high sailing loads of a cat. The main appeal seems to be the huge living space in a relatively modest beam, suggesting it's meant for short-term coastal cruises and charter work. Reliable reports on them seem to be very hard to come by, I suspect they weren't built in large numbers.

Great article! Thanks. My question is on actual statistics of vessels that have actually capsized. Understanding that this would likely be under reported, it would seem fruitful ground to examine questions of which static or dynamic factors pan out and are predictive for hulls that ended up upside down, and the stories behind them?

Does such a database exist?

reason for knowing the departure gm

Sorry I am bringing in a different topic entirely . pls I have read most of your articles and I have found them to be very useful . Pls I really want to know the importance of knowing your departure gm before commencing on a voyage... thank you

downflooding

Hi Matthew - I was reading your blog just now on Aug 23. I wanted to know how intake of 450l water affected the stability of a 9000kg / 41ft sailing yacht that I was skippering in a force 9 storm around Dover on Aug 3rd 2017. We encountered rather high waves of estimated 7m and had 52 kts apparent wind, which may have been the beginning of a force 10, because we did only 4kts through the water under storm jib and 3x reefed main. Once safely parked in Dover, we pumped 450l water out of the boat. Floorboards were floating... Any idea how that amount of water may have affected stability?

Kind regards

Martin Lossie

Calculating a stability curve

You mentioned calculating stability curves is tedious, and mostly done with CAD these days. I'm a new owner of a 1969 Columbia 26 Mk II and would love to understand the stability curve for my boat. A few enterprising owners have rescued the blueprints of this boat and placed them online, so I have the measurements available. Are there folks out there willing to do the CAD work to create the curve? Otherwise, what would be the easiest way for me to get one created for my boat?

Thanks for a GREAT article explaining this concept!

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• Yachting World
• Digital Edition

Sailing instrument calibration: How to set up your yacht for accurate readings

• July 20, 2020

A yacht’s instrument system can only be as good as the care with which it was set-up; ‘garbage in, garbage out’ is as true of a boat’s computer as any other, writes Mark Chisnell

Choose flat water and a quiet time of day for instrument calibration as you need to maintain consistent speeds and rate of turn under engine. Photo: Paul Wyeth

These tweaks will help make any integrated instrument system accurate and effective, whether the goal is to win races, or cruise efficiently, comfortably and safely.

The real key to setting up any instrument is careful calibration. I hate to say it, but this is one of the times when it’s worth reading the manual. It’s particularly important to approach sailing instrument calibration in a systematic order.

A lot of the data is interdependent, with much of the most useful information derived from the measurement of only five values: boat speed; compass heading; heel angle; apparent wind speed; and apparent wind angle.

It’s vital to calibrate these sensors first, and only when they are done accurately move onto whatever calibrations are provided for other functions like true wind speed and direction.

Compass set up and calibration

Electronic compasses will have the exact details of the best calibration routine described in their manuals, but it usually involves turning the boat in a circle or two. This allows the compass to calculate its own deviation curve and compensate for the local magnetic environment.

For example, to set up a Simrad Precision-9 compass requires the yacht to complete a 390° turn with a steady turn rate of 2°-3° per second. Once the turns are completed the compass applies the new deviation adjustment and sends a message that it’s finished.

There are a few things to watch out for in this process. It’s a lot easier and more accurate in flat, open water with no wind and no current because the turns need to be steady and even – so it won’t work if the yacht has to adjust course to avoid hitting something during the calibration.

Article continues below…

How new-age sailing autopilot systems are putting computers at the helm

A couple of decades ago I’d have recommended anyone planning an ocean crossing without a big crew to fit wind…

Can augmented reality really give us a vision of the future of sailing?

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Check beforehand that there is no magnetic material anywhere near the compass sensor, with everything stowed in its normal sailing position. Beware of mobile phones in pockets of people sitting on deck, often right above the compass fitted below.

Once compass calibration is done, check the physical alignment of the instrument relative to the centreline of the boat by sailing down a known transit line. I also always check the boat compass against any hand bearing compasses on board – it’s useful to know if they disagree, because then a deviation card can be created for the difference.

Boat speed calibration should be one of the first jobs completed on any new boat, or at the beginning of a new season – particularly on a race boat. The helmsman and trimmers will get used to the setting, and it will be disruptive if the sensor has to subsequently be calibrated after a lot of sailing time.

Again, each individual system has its own calibration routines. The B&G H5000 has three variations. The first allows the navigator to compare directly with the GPS speed over the ground. This is only useful when there is absolutely no current.

Secondly, boat speed calibration can be manually adjusted as a percentage of a previous value. Or, for old school obsessives like myself, there’s a routine for correction against a measured mile.

Whatever system is used, some general rules can be followed to get a more accurate result. Set up when the water is flat; the logs measure the water flowing past it and are not too choosy whether the flow is created by the boat moving forward or up and down. If the boat is pitching it will record more distance than has actually been travelled.

Do the runs at fixed engine revs to keep the speed consistent. If using a measured mile, make sure the speed is the same at the beginning and end of every run – otherwise the acceleration will affect the results – so don’t slow the boat during the turn between runs.

Always steer as straight a line as possible between the chosen distance marks. If it is a proper measured mile then the chart will provide the bearings.

Any wavering from a straight line means the log will measure extra distance that will not be accounted for in the calibration calculation.

And finally, if the measured mile is in a tidal area then three runs are required to eliminate the tidal error and get an accurate calibration.

Apparent wind angle

The only real calibration possible for the apparent wind angle is symmetry on both tacks. The critical thing is to set this up on a day when there is very little or no wind sheer – usually a day with a well-mixed, gradient (not thermal or sea breeze) wind.

Apparent wind speed

It’s impossible to do much with this one, unless you’ve got access to a wind tunnel! If you have concerns ask the dealer or manufacturer, as they should be able to check the sensor.

On a calm day set the boat up with slack warps in the dock and put all the gear in its normal sailing position – including boom and spinnaker pole on the centre line. Whoever stays on board should also stand on the centreline while they read the heel meter.

Under these conditions the heel angle should read zero; if it does not then adjust it till it does, either with a software calibration or by physically moving the unit.

First published in the July 2019 edition of Yachting World.

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What range of heel angles do you consider optimum?

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I think my boat is initially tender, but then seems to take a set around 30 degrees (close hauled to beam reach). I've been trying to sail her at less than 25 degrees heel. What heel angle do you try to stay within? At what angle is a knockdown becoming a risk? At 30-35 degrees there is NOT excessive weather helm. I guess I am thinking that I should learn to sail her at greater angles of heel, rather than always reducing sail to stay within 25 degrees. This is an older, IOR-inspired design with moderate beam (10ft) for her length of 31ft. The hull is also rather round so there is not as much form stability as with a newer boat.  

Enough heel to achieve hull speed. If you are not sailing at hull speed, you need more sail. Upwind, my boat is at about 20-30 degrees to hit hull speed. Here is 6.7 knots on a Pearson 28 (24 foot waterline) at about 25 degrees:  

On my current boat if I'm hitting 20 degrees I thinking about reefing, on my last the same was about 30 degrees. That is difference between a 1988 and 2001 boat design! far as what "optimum" is think I would consider than to be 0 degrees  

Different hull shapes want different amounts of heel. Optimum for one guy, isn't optimum for you. 30 seems a little extreme, even for an IOR wagon, but I don't know doodly-squat. All I know, is that my Pearson 30 is "in the groove" at 20 degrees.  

So we were in "the slot" yesterday, and it was gusting 30 kts apparent. We had a double-reefed main, and the 83% jib up. The heel angle was up to 30 degrees. My instinct was to reduce sail, but the problem is that I hate furling the jib partially, because of the lousy shape that results. This is a frequent issue I encounter with this masthead rig, which is the huge jib with no easy way to reduce the size of it.  

this is completely boat design specific, absolutely no way to give a middle ground angle here a tender alberg boat design doesnt have the same angle as an ior, likweise the ior boat isnt going to have the same angle as a new beamy stern clorox box and likweise that boat isnt going to heel the same as an open 60 horses for courses I will say this...test your boat, acheive hull speed and any angle or heel after that will be useless or power "wasted" if you will. BUUUUUUUUUUUUUUUUUUUUT if you have a boat with big overhangs you actually get better as you heel more as water line increases....but then etc..etc..etc...  

The thing is that hull speed changes with heel because most waterlines increase. That being said, some increase more than others, so, as you say, it is boat design specific.  

capt vimes said: I do not understand the question.... Do you have all some sort of pendulars or electronical devise on board which give you a reading about your heel angle? Click to expand...

jaja I forgot the old flat is fast saying...its true for a reason we called saling at high heel angles when kids cowabunga sailing...an absolute blast to dunking the sides in the water, green water on the windows, all over splashing like crazy fun fun however its was slow and inffective as hell...  

albergs and the like are famous for being initially tender to 10-15 degrees and then love to stay at 20-25 like a freight train..and stay there thats just one boat design example... chose your poison  

That's nice than mine. Jealous now!  

I guess that OPs Bristol and my Bristol must have very different hull shapes - certainly we have very different displacements. We seem to be in the groove around 20°. More than that and everything feels like we are just too stressed. When I was young I used to think it was really cool to bury the rail. It felt like we were flying, but we weren't. Now we just do what feels right and gives the best speed.  

That and a bunch more leeway than one probably realizes.  

jzk : Interesting, I'll try that next time...  

slightly ior ish with small mains you cut with the jib and power with it too...so your better off getting maximum useable power off the jib in those winds and if needed spill some main... however 2 reefs in a small ior main means you are pretty much as depowered there without being useless so get the optimum jib for those winds... having said that its one of the reasons I dislike furlers...especially in high winds I just dont like them...as you get a bag with very little angle and shape not to mention very bad angle to the wind, and its very high up causing more than desired heel for the given winds... anywhoo  

christian.hess said: slightly ior ish with small mains you cut with the jib and power with it too...so your better off getting maximum usable power off the jib in those winds and if needed spill some main... however 2 reefs in a small ior main means you are pretty much as depowered there without being useless so get the optimum jib for those winds... having said that its one of the reasons I dislike furlers...especially in high winds I just dont like them...as you get a bag with very little angle and shape not to mention very bad angle to the wind, and its very high up causing more than desired heel for the given winds... anywhoo Click to expand...

Yes I'll definitely be trying that next time. I did kind of form the opinion that, if you're going to partially furl the jib, it's best to take a lot out of it instead of a little. Furling it down just a little results in a lot of bag, but taking out a load seems to result in a flatish sail again.  

too flat...they actually become riding sails  

You ain't leaning till someone is screaming! It really depends on what you are trying to do, are you racing and need the maximum speed, or just out for the day with the significant other? For maximum speed it might be good to do some testing with a GPS and see what works best. A good hand held GPS with speed over ground can give you a good idea, even a smart phone will work fine. For a day sail with the SWMO it is best to do what makes them happy! Every boat is different, and every sailor/crew has different tolerances. If it meant having the family out on the boat, and it takes 15 min more to get to the destination, so be it. I would rather make my crew/guests/family happy than worry about the last 2 tenths of a knot. And as far as a "knock down" I don't think you have to worry too much at the angles you are talking about. It may not have a lot of form stability, but the Bristol is not under ballasted. I would think you would feel it long before you were in any real danger.  

I don't measure the angle of heel to determine whether the boat is heeling excessively. I use the knotmeter. If it is visually apparent that the boat is beginning to heel alot, then I trim the sails to allow it to stand up more, and then watch the knotmeter to see if it speeds up. For a sailor, the ultimate goal is almost always to point high and foot fast, not to sail at a certain angle of heel. If you reduce the angle of heel, but the boat slows down and doesn't point as high, what have you accomplished? Your knotmeter will tell you more about your sailing efficiency than your inclinometer. Keep your eye on the prize.  

Every boat is different. A Bristol 31.1 might perform better upwind at about 25º of heel than at 15º. Bristols tend to be narrow boats that do better when they heel more. Heeling might help reduce wetted surface and improve boatspeed. On the other hand, maybe 15º is actually more effective than 25º since increasing the degree of heel might also increase leeway (your keel isn't sticking down as much when you're heeling: the more you heel, the more you're sliding to leeward.) YOU have to figure out what works best and what the most EFFECTIVE combination is. Reefing the main might reduce heel and speed, but increase your actual course made good to windward despite the slower speed. Leaving the main up, heeling more, but going faster may be the most effective route for your boat. How much heel works best may depend upon windspeed, boatspeed, and heading. There's no easy answer. That's what makes sailboat racing different from Golf. .  

dude arent we saying the same thing? jajaj Im confused now...Im agreeing with you...I have done it is what Im saying as well I was a sailing instructor and team coach down here for el salvador, racing dinghies and j24 etc... im not arguing for arguments sake here, we are in essence saying the same things... my current boat is an islander 36, ior design foresail driven masthead rig..as soon as I get the boat done I will try it...on this boat see what it likes best but judging from the islander 36 website, owners, racers and those in the bay area where I used to sail and there is a big fleet, my boat will love foresail changes and perfect jibe size for the wind...cause the little mainsail isnt the big decision maker here...jajaja  

So your boat with a little main likes headsail changes when it pipes up. My boat has a huge main, and it also likes headsail changes when it pipes up, but I do this by furling the jib.  

I keep my 100% jib on the furler. Having the big genny on is nice for light wind but for most conditions of 15 knots or so, the smaller headsail seems to be much more efficient than a partially furled up 160 genny. I guess I've made the decision that I'd rather have a sail fully set when wind is blowing than one that can give more speed in lighter wind. If I was not singlehanded and had a crew to change sails frequently, it would probably be most efficient to have a good selection of hank-on headsails. With a furler, it is a compromise one way or the other unless you're willing/able to change sails.  

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Boat safety 101: exploring the serenity and adventure of boating, the moment of truth – 6 signs you need a new boat, is it possible to wakesurf on a pontoon boat, 2024 aquila 47 molokai review, 2024 sea-doo switch 13 sport review, 2024 aspen c120 review, what is the appropriate degree of heel for a sailboat.

As a sailing enthusiast, it is imperative to understand the proper degree of heel for your sailboat. Heel angle refers to the degree of sideways tilt of the boat in relation to the water surface. It varies depending on different factors such as wind speed, sea state, sail plan and boat design.

The appropriate degree of heel for a sailboat is essential for safety, speed, and comfort. Generally, sailboats are optimized to perform best when they are slightly heeled to windward. This position allows the sails to catch the wind most efficiently and propel the boat forward while reducing resistance to the water. However, a sailboat that is heeled too much can reduce the performance of the boat, make it unstable or even capsize.

For most sailboats, a heel angle of around 10° – 15° degrees is commonly used. This range of heel enables the boat to maintain a good balance while also allowing the sails to catch the wind effectively. Nevertheless, it is possible to heel at a greater angle of up to 25° on larger boats with higher stability levels. However, heel angles over 25° should be avoided, or else the boat’s performance and stability may be compromised, and the risk of capsizing increases.

Several factors may affect the appropriate degree of heel for a sailboat. One of the most significant variables is wind speed, with stronger winds leading to greater heeling angles. The sea state also plays a role in determining the right heel angle, with choppy waters requiring a higher degree of heel. The sail plan and design of the vessel also affect the appropriate heel angle. Smaller boats with fewer sails may require lower heeling angles compared to bigger boats with complex sail plans.

Determining the appropriate degree of heel for a sailboat may vary depending on different circumstances. Nonetheless, maintaining a heel angle between 10° – 15° is considered the optimum range for most sailboats. It is essential to pay attention to factors influencing the ideal heel angle, including wind speed, sea state, sail plan and boat design. By maintaining the right heel angle, you can ensure a comfortable, safe, and speedy sailing experience.

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Ideal average angle of heel 20-30ft LOA

Discussion in ' Boat Design ' started by human 1.0 , Apr 8, 2011 .

human 1.0 Don't mess w/ Humanity

I am curious what people think the proper angle of heel should be across the board going to windward.  

gonzo Senior Member

There is no such thing. Each design type has an ideal angle of heel in different sea and wind conditions.  

"There is no such thing" Forget that closed-minded approach. This is an across-the-board inquiry. This is a survey, like the census, everybody who sails has an angle of heel that they like, that makes them smile. I want to know what that is, and then reverse-engineer all the rest from that number. The shape of the chine comes to mind as a direct influence, and I am wondering about the spill of the sail, whatever sail that might be.  

Lister Previous Member

This is no reverse engineering, it is a stupid question. Read Gonzo, he is right. Lister  

viking north VINLAND

There is no proper so to say, On my past very stiff broad beamed motorsailer she performed best at between 10 and 15 deg of heel. Thats where she balanced out nice with a little weather helm at max. speed. It's a boat characteristic thing and often it varys between so called identical craft and as such makes the reverse engineering difficult but I see your logic in thinking so.--Geo  

viking north said: ↑ There is no proper so to say, On my past very stiff broan beamed motorsailer she performed best at between 10 and 15 deg of heel. Thats where she balanced out nice with a little weather helm at max. speed. It's a boat characteristic thing and often it varys between so called identical craft.--Geo Click to expand...

Here is an example of engineering from the angle of heel, which for this transat is 8-10 deg: "to windward they are slow and sail on a heeled water line around 8 - 10 degrees before you add yaw" Link I wonder if "yaw" means they fall over to leeward as there is so much less buoyancy up forward on a floating pie slice like a transat.  

BATAAN Senior Member

As little as possible. Trim the boat to go, not heel.  

PAR Yacht Designer/Builder

The average angle will be from about 5 of degrees to windward to 30 degrees to leeward, depending on hull form, sail plan, ballast ratio live or fixed and about two dozen more variables. Of course you could refine this a bit more by "splitting the difference, so your target is 12 to 15 degrees. Of course it's ludicrous, but it's a number to reverse engineer from, though a profoundly poor way to engineer anything . . .  

Plank on edge cutters sail at 20-25 degrees on average.  

daiquiri Engineering and Design

human 1.0 said: ↑ Forget that closed-minded approach. Click to expand...

Frosty Previous Member

When the wife comes up wearing my dinner I know that its time to let out a bit.  

Thankyou Daiquiri - i wanted to say something about that but wasn't sure what it meant version 0.1 and 0.2, or how to go about it. If it's using members postings as a sort of comparison or competition I ask Human 1.0 to please not involve me in such and to please retract and remove that part of the post. I'm sure it was just a knee jerk reaction which we can be all guilty of from time to time, but If one has a beef with a post then i feel it should be a one on one situation as it is uncomfortable to be put in the middle. All posts are opportunity to learn for both sides, in technical information and etiquette myself included.  

HakimKlunker Andreas der Juengere

BATAAN said: ↑ As little as possible. Trim the boat to go, not heel. Click to expand...

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Petros Senior Member

best angle of heel is zero, you get the most sail in the wind, and the keel is most effective. Hence, the catamaran. Even they heel a bit, but they come much closer than any mono-hull. some of the modern racing mono-hulls have very long weighted keels that can be swung to the side can also have very small heel angle. Now that is engineering to the "ideal" heel angle! I think each design settles into a heel angle that is best for it, it was not intentionally designed to a certain angle of heel. As pointed out, there are a lot of different factors that affect it, and the designer usually selects the various design elements to meet other higher priority design goals, and the best angle of heel just falls out of the those choices. It is indeed silly to design a boat to hit a certain "ideal" heel angle, it would be a very poor choice to compromise ALL other aspects of a sailboat design to meet a certain heel angle.  

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Learning to Sail: Heeling Over

On the other hand, if you sail dinghies or other unballasted boats then you may capsize if you heel over. It’s part of the fun of sailing that type of boat! When you train to sail dinghies you learn how to quickly and easily right the boat. To start with, if you are slightly nervous, then we suggest learning to sail on a solid keel boat like Chao Lay .

Learning To Sail: What Does The Keel Do?

The keel is a flat blade that is attached to the bottom of the sailboat. It has two main purposes:

• It prevents the boat from being blown sideways by the wind, and
• It holds ballast that helps to keep the boat the right way round.

Be advised that you need to know the depth of your keel to safely navigate in shallow water.

Learning To Sail: Will We Capsize?

Keel boats have plenty of ballast to keep them upright, even in the most extreme conditions. All sailing boats will heel over, and you may even get a wave or two over the side. Don’t be alarmed as this is just part of sailing; keel boats are designed to heel and many skippers say it’s the most exciting part. Cleverly, keel boats were designed using basic physics:

• The ballast is located well below the waterline in the keel. If the boat heels over then the leverage increases. For example, you can compare this to holding a weight in your hand. As you raise your arm straight out from your body, the weight feels heavier the further your arm moves upwards. This is exactly the same as the ballast taking effect when a boat heels over.

It makes sense that a keel boat is very difficult to capsize when these two effects work together (reduced wind pressure on the sails and the ballast working to right the boat). Simply, trust the science and enjoy the experience!

Learning To Sail: How Far To Heel Over?

This is another question we get asked by students. Basically, you want the sailboat to move through the water as efficiently as possible. If you keep a steady heel angle, the blades and sails will efficiently glide through the flow of the water and wind. Keeping the angle consistent is important; there are three things you can adjust to ensure this:

• Sail trim, and
• Placement of weight.

The ideal heel angle is different for each boat. Generally, keel boats should be sailed somewhere in between 10 to 30 degrees.

Our next blog will look at sailing techniques used when  racing in regattas , taking an in-depth look at the three considerations listed above. Until then, check out these great books from the RYA:

Buy RYA Start to Race at the RYA Shop

Stylists and designers share 8 shoe trends that are in and the 4 that are out for spring

• Business Insider asked three fashion experts to share which shoe trends are in and out for spring.
• Clogs and mules are easy, comfortable, and popular trends that are on the rise this season.
• On the other hand, chunky platforms and "dad" sneakers are falling out of style.

With footwear prices increasing in recent years, you'll want to make sure you're investing in styles you won't regret.

Business Insider spoke to two fashion designers and a stylist about which shoe trends are in and out for spring.

Here's what the experts said.

Ballet-flat-inspired sneakers are in

Ballet flats have been trending throughout past seasons, but the classic, ultra-feminine silhouette has a new spin: sneakers.

Ballet-flat-inspired sneakers with openings at the top of the shoe and strap-like laces are coming to the forefront of high fashion, according to fashion designer Jarrah Webster .

"The runner-like soles are something that's being brought back when it comes to mixing femme-wear product shoes with menswear," Webster told BI.

Classic dress shoes are coming back

As minimalism and capsule wardrobes become more popular, footwear trends are also going back to the basics, according to celebrity stylist Semarah Gabrielle .

It's time to bring back the classic dress shoe, she told BI.

"Like the pointed-toe pump for women, we are going back to the basics for men," she said.

Mules are a comfortable, chic, and popular shoe

Comfort is at the forefront of fashion, and mules are a perfect choice because they have no back, according to fashion designer Jazmin Monét .

She told BI that mules are a great "statement shoe" that can elevate a look. W ith so many styles and colors, this versatile silhouette can be dressed up and down.

Military-inspired combat boots are staying in the rotation of trends

Combat boots have been popular for decades, and the trend isn't slowing down, according to Webster.

"These are always in my rotation, and I think workwear is such a big influence in today's trends," he said.

Some combat-boot styles, such as boots with a steel toe, are also very functional.

2010s wedges are back in the spotlight

Again, comfort is in. Wedged heels are super reminiscent of the 2010s , and according to Gabrielle, they're gaining popularity yet again.

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"Ten years later, wedges are back. They are comfortable heels and great for spring and summer," she said.

Clogs are also an easy, trendy shoe choice this spring

More and more people are discovering the comfort, ease, and versatility of wearing clogs. And the culturally inspired silhouette is becoming popular in different worlds of fashion, according to Webster.

"They play homage to a lot of cultures, and I believe the shape, silhouette, and material of these are so versatile," he told BI.

Stiletto heels remain a popular, stylish shoe

According to Monét, a stiletto heel will never go out of style.

"Stilettos are a staple sleek heel that can make the simplest dress pop, and they'll never go out of style," she said.

The high-heeled silhouette is great for dressing up a casual outfit or making a dressy outfit even better.

Wrestling shoes create a unique and uniform style

Another footwear silhouette that's a blast from the past is the wrestling shoe, said Webster.

"These early-2000s wrestling shoes, from brands like Adidas, Puma, and Reebok are very beautiful," he said. "They allow for a very uniform fit and feel, and I've even seen them worn with more feminine looks."

The slim, lace-up boot-like shoe comes in feminine and masculine silhouettes and can help you create a sporty (but chic) look.

On the other hand, chunky platforms are declining in popularity

Chunky platforms are on the way out as comfort becomes a priority, said Gabrielle. Instead, people are opting for a lightweight silhouette that is easier to manage for a day or night out.

"2024 is the year of comfortability — we're saying goodbye to the chunky platforms for a night out," she told BI.

The obsession with 'dad shoes' is declining

Although the chunky "dad shoe" silhouette was super popular this time last year, they're falling out of favor. People want a much sleeker look, said Gabrielle.

"We're moving toward a more softer way of dressing. They're cute and versatile but, in my opinion, have been way overplayed for years," she said.

Boat shoes are being left in the past

Although boat shoes — canvas or leather shoes with rubber soles — have had their moment, they're likely not making it into this upcoming season, said Gabrielle.

She recommends only wearing them for literal reasons.

"They're the cousin to the loafer but not as elevated," she told BI. "The boat shoe was huge in the 2010s, but they don't go with everything and personally only should be worn if you're on a boat."

'Hypebeast' sneakers are nothing more than a collectible item these days

Hypebeast describes the subculture around limited-release, exclusive fashions — particularly when it comes to sneakers. But, Gabrielle said, retro and release-driven sneakers may be better to collect than wear this spring.

"Sometimes the styles aren't practical and hard to wear for everyday use," she said. Plus a lot of limited-release styles aren't trendy for long.

"They have a lot of attention leading up to the release but then slowly fade once they are released," she added.

Watch: 10 functional clothes and accessories for holiday gifting

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• Thread starter freeheelbillie
• Start date Oct 22, 2016
• Catalina Owner Forums
• Catalina 30

freeheelbillie

Whats the ideal heel for a 30' 1992 mark II wing keel, tall rig?  

hull speed and as upright as possible....and that all depends on the wind and the amount of sail area you have exposed  

Depends on what you mean by ideal. Optimal upwind sailing will have heel angle increase as the breeze does. Boats with published polars will also show heel angle for each wind speed band. Just cruising? Keep it flat.  

You determine it by your comfort. The amount of your sail up and trimming can get you on your side or upright. It's determined and controlled by you.  

Not sure about ideal. But it is sure fun to have a sail boat on a bit of heel biting in to the breeze and waves.  

Find the groove and live there. The groove is defined (in my book) as that point when sailing that the boat is moving along nicely and the helm is not fighting back. She is in her groove! You will know it when you achieve it.  

Hello Below

Jackdaw said: As an example of ideal upwind heel, look at the line Up.Heel for typical heel angles for increasing wind. Click to expand

Hello Below said: Jackdaw, any chance of getting the source for this data so that I can make some sense out of particularly the bottom 2 tables? Click to expand

woodster said: hull speed and as upright as possible.... Click to expand

David in Sandusky

Thanks, Jackdaw, I really learned something from your comments and link. Conforms well to my experience on our '77 h27.  

Jackdaw said: You can find the entire document here. Click to expand

I used to have a Hunter Legend 35 and raced it quite a lot. Marblhead, Boston, Buzzards Bay, Annapolis, Palm Beach. ft. Lauderdale. Key West, Puerto Rico, St. Croix, St, Thomas, BVI. One thing became very obvious, with a 4.5' draft the wing keel worked better with 15-20 degrees of heel. The flat bulb/wing keel would keep the boat from side slipping, less than a J 30 that owed me time. I was able to track higher than the J with a much better VMG. Down wind with a chop it dampens the motion giving you more forward speed. When cruising, use the small jib, reef, whatever and make it comfortable. If you reall want to go upwind, then heel her.  

On my boat, the optimum angle of heel is 23 degrees. That is where I get the most speed out of the boat; a balance of power from the sails and drag from the rudder due to weather helm. When going to a windward mark, I try to keep the heel down to 15 degrees to reduce sideways drift and point as high as I can. When reaching drift is not a concern as you just adjust your heading. As a cruiser though, I do not push the boat anymore. 6.5 knots is as fast as I want to go for more than an hour. When you are 1500 miles from the nearest land, getting there in one piece is more important than getting there fast.  

Its important to remember that the 'ideal' angle of heel for any boat will ALWAYS be a function of true wind speed. In general, flatter is better. The foils simply work better. The why is any heel ideal? The heel angle is a function of the rig/sailplan powering up, and working against the keel's Righting Moment (RM). That's a good thing as thats where the boat gets its power. But always remember that when the boat heels everything is less efficient. Its a trade-off that generally says the the more wind, the more heel. Up to a point!  

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