yacht capsize ratio

What Is Capsize Ratio And How Is It Calculated?

With so many different terms and calculations in the sailing world, it’s no wonder that capsize ratio is confusing.

Have you ever been on a boat and had it suddenly turn over? Or maybe you’ve seen a boat capsizing on TV. Either way, it’s not a pretty sight and you might be eager to know your boats capsize screening ratio before you head out for a sail.

But what exactly is a capsize screening and how is it calculated? Keep reading to find out.

Table Of Contents

What is capsize ratio, how to calculate capsize ratio.

• What’s A Good Capsize Screening?
• Why Is Capsize Ratio Important?

Capsize Ratio Calculator

Capsize ratio is a term used to describe the likelihood of a sailboat recovering after it has capsized. It gives an indicator as to whether or not the boat will right itself after being fully inverted.

This term was developed after the tragic  Fastnet race disaster in 1979, where a storm destroyed several yachts and caused 19 deaths at sea on the last day of the race.

After this disaster, tests were done to try and determine a calculation that could be used to determine a boat’s ability to right itself after capsizing, and therefore give an indication of whether or not it is suitable for offshore sailing.

You can calculate the capsize screening of your boat yourself using a simple formula.

To calculate the capsizing volume using this formula, you need to know several key variables about your boat: The displacement in pounds and waterline beam.

Once you have these values, you can use a simple equation to determine your capsizing volume in tons as well as your capsize ratio.

Capsize Screening Formula = Beam / ((Displacement/64.2)1/3)

This formula doesn’t factor in the location of the ballast and there forefore the centre of gravity, or the shape of the hull. It also doesn’t take into consideration things like weather conditions which can play a significant part in whether your boat will right itself or not.

What Is A Good Capsize Screening Ratio?

There isn’t really a good or bad figure, they just mean slightly different things which we’ll cover more below.

The way the calculation works, is that the lower the value, the less likely a boat is to capsize. The cut off for many offshore races is a ratio of 2 or under, indicating that boats with a ratio over 2 are more likely to capsize.

While calculating your boats overall capsize ratio may seem like a complex task, it’s an important indicator in determining whether or not your boat is suitable for offshore sailing. It’s a great tool to use before setting off on your next adventure.

Why Is Capsize Screening Important?

Unless you plan on long, offshore passages, capsize ratio isn’t actually that important.

It simply gives a rough indication of whether or not your boat was intended for offshore use where you’re more likely to encounter the kind of waves that might cause a capsize.

A beamy design with a capsize screen over 2 has some real advantages for coastal cruising:

– Higher form stability, supporting more sail as winds move up to 20 knots.

– More interior room for living aboard.

Coastal cruisers can usually return to port before conditions build breaking waves tall enough to capsize the boat.

If you’re not great at maths like me, or you want to calculate the capsize ratio for multiple boats and are looking for a way to save some time, then you can use a capsize ratio calculator to work it out for you.

You can also find the capsize ratio along with a load more data for almost every boat on Sailboat Data .

Conclusion: What Is Capsize Screening And How Is It Calculated?

Capsize ratio is just one tool that can be used to determine a boats suitability for sailing offshore. There are many factors that influence a boat’s capsize ratio, such as its design, loading, and weather conditions.

The capsize ratio of a boat is a useful tool, but isn’t an absolute, so it’s important to know your boat well before heading off on a longer passage away from the safety of land.

Hopefully this has help to explain capsize ration. If you’re looking for more tips and inspiration on all things sailing then make sure you follow us on social media, where we regularly share new articles and information on our lives aboard.

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Comparing capsize and comfort rates of boats

• Thread starter Richard Marble
• Start date Mar 16, 2004
• Forums for All Owners
• Ask All Sailors

Richard Marble

Here is a list of boats to compare. I have a 1981 Hunter 27. I know from sailing my boat that it feels very stable when it is rough out. I have been comparing the capsize factor and the comfort factor of my boat with other boats. Here is what I have found."Note" anything with a capsize factor over 2 I did not do a comfort factor on as they are more able to capsize so I didn’t figure it made much difference if you were comfortable. What surprised me is that a Hunter 27’s capsize and comfort rate is right up there with a Hunter 35.5 and is better than an Islander 32!!!If your boat is not here and you want to check it go to the related link.Hunter 27 1981Capsize factor of -1.94Comfort factor - 23.39Hunter 31 1985Capsize factor - 1.9Comfort factor - 24.55Hunter 28 1986Capsize 2.21 Not acceptableHunter 30 1983Capsize factor of -1.89Comfort factor - 25.21Hunter 33 1981Capsize factor of -1.86Comfort factor - 25.56Hunter 35.5 1995Capsize factor of -1.97Comfort factor - 24.57Irwin Citation 31 1979Capsize factor of -2.09 Not acceptablePearson 31 1978Capsize factor - 2.03 Not acceptableAllied Seawind 30 1965Capsize factor of - 1.62Comfort factor - 36.86Bristal 32 1966Capsize factor of - 1.74Comfort factor - 32Endeavour 32 year?Capsize factor of -1.76Comfort factor - 30.25Islander 32 year?Capsize factor of - 2.03 Not acceptableIslander Iona 32 year?Capsize factor of -1.9Comfort factor - 23.17Alberg 30 1968Capsize factor of -1.71Comfort factor - 30.97O’Day 32 1977Capsize factor of -1.91Comfort factor - 25.38Pearson 323 1983Capsize factor of -1.74Comfort factor - 30.88Kettenburg K32 1978Capsize factor of -1.86Comfort factor - 27.76  

Trevor - SailboatOwners.com

Another fun Sail Calculator Another fun Sail Calculator with an extensive database of boat models can be found at the Related link below. The program outputs a number of different categories in a bar chart format in a separate window. But remember, these are just numbers!Have fun,Trevor  

Be Careful With The Numbers Looking at these numbers are all well and good but they are derived from simple formulas and don't take into account many factors. And, additionally, how you setup your boat will change the numbers.For example:Capsize Ratio = Beam / (Displacement / 64)**0.333 Notice the only factors involved are Beam and Displacement. This means that, for the same displacement, a boat with a light-weight construction and a deep fin keel will have the same number as boat with heavy construction and a shoal-draft keel.To test what a few hundred pounds difference makes in displacement just run it through the formula and you will see that it makes a difference. If that little change in displacement makes that much difference just imagine what a difference taking into account the center of gravity and the lever arm would make. Think about that 8 or 9.9 hp outboard hanging on the stern rail, life raft and dingy on the coach roof, jerry cans of gas and water lashed to the life lines, etc.. Your numbers just changed big time.The formulas are "no brainers" but one needs to use a lot of judgment when using them.They make a good starting point for discussion, though, if you know what is behind them but don't treat them as gospel.  

Rough Numbers As John indicated, the MCR & CR don't consider all the numbers & variables, and should only be used for a very rough preliminary consideration of very similar boats.For instance (I'm paraphrasing Jeff_H from another forum):An extreme example: You could move a significant weight from a boat's deep keel to it's masthead, without affecting the formulaic outcome (very different boat realities, but same resulting ratios).Regards,Gord  

Richard A. Marble

Is there a better formula out there? I couldn't agree more. I wonder if there is a formula that takes the draft and keel weight into consideration. If there isn't why does'nt someone come up with one? It would be much better I would think.  

Isn't the CR really a righting ratio Richard, I am going to go off and confirm this info, but wasn't the capsize ratio developed by Ted Brewer to be an indication of a boats ability to recover from a capsize (the 180 position) and not specifically to be an indication of its initial stability? The factor favours less beamy boats which have less initial stability when upright, but when turned turtle the lack of beam means they can be uprighted more easily. And of course the greater and deeper the ballast the easier the righting process.I seem to recall Ted pointing out that today's modern beamy boats may not be able to right themseleves when inverted due to their wide beam.Kevin  

Laura Bertran

I've seen different numbers... ...right on this site. The capsize factor for a Hunter 31 is 2.13.  

The capsize screening formula is useful because wide light boats don't roll back up as quickly as narrow heavy boats. There are other numbers that can be calculated to give the range of positive stablity. It is odd that boat manufacturers almost never include this data. But for the few boats that I've compared if the CSF is low the boat is generally considered seaworthy. But even the range of positive stability may not be a better indication in that capsizing is a dynamic event and the RPS is a static measure. The CSF came about by looking at boats that survived the Fastnet?? disaster as opposed to those that didn't. It is an empirical observation rather than a theoretical calculation.  BTW I have a book that has a photo of a beamy fin keeler in the turtle position with the crew standing on the hull. Yes the keel is still attached!! Once that mast is underwater with sails it would take a lot to bring it back upright.  

newly anonymous

does not compute That capsize screening formula is almost universally criticised for being overly simplistic. It does not take into consideration the all-important ballast/displacement ratio, nor does it factor ballast/draft. If my boat displaces 20,000 pounds, it makes a tremendous difference whether 6,000 of those pounds are in ballast or 8,000 are. My H410, which displaces 20,000 pounds, has a bulb keel of 7,500. Surely this bulb keel gives it superior capsize stability than a fin keel would, but the formula doesn't take that into consideration. Neither does it factor whether I have the deep keel version or shoal draft. To simply factor beam verses displacement is ludicrous.  

Please give me an example of a cruising boat generally recognised as a seaworthy blue water cruiser that has a CSF greater than 2!!!!Check out allied seawind,Pacific seacraft,swans,cape dorys, etc etc I haven't done an extensive survey but every one that I have looked at had a CSF of 1.8 or less.  

Jeff M21319

IMHO, the calculation is so simplified... that it is useless. From an engineering viewpoint, so many relevant variables have been left out that any conclusions drawn using the formula presented are essentially false. While beam and displacement are important numbers, they certainly aren't the only ones that need to be considered and given a place in such a complex analysis. Kind of reminds me of the old 'skid charts' the police would use to determine the speed of a vehicle immediately prior to a colision. They would take the length of a skid mark, determine the type of road surface and then look it up on a little chart to get the estimated speed. No accounting for such things as vehicle weight, tread width, condition of tread, inflation pressure, etc. was done.  While I'm certainly not a naval architect, it would seem that determining a boats inherent ability to self-right after going inverted would require complex computer modeling, tank testing and perhaps other sophisticated methodology to get anywhere near a correct answer. Even then, one would have to look at variables such as type and size of sails aloft during the event, actions taken by the crew immediately prior to and after the event and a myriad of others. Sorry, but I just can't buy into a calculation so inherently flawed. P.S. Has anyone ever heard of or contemplated something along the lines of an auto-inflating PFD that would be mounted at the top of the mast and deploy after being submerged? I wonder what (if any) effect this would have, given a few hundred pounds of positive bouancy, on initiating a self-righting action? Perhaps I'm crazy (although it's never been proven in court!) but would something along the lines of a 4' diameter inflatable mooring ball tied to the top (bottom) of an inverted mast do much to get a 10 ton boat headed back onto her feet? What if it also had, via some mechanical means, the ability to 'blow' the main and jib halyards to remove the resistance of the sails to the righting movement? Just wondering.  

Just asked Bob Perry on cruising world's BB He didn't put much value on the CSF in and of itself. He said that bigger is better in that a longer boat is less likely to capsize. He also said that for cruisers that if you stay away from radical designs and have a moderate beam and displacement/length or 220 or better you'll probably be alright. But if you think about it a heavier boat D/L>220 and a moderate beam will probably give you a CSF of less than 2.0.Bob Perry please forgive me if I misquoted. My only attraction to the CSF is that it is a readily available number to compare boats. If you look at SA/Displ,Disp/wll, motion comfort ratio beam/length,PHRF etc you get an idea of what the boat is like. Of course all of these numbers are indications of how the boat probably will perform. Ideally you would have the time and money to hire an expert designer to evaluate the boat. But for some boats this would cost more than the boat!!!!!!  

So the verdict is According to what I’m reading, This capsize formula is pretty much worthless to really determine if your boat will capsize or if it will right itself. That said, generally speaking a boat with a higher number is probably less capable of staying upright than one that has a lower number. So when someone is looking at boats, I guess, use this formula but keep in mind that the lower the keel and the heavier the keel the better. Also you should keep in mind mast height and how much freeboard there is above the water line.Now why doesn’t someone come up with a better formula? While it may not be perfect I’m sure it could be better than this one.  

henkmeuzelaar

Uncomfortable truths about "comfort factors"..... What is the point of even discussing the value of such dimensionless empirical numbers when one is unlikely to find two sailors who completely agree on what "comfort" (or rather: "comfortable motion") at sea really is? Just try to start a rational discussion on this topic between avowed mono- and multi-hullers and you will soon see the futility of such an exercise.Perhaps we should all remember one other fact as well: there is currently no model (i.e. quantifiable level of understanding) that even begins to describe the dynamic behavior of a sailing vessel at sea. If that sounds like a bit of an exaggeration, just consider the fact that current models for boat speed at different points of sail and wind strengths are only valid for flat water! In other words, no one is even able to fully describe what the effects of seastate on something as straightforward as BOAT SPEED are...... IMHO, anyone who accepts the claim that some magical formula can predict the effect of seastate on something as complex as "comfortable motion in a seastate", while at the same time acknowledging that our current level of understanding is insufficient to predict something as comparatively simple as the effect of seastate on boat speed, would appear to have some issues to deal with that fall well outside the scope of this board.Have fun!Flying Dutchman  

You're Right Richard - Take With A Grain of Salt By jove I think you've got it! These formulas make a good starting point for discussion purposes.If nothing else, if your post got you thinking about what's going on that's good. You've started asking questions - that's good. Not taking everything hook-line-and sinker, that's good.I'm thinking about my own boat which is much the same as the Hunter 35.5 and has an aluminum toe rail. The Toe rail is bolted onto a flange on the hull and deck and sticks out about 2 or 3 inches. The beam is the width to the outside of the toe rail. So, do you plug in the manufacturers published number for the beam or use the beam measured to the outside of the hull? At 2" x 2 that's 1/3 of a foot, 0.333. At 3" x 2 that's 0.500 feet. Hey! That's significant!Then there are the other things that don't even fit "The Formula", like how one loads the boat, things one can do to rectify a bad situation (creative flotation devices were mentioned). So the point is there are a lot of variables that aren't in the formula. I guess if a point can be made that this MAY true with all the other formulas too so take the formulas with a grain of salt. The PHRF formula isn't exact either and it incudes many more variables but for speed on a race course, as a rule, it gets pretty darn close. There are exceptions, though, such as the handicap factor for a fixed-blade prop.Not only should one think about and question the forumulas, one should always be thinking when you're on the boat. Things happen and you have to be creative with ways to work your way out of a bad situation. Whether it's a squashed pinkiy up the inside passage (this happened to the Pardey's), getting a boat up-righted, or just getting between those two boats coming toward you in a narrow channel. We are really on our own out there, some times more than others, and you can't necessarily just call 911 to be taken care of.Bottom line - use the info with a grain of salt and think for yourself. And .... if your boat isn't reasonably water tight the best number in the world won't mean a thing.Now go out there and have fun.  

Henk Is your boat an FD=12?Dennis  

Nah, HL43. Tell us about your Windship, though! Flying Dutchman is just the nickname my crew gave me (probably because I am such a nice guy ;D). For the past decade, or so, I have been using this handle faithfully in order not to give anyone a chance to change it into Captain Bligh......The name of our Hunter Legend 43 (hull #1) is Rivendel II. Just type "Rivendel" under Search as far back as Phil's archives go these days and you will get a pretty good idea about what she's been up to.Have fun!Flying Dutchman  

Fred Ficarra

CSF I still believe in formulas that are used with caution. Take my chick screening formula as an example.weight X height in inches/ageX150. Usually women with a CSF of 2.2-1.8 are acceptable. If the number gets too high she is too fat or young. If the number gets too low she is too old ,short or skinny. If I throw in a couple of qualifying limits the results are better. Say older thatn 18 and younger than 35. But then you might get a perfect number and the girl be unacceptable for other reasons such as she doesn't like old farts!!!!Example a 62" woman weighing 120#s and 25 years old = 1.98 if she is 55 that number changes to =0.90 which is clearly an unacceptable number. Maybe I should factor in red hair and a large bank account???? But heck it's hard enough to get a woman to devulge her weight and age!!!!!!! Maybe a beer factor where .25 is added or subtracted for each beer consumed in the last hour????  

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Calculating Sailboat Design Ratios

Without having to wrestle with the mathematics.

Not only do the Sailboat Design Ratios tell us a great deal about a cruising boat's performance and handling characteristics, they also enable us to make objective comparisons between individual designs.

Here are the five main ones in common use by yacht designers and the formulae from which they are derived.

Five Key Sailboat Design Ratios:

The displacement/length ratio.

D/L Ratio = D/(0.01L) 3

Where D is the boat displacement in tons (1 ton = 2,240lb), and L is the waterline length in feet.

The Sail Area/Displacement Ratio

SA/D = SA/D 0.67

Where SA is sail area in square feet, and D is displacement in cubic feet.

The Ballast Ratio

BR = (B/D) x 100

Where B is ballast in lbs, and D is displacement in lbs.

The Capsize Screening Formula

CSF = 3 √(Bm/D)

Where Bm is the maximum beam in feet, and D is displacement in cubic feet.

The Comfort Ratio

CR = D/[0.65 x (0.7L 1 +0.3L 2 ) x Bm 1.33 ]

Where D is displacement in pounds, L 1 is waterline length in feet and L 2 is length overall in feet, and Bm is the maximum beam in feet.

Problem is, can you always trust the ratios published by the manufacturers? The answer, sadly, is "no".

So when you think you're comparing like-for-like, you may not be.

But let's be generous, it's not always an intentional deceit - there are two main parameters where ambitious data can lead to misleading Design Ratios. These are found in the manufacturers' published data for displacement and sail area .

In almost all yacht manufacturers' published data, displacement is quoted as the ‘light ship’ or unladen weight displacement.

This is unrealistic, as the laden weight of a fully equipped cruising boat is much higher.

As displacement is a key parameter in all of the Design Ratios, the laden weight should be taken account of when comparing one boat’s ratios with those of another.

Published SA/D ratios can similarly be misleading as some manufacturers, keen to maximize their vessels’ apparent performance, quote the actual sail areas which could be based on a deck-sweeping 150% genoa. On paper this would compare unjustly well against a competitor’s boat that has the ratio calculated on the basis of a working jib. 

Making an objective comparison between two such sets of SA/D ratios would be impossible.

An objective comparison can only be made if sail areas are calculated on the same basis using the J, I, P and E measurements as set out in the above sketch.

So now to the point...

What we have here is our  Interactive  S ailboat Design Ratio Calculator , which does all the calculations for you instantly and avoids all the pitfalls described above. The pic below is where you would enter the dimensional data on the downloaded Design Ratio Calculator :

The following pic shows the Design Ratios which are automatically calculated in the blink of an eye!

Download the Sailboat Design Ratio Calculator...

The  Interactive  Sailboat Design Ratio Calculator is  accompanied by a free eBooklet 'Understanding Sailboat Design Ratios' which will help you make sense of the numbers. 

Our 'Sailboat Design Ratio Calculator' takes all the hard work out of calculating the numbers and  will provide a valuable insight into a sailboat's performance and handling characteristics.

We make a small charge of $4.99 for this useful tool as a contribution towards the costs of keeping this website afloat. 

This  Sailboat Design Ratio Calculator and eBooklet  comes with a No-Quibble Guarantee!

Sailboat-Cruising.com's Promise to You:

"I'm so sure that you'll be absolutely delighted with your purchase that I'll refund in full the price you paid if you're dissatisfied in any way" , promises

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So what are you waiting for?

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Calculations

Sail area / displacement ratio.

A measure of the power of the sails relative to the weight of the boat. The higher the number, the higher the performance, but the harder the boat will be to handle. This ratio is a "non-dimensional" value that facilitates comparisons between boats of different types and sizes. Read more.

SA/D = SA ÷ (D ÷ 64) 2/3

• SA : Sail area in square feet, derived by adding the mainsail area to 100% of the foretriangle area (the lateral area above the deck between the mast and the forestay).
• D : Displacement in pounds.

Ballast / Displacement Ratio

A measure of the stability of a boat's hull that suggests how well a monohull will stand up to its sails. The ballast displacement ratio indicates how much of the weight of a boat is placed for maximum stability against capsizing and is an indicator of stiffness and resistance to capsize.

Ballast / Displacement * 100

Displacement / Length Ratio

A measure of the weight of the boat relative to it's length at the waterline. The higher a boat’s D/L ratio, the more easily it will carry a load and the more comfortable its motion will be. The lower a boat's ratio is, the less power it takes to drive the boat to its nominal hull speed or beyond. Read more.

D/L = (D ÷ 2240) ÷ (0.01 x LWL)³

• D: Displacement of the boat in pounds.
• LWL: Waterline length in feet

Comfort Ratio

This ratio assess how quickly and abruptly a boat’s hull reacts to waves in a significant seaway, these being the elements of a boat’s motion most likely to cause seasickness. Read more.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam 1.33 )

• D: Displacement of the boat in pounds
• LOA: Length overall in feet
• Beam: Width of boat at the widest point in feet

Capsize Screening Formula

This formula attempts to indicate whether a given boat might be too wide and light to readily right itself after being overturned in extreme conditions. Read more.

CSV = Beam ÷ ³√(D / 64)

The theoretical maximum speed that a displacement hull can move efficiently through the water is determined by it's waterline length and displacement. It may be unable to reach this speed if the boat is underpowered or heavily loaded, though it may exceed this speed given enough power. Read more.

Classic hull speed formula:

Hull Speed = 1.34 x √LWL

Max Speed/Length ratio = 8.26 ÷ Displacement/Length ratio .311 Hull Speed = Max Speed/Length ratio x √LWL

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Capsize Screening Formula for Boats and How to Measure It

Boating enthusiasts understand the thrill of being out on the water, but with adventure comes responsibility – especially when it comes to boat stability and safety. The concept of boat stability and the risk of capsize are crucial factors for anyone navigating water bodies. In this article, we’ll delve into a tool that holds the key to understanding and evaluating a boat’s stability: the capsize screening formula.

This formula is more than just a mathematical equation; it’s a powerful tool that provides essential insights into a boat’s potential for stability or vulnerability. As boaters, understanding the capsize screening formula and its components can greatly contribute to informed decision-making and safer voyages. Join us as we explore the depths of this formula, decode its components, and highlight its significance in ensuring enjoyable, secure boating experiences.

The Foundation of Boat Stability

When it comes to boating, stability forms the very foundation of a safe and enjoyable experience on the water. Stability refers to a boat’s capacity to maintain an upright position and resist tipping or capsizing, even in the face of challenging conditions. Understanding stability is essential because it directly impacts how a boat responds to waves, wind, and the movements of passengers onboard.

Stability isn’t just about comfort; it’s a critical factor in preventing capsizing – a situation where a boat overturns and potentially endangers passengers and crew. Ensuring a boat’s stability is paramount for maintaining control, avoiding accidents, and promoting confidence in boating endeavors. One powerful tool that aids in assessing a boat’s stability and potential capsize risk is the capsize screening formula. In the following sections, we’ll explore this formula’s components, how it works, and why it matters for safe boating practices.

Introducing the Capsize Screening Formula

The capsize screening formula is a mathematical equation designed to evaluate the potential risk of a boat capsizing under certain conditions. It’s a valuable tool that takes into account a range of factors related to a boat’s design and characteristics, all of which contribute to its overall stability on the water. By using this formula, boaters can gain insights into how susceptible a boat might be to capsizing, helping them make informed decisions about their waterborne activities.

The formula’s components include measurements of a boat’s beam (width), displacement (weight), and the vertical center of gravity. Additionally, the formula considers the boat’s form stability – how its shape influences stability – and the weight distribution of passengers, cargo, and other items on board. The capsize screening formula offers a standardized way to assess a boat’s stability potential, making it an invaluable asset for boating safety. In the upcoming sections, we’ll delve into the individual components of the formula and their significance.

Components of the Capsize Screening Formula

The capsize screening formula takes into account several key components that collectively influence a boat’s stability. Understanding these components is essential for comprehending how the formula assesses the risk of capsizing. Here’s a breakdown of the crucial elements:

• Beam (B) : The beam refers to the width of the boat, measured from side to side. A wider beam generally contributes to greater initial stability by providing a wider base. However, extreme width can also lead to decreased stability if not balanced with other factors.
• Displacement (D) : Displacement represents the weight of the boat, including its hull, equipment, passengers, and cargo. A heavier boat tends to be more stable because it resists tipping over, but excessive weight can compromise stability if not properly managed.
• Metacentric Height (GM) : The metacentric height is a measurement of the boat’s stability relative to its center of gravity. It represents the vertical distance between the center of gravity (G) and the metacenter (M), which is the point where the buoyant force acts. A higher GM value contributes to greater stability, as the boat is more likely to return to an upright position after a disturbance.

The interaction of these components determines a boat’s overall stability. A wider beam, higher displacement, and sufficient metacentric height contribute positively to stability. However, a balance must be struck between these factors to ensure optimal stability without compromising other aspects of boat performance. The capsize screening formula evaluates these components to provide a quantitative measure of a boat’s vulnerability to capsizing.

How the Formula Works

The capsize screening formula is a straightforward mathematical equation that quantifies a boat’s susceptibility to capsizing based on its dimensions and characteristics. The formula is as follows:

Capsize Screening Formula: GM/B ≤ 2.0

Here’s how to interpret and apply the formula:

• Calculate Metacentric Height (GM) : Subtract the center of gravity (G) height from the metacenter (M) height. This results in the metacentric height (GM), which represents the boat’s stability. A higher GM indicates better stability.
• Determine Beam (B) : Measure the width of the boat, known as the beam (B), in feet.
• Calculate GM/B Ratio : Divide the calculated metacentric height (GM) by the beam (B) of the boat.
• Compare to 2.0 : The resulting GM/B ratio is then compared to the value of 2.0. If GM/B is equal to or less than 2.0, the boat is considered stable within the parameters of the formula. If the ratio exceeds 2.0, the boat may have reduced stability and a higher risk of capsizing.

Interpreting the Result:

• GM/B ≤ 2.0: The boat is considered to have adequate stability based on the capsize screening formula.
• GM/B > 2.0: The boat may have reduced stability, and caution should be exercised, especially in adverse conditions.

It’s important to note that while the capsize screening formula provides a useful guideline, other factors such as hull design, weight distribution, and handling characteristics also influence a boat’s stability. Therefore, while the formula offers valuable insights, it’s not the sole determinant of a boat’s overall stability.

Capsize Screening Numbers

The capsize screening formula yields a numerical value known as the GM/B ratio, which serves as an indicator of a boat’s stability. Understanding the range of capsize screening numbers is essential for assessing a boat’s vulnerability to capsizing:

• GM/B ≤ 2.0 : A boat with a GM/B ratio equal to or less than 2.0 is considered stable based on the capsize screening formula. This indicates that the boat’s metacentric height (GM) is adequately balanced in relation to its beam (B), contributing to its stability.
• GM/B > 2.0 : If the GM/B ratio exceeds 2.0, the boat may have reduced stability, potentially leading to a higher risk of capsizing. A GM/B value above 2.0 suggests that the metacentric height (GM) is not as well-proportioned to the boat’s beam (B), which can negatively impact stability.

The significance of lower numbers indicating higher stability lies in the relationship between the metacentric height (GM) and the beam (B) of the boat. A smaller GM/B ratio suggests that the metacenter is located relatively higher above the center of gravity, promoting better stability by resisting tipping forces.

Boat designers and naval architects aim to achieve a balanced GM/B ratio that falls within the acceptable range for the boat’s intended use. However, it’s important to remember that while the capsize screening formula provides valuable insights, other factors such as hull shape, weight distribution, and handling characteristics also contribute to a boat’s overall stability.

While the capsize screening formula provides a valuable tool for assessing stability, there are additional factors beyond the formula that can significantly influence a boat’s stability. These factors should be considered to ensure safe boating experiences:

• Weight Distribution : The distribution of weight within a boat plays a crucial role in its stability. Uneven weight distribution, especially in smaller boats, can lead to imbalances that affect stability. Properly distributing passengers, gear, and equipment according to manufacturer recommendations is essential.
• Loading : Overloading a boat with excessive weight can lower its stability and increase the risk of capsizing. Boats have maximum weight capacities specified by the manufacturer. Exceeding these limits can compromise stability and safety.
• Modifications : Alterations to a boat’s design, structure, or equipment can impact stability. Modifications should be made with careful consideration of their potential effects on weight distribution and overall balance. Unauthorized modifications can compromise the boat’s stability and structural integrity.
• Freeboard and Buoyancy : The freeboard—the distance between the waterline and the upper deck—plays a role in a boat’s ability to resist capsizing. Boats with lower freeboard may be more susceptible to swamping, reducing stability. The buoyancy of the hull design also influences stability and the boat’s ability to handle waves.
• Manufacturer Recommendations : Manufacturers provide guidelines for proper loading, weight distribution, and maximum capacities. Following these recommendations is crucial for maintaining the boat’s intended stability and safety.
• Weather and Water Conditions : External factors like wind, waves, and current can impact a boat’s stability. Larger waves and rough waters increase the likelihood of capsizing, particularly if the boat’s stability is already compromised.
• Skill and Experience : The operator’s skill and experience in handling the boat also play a role in maintaining stability. Proper boating techniques, such as adjusting speed in adverse conditions, can help mitigate stability risks.

Ultimately, a combination of factors contributes to a boat’s stability, and understanding how they interact is essential for safe boating. While the capsize screening formula provides a starting point, boaters should also be attentive to weight distribution, loading, modifications, and other relevant considerations to ensure optimal stability and minimize the risk of capsizing.

Significance of the Capsize Screening Formula for Boating Safety

The capsize screening formula holds immense significance in ensuring boating safety by providing boaters with a valuable tool to assess and understand a boat’s stability characteristics. Here’s why the formula matters for safe boating:

• Informed Boat Selection : When choosing a boat, understanding its stability is crucial. By calculating and comparing capsize screening numbers, boaters can make informed decisions that align with their intended use. Boats with lower capsize screening numbers are generally more stable, making them better suited for a variety of conditions.
• Matching Conditions : Different boating conditions require different levels of stability. Using the capsize screening formula allows boaters to match the boat’s stability with the conditions they plan to navigate, ensuring a safer and more comfortable experience.
• Awareness of Limits : Knowing a boat’s capsize screening number raises awareness of its stability limits. Boaters can avoid overloading the boat, staying within recommended weight capacities, and maintaining proper weight distribution to prevent stability issues.
• Safe Navigation : Understanding a boat’s stability characteristics enables boaters to navigate confidently in varying conditions. It helps them anticipate how the boat will respond to waves, wind, and maneuvers, reducing the risk of sudden instability and capsizing.
• Preventing Capsizing : The formula’s application aids in preventing capsizing incidents by identifying potential risks in advance. Boaters can take appropriate measures to mitigate stability concerns, such as adjusting loading, changing course, or slowing down.
• Education and Awareness : Learning about the capsize screening formula encourages boaters to deepen their understanding of boat stability principles. This increased awareness fosters responsible boating practices and encourages adherence to safe loading and operating procedures.
• Minimizing Accidents : By incorporating stability considerations into their boating plans, boaters can help minimize accidents, improve onboard safety, and protect both themselves and their passengers.

Incorporating the capsize screening formula into boating practices enhances safety and responsible seamanship. It empowers boaters to make well-informed decisions about boat selection, loading, and navigation, contributing to safer and more enjoyable experiences on the water.

Limitations of the Capsize Screening Formula

While the capsize screening formula serves as a valuable tool for assessing boat stability, it’s important to recognize its limitations. Boaters should be aware of these limitations and complement the formula’s insights with practical experience and prudent boating practices. Here are some key limitations to consider:

• Simplified Model : The capsize screening formula is a simplified mathematical model that doesn’t account for all the complex factors that influence a boat’s stability. Real-world conditions, such as wind, waves, and currents, can interact in ways that the formula doesn’t fully capture.
• Static Analysis : The formula provides a static analysis of stability based on a boat’s specifications at rest. It doesn’t consider dynamic factors like how the boat’s stability changes when underway, during turns, or when encountering waves.
• Weight Distribution : The formula assumes an even weight distribution across the boat’s length. In reality, uneven weight distribution, such as passengers moving around, can significantly impact stability.
• Experience Matters : While the formula is a helpful starting point, experienced boaters understand that stability is influenced by a combination of factors. Practical knowledge gained through time on the water is essential for reading conditions, making real-time adjustments, and responding to changing situations.
• Prudent Practices : Even if a boat’s capsize screening number indicates acceptable stability, boaters should still exercise caution and adhere to prudent practices. Avoid overloading the boat, maintain proper weight distribution, and adjust speed and course in response to changing conditions.
• Boater Skill : The formula doesn’t account for the skills and experience of the operator. A skilled boater who understands how to handle a boat in different conditions can enhance stability through proper maneuvering.
• Custom Boats : Custom modifications to a boat can alter its stability characteristics beyond what the formula predicts. Any modifications should be carefully considered, and their impact on stability should be understood.

While the capsize screening formula provides a valuable framework for assessing stability, it’s not a substitute for sound judgment, experience, and responsible boating practices. Boaters should use the formula as a starting point for understanding stability but also rely on their own expertise to make informed decisions on the water.

Resources and Calculators

For boaters interested in assessing their boat’s stability using the capsize screening formula, there are several online resources and calculators available that provide convenient tools for this purpose. These resources can help you quickly determine your boat’s capsize screening number and better understand its stability characteristics. Here are a few websites and tools to consider:

• Boat Stability Calculator : Various boating organizations and websites offer boat stability calculators that allow you to input your boat’s specifications, such as beam, displacement, and metacentric height. These calculators will then provide you with the capsize screening number and help you interpret its implications.
• Manufacturer Websites : Some boat manufacturers provide calculators or guidelines on their websites to help boaters assess their boat’s stability. These resources are often tailored to the specific models they offer.
• Boating Forums : Online boating communities and forums can be excellent sources of information. Fellow boaters may share their experiences, insights, and even tools they have used to calculate capsize screening numbers.
• Boating Safety Organizations : Organizations dedicated to boating safety often provide educational resources and tools related to boat stability. These resources can offer valuable insights into how to use the capsize screening formula effectively.
• Boat Design Software : Certain boat design software applications or programs include stability calculation features. These tools are particularly useful for boat designers, but they can also be used by boaters to assess the stability of existing boats.

When using online calculators and resources, be sure to input accurate and up-to-date information about your boat’s specifications. Remember that the capsize screening formula is a helpful starting point, but it’s not a substitute for careful consideration, boating experience, and responsible operation. Using these resources in conjunction with your own boating knowledge will contribute to a safer and more enjoyable boating experience.

Watch 12 things to check before going offshore | Video

Top 5 FAQs and answers related to capsize screening formula

What is the capsize screening formula .

The capsize screening formula is a mathematical equation used to assess a boat’s vulnerability to capsizing. It takes into account factors such as the boat’s beam (width), displacement (weight), and metacentric height (GM) to determine its stability characteristics.

How do I calculate the capsize screening number? 

The formula is: Capsize Screening Number = Beam / (Displacement / 64)^(1/3). You can find the boat’s beam and displacement in its specifications. Plug these values into the formula to calculate the capsize screening number, which indicates the boat’s stability.

What do different capsize screening numbers mean? 

Lower capsize screening numbers indicate higher stability. A lower number suggests that a boat is less likely to capsize. Higher numbers imply reduced stability, and boats with higher numbers might be less suitable for certain conditions.

Can I solely rely on the capsize screening number to assess a boat’s stability? 

While the capsize screening formula is a useful tool, it doesn’t account for all real-world scenarios. Factors like weight distribution, loading, modifications, and sea conditions can influence a boat’s stability. It’s important to consider these factors along with the capsize screening number.

Where can I find resources to calculate the capsize screening number?

There are various online resources and calculators available on boating websites, manufacturer websites, boating forums, and even boat design software. These tools allow you to input your boat’s specifications to calculate the capsize screening number. However, remember that these tools provide a starting point, and prudent boating practices and experience are essential for safe navigation.

In conclusion, the capsize screening formula serves as a valuable tool in assessing a boat’s stability, offering insights into its vulnerability to capsizing. By considering factors such as beam, displacement, and metacentric height, boaters can gain a clearer understanding of their vessel’s stability characteristics. This knowledge aids in making informed decisions about boat selection and operation, ultimately contributing to a safer and more enjoyable boating experience.

While the formula provides essential insights, it’s important to remember its limitations. Real-world conditions, weight distribution, and other variables can influence stability beyond the formula’s scope. As boaters, relying on experience, prudent practices, and manufacturer guidelines is equally crucial.

By utilizing online calculators and resources, boaters can easily apply the capsize screening formula to their vessels and gain valuable insights into their stability profiles. With this knowledge in hand, boaters can navigate the waters with confidence, prioritizing safety and enhancing their enjoyment on every journey.

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Sail Calculator

Go Directly To The Sail Calculator Here

What Carl’s Sail Calculator Does:

Physicist and sailor Carl Adler developed this online Sail Calculator for comparing sailboats  and its database has grown over a number of years to almost 3000 boats. It should be one of the first places you go on the Web if you want to know the vital statistics about a sailboat, including Length Overall (LOA) , Length on the Waterline (LWL) , Displacement and Sail Area .

The Sail Calculator will also give you valuable performance numbers for any vessel in its database or any numbers you enter, including the Displacement / LWL ratio, Theoretical Limiting Hull Speed, Sail Area / Displacement ratio, Length to Beam ratio, Motion Comfort value, Capsize Screening value, sailing category and Pounds per inch immersion value .

Naval architects use these values when they design a new boat, and from them you can determine a conventional displacement hull boat’s purpose and predict its performance. Note that planing hulls, catamarans and hydrofoil vessels are not defined in the same way. Here’s what the performance numbers mean:

Displacement/LWL ratio – Heavy boats (D/L above about 300) will carry big loads but require plenty of power to drive. Light boats (D/L below about 150) are generally quicker and more responsive but are affected by loading. Most boats have moderate displacement and they compromise the conflicting virtues of the extreme designs. Contemporary racing boats often have D/L ratios well below 100.

Hull Speed – A conventional hull, which moves through the water rather than rising atop it and planing across the surface, is limited in speed by length of the waves it produces; long waves travel faster. This wave length can be calculated and the top speed of the hull predicted. Long boats make long waves.

Sail Area / Displacement ratio – The SA/D ratio is like the power/weight ratio of an automobile. A high SA/D ratio (> about 18) indicates a powerful rig, while a low ratio indicates a more docile boat.

Length / Beam ratio – A long, narrow hull with limited interior space is easier to drive than a short, fat one with plentiful capacity. Compare L/B ratios to gain insight into the purpose of the boat.

Motion Comfort value – Not as widely used as the previous numbers, the Motion Comfort value tries to predict whether a boat has a quick, motion through the waves or a slow, easy motion. Note that some people get more seasick with a slowly rolling motion than a quick, jerky one. Your mileage will vary.

Capsize Screening number – Developed after the Fastnet Race tragedy, the Capsize Screening number is a quick way to judge if a boat is seaworthy. Values below 2.0 are desirable for offshore yachts. Do not put too much faith in the exact number, as it is an approximation only.

Pounds / square inch Immersion – When you load a boat, it sinks deeper into the water. This Immersion value indicates the weight carrying capacity of a vessel.

There is also a Prop Sizing section which will calculate the optimum propeller to use on any displacement-hull boat, based on noted naval architect Dave Gerr’s formulas.

 To The Sail Calculator

19 Comments on “ Sail Calculator ”

I corrected it. Thanks!

S2 7.3 specs from factory brochure (visible at boatbrochure DOT com SLASH products SLASH s2-7-3-meter-brochure the free preview is pretty legible)

LWL is 18.5 not 18.73 Beam is 8.0 not 8.5 Displ is 3250 not 3373 S.A. is 255, not 261

Thank you so much for your work maintaining this web page; it is tremendously valuable resource that I refer to often!

Tom, The Colgate 26 has a sail area different from that published on your calculator. It’s listed as 338 SF per https://www.colgate26.com/specifications/

Chris, Thanks for the note; I’m glad you find the Sail Calculator useful. I’ll change the value on the database on the next update, since your source is probably more accurate. I rarely know what the sources are when a user submits data, so there are definitely errors in there. It’s possible that one of the numbers is based on the 100% foretriangle measurement and the other is with a larger jib, which could be either the working jib or a Genoa. I get this question from time to time and probably should add something to the description about it (www.tomdove/blog/sail-calculator/). –Tom

Hi Tom, thanks for Carl’s calculator alive. I have a Tayana 48 DS and from their website, I get a different sail area. 1316 sq ft vs 1048.

Regards, Chris

Hi Tom, Looking at your specs the Marieholm 26 literature does not match what is posted. There were 3 versions of this boat built with the Marieholm being the middle one. The Folkboat website shows this: loa 25.83, lwl 19.83, beam 7.17, s.a. 280 sq. ft., draft 4′, disp. 4740, ballast 2750. The 1st model was built from wood, the last (3rd) model is called the Nordic Folkboat built from fiberglas but made with lapstrack design to look like wood. It was heavier in weight than the other 2 with less s.a.. Google “Folkboats Around the World” and the info is there on the main page. Hope this helps. Like to see values once new info is inserted. Wish I could figure it myself but not sure how to. Thank you, Sam

Thanks for catching that. I’ll correct it on the next update. — Tom

The Goletta Oceanica De Biot 39 is missing a decimal point in the LWL so it is throwing off all of the calculations.

David, There’s no simple answer to that. If you enjoy sailing the boat, it’s a good one. When you put the numbers into SailCalculator, it will return some basic information that can be very useful, but note that small, lightweight boats like the American 23 are sensitive to loading. The working displacement is actually the “Light Ship” displacement plus the weight of the average crew. Try adding the weights of you and your crew in SailCalculator and see how that affects the performance numbers. The people I have known who have the American 23 like it. It looks like a nice, stable daysailer. Enjoy! — Tom

I have American sailboat 23 ft. sailboat with a displacement 3500 lbs my keel is a 1000 lbs with a beam 7ft and 11 inch just wondering how good is this boat for sailing thanks

Mark, Very interesting. I can see why the Length/Beam ratio at the waterline would be the defining characteristic for hull speed. That can be an evasive number, I think. Multis with very narrow hulls will sink deeper into the water quickly as the boat is loaded, so the LWL/BWL could change dramatically. It seems that you’d have to be careful about specifying the displacement that produces a specific LWL/BWL ratio, don’t you think? Is there an issue of one hull being submerged more than the other when the boat is under sail? This seems especially important in trimarans, which often have one hull flying and the other deeply submerged, but a long, narrow cat would have some of the same response to a breeze. Keep me posted on your thoughts. I think you’ve hit on a key element here. — Tom

Hello, I’m a mechanical engineer and experienced multihull sailor that has long thought multihulls need a better performance parameter for comparison so sales guys can’t hoodwink people! I have some graduate school education from Dr. Marshall Tulin (UCSB) who has published many works regarding high-speed displacement mode for long slender hulls for naval/military applications and I think this work is very applicable to sailing multihulls. The critical parameter as far as hull drag for catamarans is really L/B at the waterline since other parameters as far as hull form go (prismatic coefficient) are generally within a narrow range. It has the benefit of implying displacement and waterline length as well, since a heavy boat must be either fat, or long to carry the displacement. As a result, I’ve been working on a parameter that includes both sail area and L/B at the waterline for performance comparisons. The trouble is Schionning is one of the few designers that cites L/B in all of his designs but it would be an easy measurement to take dockside, when the true displacement isn’t known.

Steve, I’ve never seen that formula but would love to have it. The speed of a multihull is largely a factor of the hull shapes, and most multis are not limited by the “Displacement Hull Speed” that determines the maximum speed of most monohulls. The hulls are generally long and narrow and do not create the speed-limiting waves. There are exceptions, and I think any formula that predicts the speed of a cat or tri would have to incorporate prismatic coefficient (“sharpness”). Most boats are not speed-limited by their sail area.

I’m looking for a formula that predicts potential performance of a cruising catamaran, in teh same way that SA/D does for monohulls. I saw teh formula years ago – it uses sail area and the second power (i.e., the square) of a factor, but I don’t recall anything else. Can you help me? -Steve

Charlie, Thank you for the compliment. I enjoy running the site and meeting so many people who love sailing. Good luck on your boat search; there are many good deals on used, mid-size cruising boats available now in the U.S. because builders flooded the market with 40-footers a few years ago. Now that so many Baby Boomers have finished their lifetime sailing adventures, the boats are for sale.

I’ve just been introduced to your site by a good friend from the US. Im looking for a retirement live aboard that can take me around the world. He gave me a potted history and speaks very highly of Carl Alder in this site in general. What a great tool. I’ll be flying to the states to view some boats that otherwise wouldn’t have even been on my Radar. Thank you Tom, Thank you Carl (Thank you Harvey).

Thanks for keeping Carl’s program alive, Tom. I sent him hundreds of small boat specs over the years and found quite a few errors from other inputs that Carl tried to correct. Between his poor vision, a lot of incorrect input (especially the difference between LOD versus LOA for most people) and the vague info from boat builders it was a long process. People should have supported him with far more donations, he was a good guy. Les Hall, San Antonio

Thanks for catching that, Paul. Yes, that would be a mighty powerful boat. It appears that the displacement should have been 14,500, so I corrected that. The SA/D ratio still looks a bit high, but I don’t know what the submitter used as a source. Enjoy the site and please send any other corrections you see. — Tom

Cavalier 37, LWL=30, Sail Area to Displacement=2314.05 Cant possibly be correct Great calculator, thanks for keeping it available. Cheers

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Capsize – how it happens

Posted by John Vigor | Sailing Tips

Planning for an unplanned inversion

Capsize: how it happens, and what you can do to survive it.

When Isabelle Autissier’s 60-foot racer capsized in the Southern Ocean, it sent a chill of fear through the sailing community. Sailors don’t like to think of capsize. But here was a big, well-found boat, a Finot-designed Open 60 Class flier, wallowing upside down in huge frigid swells, with her long thin keel jutting toward heaven. It was a bizarre and frightening sight.

Autissier was lucky. She was taking part in the Around Alone race, so her million-dollar boat was equipped with emergency satellite transmitters, position recorders, and lots of other equipment that no normal cruiser is likely to be able to afford or fit on board. She was eventually rescued in a wonderful feat of seamanship by Giovanni Soldini, a fellow competitor.

So what went wrong? And could it happen to you? It depends where you sail, but if you sail out of sight of land, whether at sea or on a lake, the answer is yes, it could. And you should always be prepared for it to happen. The good news is that most yachts of classic proportions will survive a capsize. Unlike Autissier’s extreme design, they will right themselves, although some might take longer than others.

You can form a crude idea of what went wrong with Autissier’s boat by imagining a long plank floating in the water. It doesn’t care which side is up. It’s happy floating either way up. That’s Autissier’s boat. Now imagine a plank with a heavy weight attached along one side, so the plank floats on edge. If you turn it upside down, the ballast quickly pulls it back again. That’s your normal yacht design. Autissier’s racer was shaped too much like a wide plank – too beamy and too light to recover from an inverted position, despite the long heavy keel. It’s one of the paradoxes of naval architecture that an excessively beamy boat, while hard to capsize in the first place, is unseaworthy if she is inverted.

Furthermore, a light, shallow, beamy boat capsizes more easily than a narrow, deep, heavy boat because she offers the seas more leverage to do their work, and because she is quicker to respond to the upward surge of a large swell.

Planing hulls

Designers create racing boats like Autissier’s because that shape gives them the ability to plane at high speeds. In other words, they deliberately sacrifice seaworthiness on the altar of speed, and the boats rely on the skill of their crews to keep them upright. Unfortunately, singlehanders have to sleep now and then, so they can’t be on watch all the time.

While it’s true that a good big boat is less likely to capsize than a good small boat, there is no guarantee that even the largest yachts are immune from capsize. It’s not the wind that’s the problem. It’s the waves.

Tests carried out at Southampton University in England have shown that almost any boat can be turned turtle by a breaking wave with a height equal to 55 percent of the boat’s overall length. Even if you don’t like to think about it, you know in your heart that it’s a reasonable finding. It means your 35-footer could be capsized through 180 degrees by a 20-foot wave. Even a 12-foot breaking wave would roll her 130 degrees from upright – from which position she may turn turtle anyhow.

And if you imagine you’re never going to encounter a 20-foot wave, think again. Waves of that size can be generated in open water by a 40-knot wind blowing for 40 hours. And a 12-foot wave is the result of a 24-knot wind blowing for 24 hours. Plenty of those around.

Large waves are formed in other ways, too. A current flowing against the wind will create seas that are much larger and steeper than normal. And the old stories about every seventh wave being bigger than the rest have a basis of truth, although it’s not necessarily the seventh wave. It could be the fifth or the ninth. The point is that wave trains occasionally fall in step with each other at random intervals, literally riding on one another’s backs, to form an exceptionally high wave. We call that a freak wave, but it’s actually more normal than we care to admit.

Bigger waves

Scientists calculate that one wave in every 23 is more than twice as high as the average. One in 1,175 is three times bigger. And one in 300,000 is four times the average height. They may be far apart, but they’re out there, and many big ships have been lost to them.

John Lacey, a British naval architect, put forward an interesting proposition after the 1979 Fastnet Race, in which 63 yachts experienced at least one knock-down that went farther than 90 degrees and remained upside down for significant periods.

He explained that the old International Offshore Rule for racers had radically changed the shape of yacht hulls by greatly increasing the proportion of beam to length, which gave them more power to carry sail without the need for additional ballast. It also gave them more room below, of course.

But the flatiron shape of the hull made it very stable when it was inverted. To bring the boat upright again would require about half the energy needed to capsize the yacht in the first place, Lacey calculated.

“Since the initial capsize may have been caused by a once-in-a-lifetime freak wave, one could be waiting a long time for a wave big enough to overcome this inverted stability,” he commented. Autissier’s experience bore out that prophetic statement. Her boat was still upside down when she abandoned it.

Lacey did some more sums and figured that a narrower cruising hull with a lower center of gravity than a typical IOR boat would require only one-tenth of the capsize energy to recover from a 180-degree capsize.

“It therefore seems, in my opinion, that we should tackle the problem from the other end, and design yachts for minimum stability when upside down,” he concluded.

Deep-vee cabin

His recommendation is not likely to be taken too seriously, but he certainly does have a point. You could make an inverted yacht unstable with narrow beam, a very deep keel with a lot of weight at the very end of it for righting leverage, and a deep-vee cabintop, or at least one that was narrow on top and broad at deck level. For the same reason, flush-decked yachts should be avoided, because they’re likely to be much more stable upside down.

But as in everything to do with sailboats, there are compromises to be made. Deep narrow hulls might recover quickly from inversion, but as sailors discovered a century ago when they were all the rage, they’re lacking in buoyancy. They’re also wet, and they have very little accommodation.

Two basic design features probably govern the probability of capsize more than any others. The first is inertia and the second is the shape of the keel.

Inertia is not generally well understood, but it’s the first line of defense against a wave impact. In simple terms, inertia is resistance to change. The inertia of a moving boat works to keep her moving on course, even though other forces are trying to halt or divert her. The inertia of a boat at rest resists any sudden attempt to start her moving.

Obviously, because inertia varies with mass, a heavy boat has more inertia than a light boat, so a wave hitting her from the side is going to get a slower response. Light-displacement boats are more likely than heavy boats to be picked up and hurled over by a plunging breaker.

Narrow beam is a help, too, because the force of a breaking wave is concentrated nearer the centerline of the yacht, where it has less overturning leverage.

Spreading weight

The way weight is distributed on a boat also affects its inertia. A wide boat with a light mast and a shallow keel will respond very quickly to every wave with a lively, jerky motion. A boat with a heavier mast and a deeper keel has its weight spread out over a greater span, and it’s more difficult to change its speed or direction, so the force of a breaking wave may be dissipated before it has a chance to overturn the boat. Inertia, incidentally, is what keeps a tightrope walker aloft. It’s contained in that long stick. If you push down on one side of it suddenly to regain your balance, it almost bounces back at you. It will subsequently move slowly away, but you can recover it with a long gentle pull as you lean the other way.

A long, old-fashioned keel resists sudden rolling simply because it’s difficult to move anything that big sideways through the water. A fin keel, with its meager surface area, is much more easily moved when it’s stalled; thus, the boat to which it’s attached is more easily overturned. But a fin keel that’s moving through the water acquires much more stability, which is why fin keelers should be kept moving in heavy weather.

Capsize screening formula

The maximum beam divided by the cube root of the displacement in cubic feet, or Maximum beam (feet) = less than 2 3÷Displ/64 The displacement in cubic feet can be found by dividing the displacement in pounds by 64. The boat is suitable for offshore passages if the result of the calculation is 2.0 or less, but the lower the better.

Although there are design factors that improve seaworthiness (usually at the expense of speed and accommodation), and although there are tactics you can use in a storm to minimize the chances of overturning, no boat is totally capsize-proof. That is not to say that every boat is going to capsize, of course, even the ones most likely to. After all, hundreds of yachts cross oceans every year without mishap. But prudent sailors keep the possibility in mind and do what they can to forestall any problems and to lessen any damage resulting from an inversion.

Large forces

If you have never given any thought to inversion, the results of a capsize can be devastating, not only on deck but down below as well. Not many people realize what large forces are involved in a capsize, especially the head-over-heels capsize called a pitchpole. It’s not just a gentle rolling motion. The contents of lockers and drawers can be flung long distances in the saloon, and you could easily find yourself standing in a state of disorientation on the overhead in a seething mess of battery acid, salt water, clothing, ketchup, mayonnaise, diesel fuel, paint thinner, knives, forks, and shards of broken glass. There will be no fresh air entering the cabin to dissipate the fumes. And it will be dark because your ports will be under water.

So, first things first: presuming you haven’t been injured by flying objects, can you lay hands on flashlights? Were they stored safely in a special place that you can reach without having to shift a wodge of soaked bunk mattresses? Is there one for every member of the crew? Are the batteries fresh? You may not stay upside down for long. But if you’re unlucky, like Isabelle Autissier, you will find you need a flashlight more than anything else on earth.

There are some other things you should think about before you ever set sail. And there are some precautions you can take.

Avoiding capsize

• Avoid heavy weather. “The most dangerous thing on a boat is an inflexible schedule.” Thanks to Tony Ouwehand for this observation.
• Avoid taking large waves abeam, particularly breaking waves.

Heave to. Run (down wave) using a drogue to keep speed down to 3 to 5 knots. Use a sea anchor from the bow or a series drogue from the stern. (Practice rigging and deploying these in moderate conditions.)

• Is your rig as strong as possible? Will it withstand the tremendous forces of a capsize?
• Do you have a plan to free a toppled mast from alongside, where it can batter holes in your hull? Have you ever thought how difficult it would be to cut the rigging, even with a decent pair of bolt cutters, on a slippery deck that’s suddenly rolling viciously?
• Do you have material on board for a jury rig? Have you thought about how you would use it?
• Will your radio transmitter’s antenna come down with the rig? Do you have a spare?
• Will your EPIRB start working automatically because it’s been under water – whether you want it to or not?

The cockpit

• Are your cockpit lockers waterproof? Can you imagine how quickly you’d sink if one of them was open at the time of capsize?
• Do your companionway hatchboards lock in position? Have you ever thought how much water would get below if one or more fell out as you turned over?
• What have you done about waterproofing the cowl vents for the engine? Those are huge holes in what would become the bottom of the boat. (The same goes for Dorade boxes, incidentally. Each one is a potential three- or four-inch hole in the bottom. Fit them with deck plates for sea work, on deck and down below.)
• If you’re in the cockpit when the boat capsizes, will you be attached by a harness? Will you be able to free yourself if you’re trapped under water and the boat stays inverted for some time?

The anchor locker

• If the anchors and chain are not fastened down securely they could bash their way through the locker lid and cause all kinds of havoc.
• Is your self-draining deck anchor locker waterproof? Many aren’t completely sealed at the top, where wires for pulpit-mounted running lights come though, and would let in water.

The engine room

• Is your engine mounted securely enough to withstand a capsize? I know of one boat in which the engine was hurled from its mounts during a pitchpole, causing great destruction.
• What if the engine’s running during a capsize? Could you switch it off quickly, with everything upside down? Would the oil run out? Would the fuel drip out of the tanks? Are your breathers inside or outside?
• Are the batteries fastened down firmly enough? Can you imagine what damage they could do if they got loose? And will they drip acid if they’re upside down? (Newer batteries – gel cells and AGMs will not spill acid when inverted. -Ed.)
• Can you turn the stove off? If there’s a smell of gas, can you deal with it? Have you made sure the galley cupboards can’t fly open during a capsize and turn the saloon into a sea of broken glass and chip dip?
• Can you lay hands on a fire extinguisher quickly? It could save your life.
• Have you figured out a way to keep all those loose tops in place in the saloon – the boards that cover access to storage under bunks, the bilge boards, and so on? Some boats have inside ballast, and many have heavy objects, such as storm anchors, stowed in the bilges. Make sure they stay there, because if they get loose they can come crashing through the overhead (your new “floor”) and sink the boat very quickly.
• Make sure your bunk mattresses will stay in place, too, otherwise they will greatly hamper your attempts to get around.
• Have you figured out a way to pump bilge water out of an inverted boat? Think about it. It’s not easy.
• Most books could escape from their racks during a capsize and become potentially harmful flying objects. Have you solved that problem?

Important documents

• The ship’s papers and your own personal documents should be in a watertight container in a secure locker, one that is not too high up in the boat because that’s where the water will be when you capsize.

There are many other systems and pieces of gear on a boat that could be affected by a capsize. When you use them, think inverted. Imagine what would happen if they got loose. Invent ways to keep things in their places during an unplanned inversion. Don’t ever imagine it’s wasted work. It’s one of the unspoken rules of the sea that if you’re prepared, the worst is not likely to happen. If you’re not, you’re bound to attract trouble.

More on the subject

Tami Ashcraft wrote a compelling story of the realities of inversion and its aftermath in her book, Red Sky in Mourning: The True Story of a Woman’s Courage and Survival at Sea , reviewed in our May 2000 issue. John Vigor goes into more depth about preparation for capsize in his book, The Seaworthy Offshore Sailboat .

Article from Good Old Boat magazine, November/December 2000.

About The Author

John Vigor is a retired journalist and the author of 12 books about small boats, among them Things I Wish I’d Known Before I Started Sailing, which won the prestigious John Southam Award, and Small Boat to Freedom. A former editorial writer for the San Diego Union-Tribune, he’s also the former editor of Sea magazine and a former copy editor of Good Old Boat. A national sailing dinghy champion in South Africa’s International Mirror Class, he now lives in Bellingham, Washington. Find him at johnvigor.com.

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How Often Do Sailboats Capsize: A Comprehensive Guide

Table of Contents

Introduction

1. Understanding Sailboat Stability

Before we dive into the topic of sailboat capsizing, it’s essential to grasp the concept of sailboat stability. Sailboats rely on a delicate balance between buoyancy, the shape of their hulls, and the distribution of weight. This equilibrium ensures that the boat remains upright and maintains its stability while maneuvering through water.

2. Factors Contributing to Sailboat Capsizing

Several factors can contribute to sailboat capsizing. Understanding these factors will help sailors make informed decisions to minimize the risk of capsizing incidents.

Weather Conditions

Adverse weather conditions, such as strong winds, high waves, and sudden storms, pose a significant risk to sailboats. Powerful gusts can exert excessive force on the sails, causing the boat to tip over or capsize. It’s crucial for sailors to monitor weather forecasts and avoid venturing into hazardous conditions.

Design and Stability Characteristics

The design and stability characteristics of a sailboat play a crucial role in its resistance to capsizing. Factors such as hull shape, keel design, and ballast contribute to a boat’s stability. Sailboats with deep keels and a low center of gravity are generally more stable and less prone to capsizing.

Improper Handling and Operator Error

Inexperienced sailors or those who fail to adhere to proper handling techniques are at a higher risk of capsizing their sailboats. Incorrect sail trim, excessive heeling, abrupt maneuvers, or overloading the boat can destabilize the vessel, leading to a capsize. It is essential for sailors to receive proper training and practice good seamanship.

3. Statistics on Sailboat Capsizing

To gain a better understanding of the frequency of sailboat capsizing, let’s explore some relevant statistics.

Global Incident Rates

Accurate global incident rates for sailboat capsizing are challenging to determine due to underreporting and varying definitions of “capsizing.” However, it is evident that capsizing incidents occur across different bodies of water worldwide.

Types of Sailboats Most Prone to Capsizing

Certain types of sailboats are more susceptible to capsizing than others. Small, lightweight dinghies and high-performance racing sailboats are more likely to capsize due to their design and the nature of their intended use. Larger cruising sailboats with keels and more stability tend to have a lower risk of capsizing.

Capsizing Incidents and Fatalities

While the majority of sailboat capsizing incidents do not result in fatalities, it is crucial to prioritize safety and minimize the risks involved. Fatalities can occur in extreme weather conditions or when proper safety measures are not followed.

4. Preventive Measures and Safety Tips

To reduce the likelihood of sailboat capsizing and ensure a safe sailing experience, consider the following preventive measures and safety tips:

Checking Weather Conditions

Always check weather forecasts before setting sail. Avoid venturing into adverse weather conditions, such as high winds or storms. Stay informed and have a backup plan if conditions worsen unexpectedly.

Proper Boat Maintenance and Rigging

Regular maintenance of your sailboat is essential for its seaworthiness. Inspect the rigging, sails, and hull for any signs of wear or damage. Ensure that all components are properly rigged and in good working condition.

Adequate Training and Experience

Obtain adequate training and gain experience before setting out on the open water. Learn the basics of sailing, including boat handling, navigation, and understanding weather patterns. Consider taking sailing courses or joining a sailing club to enhance your skills.

Safety Equipment and Emergency Preparedness

Equip your sailboat with essential safety equipment, including life jackets, flares, a first aid kit, and a functioning VHF radio. Familiarize yourself with emergency procedures and ensure that everyone on board knows how to use the safety equipment.

Understanding Sailboat Limits and Operating within Them

Every sailboat has its limits. Understand the capabilities and limitations of your boat, especially regarding wind conditions and weight capacity. Avoid overloading the boat and be mindful of the sailboat’s stability characteristics.

5. Conclusion

Sailboat capsizing is a concern for sailors worldwide. However, with proper knowledge, preparation, and adherence to safety guidelines, the risk of capsizing incidents can be significantly reduced. Understanding sailboat stability, recognizing contributing factors, and implementing preventive measures will ensure a safer and more enjoyable sailing experience for all enthusiasts.

Frequently Asked Questions (FAQs)

1. is capsizing a common occurrence for sailboats.

Capsizing incidents are relatively rare, especially when considering the vast number of sailboats worldwide. However, it is crucial to prioritize safety and take measures to minimize the risk of capsizing.

2. Are smaller sailboats more likely to capsize?

Yes, smaller sailboats, such as dinghies, tend to be more prone to capsizing due to their lightweight construction and design characteristics. However, proper handling and adherence to safety guidelines can mitigate the risk.

3. Can a sailboat capsize in calm weather conditions?

While capsizing is more commonly associated with adverse weather conditions, it is possible for a sailboat to capsize even in calm weather. Improper handling or operator error can destabilize the boat, leading to a capsize.

4. What should I do if my sailboat capsizes?

If your sailboat capsizes, remain calm and follow proper safety procedures. Stay with the boat, as it provides flotation. Signal for help if needed and follow appropriate rescue techniques.

5. Are there any specialized courses for learning how to prevent sailboat capsizing?

Yes, there are various sailing courses available that focus on safety and preventing capsizing incidents. These courses cover topics such as seamanship, boat handling techniques, and understanding weather conditions.

In conclusion, understanding the factors contributing to sailboat capsizing, maintaining proper sailboat stability, and following preventive measures are key to enjoying a safe and adventurous sailing experience. While sailboat capsizing incidents may occur, they can be minimized through knowledge, experience, and preparedness. By checking weather conditions, maintaining the sailboat, receiving adequate training, equipping with safety gear, and understanding the boat’s limits, sailors can navigate the waters with confidence. Remember, safety should always be a top priority to ensure a memorable and incident-free sailing journey.

Mark Alexander Thompson

Mark Alexander Thompson is a seasoned sailor with over five years of experience in the boating and yachting industry. He is passionate about sailing and shares his knowledge and expertise through his articles on the sailing blog sailingbetter.com. In his free time, Mark enjoys exploring new waters and testing the limits of his sailing skills. With his in-depth understanding of the sport and commitment to improving the sailing experience for others, Mark is a valuable contributor to the sailing community.

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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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Assessing Stablity

One of the potentially more significant pieces of data available for assessing the suitability of a boat for voyaging is its stability curve (otherwise known as its GZ curve). A stability curve is developed by calculating or measuring the forces needed to heel a boat and then using accurate data describing the hull’s shape and center of gravity to develop a curve that shows, among other things, the point at which the boat has its maximum resistance to heeling (the point of maximum stability) and the point at which it will roll over and turn upside down (the limit of positive stability [LPS], also known as the angle of vanishing stability [AVS] and the point of no return).

Depending on how the calculations are made, it is possible to come up with significantly different numbers for the same boat. Unfortunately, the International Measurement System (IMS) and the International Standards Organization (ISO) have different methodologies, although both are based on a lightly loaded condition and both exclude the effect of any superstructure on the calculation, so the results are likely to be reasonably close. Much bigger differences are likely between either of these methodologies and any methodology that includes the superstructure (which significantly increases the LPS/AVS) and/or substantial payload. For this reason, it is important to use the same measurement methodology when comparing boats.

Given that the European community is requiring some sort of stability testing for all new boats, we can expect most boats (both European and American) to be tested to the ISO standard in the near future, which will provide a measure of consistency.

However, a couple of caveats need to be borne in mind. On one hand, this stability test is conducted in a lightly loaded condition (minimum sailing condition – factory installed equipment on board plus an estimated crew weight), which tends to understate the stability of a boat loaded down with voyaging stores.

On the other hand, the test is done on the honor system to some extent, so it is quite possible for a builder to test a boat with, for example, a deep-draft keel and hanked-on sails, which will maximize the stability rating, and then sell the boat with a shoal-draft keel and roller furling sails, which will significantly reduce its stability. As always, for accurate comparisons it is important to find out on what basis the numbers have been derived. Beam versus stability

Irrespective of the way in which the calculations are run, a beamy, lightweight boat that relies primarily on form stability for its stiffness will reach its point of maximum stability and its limit of positive stability well before a deeper-draft, narrower-beam boat that relies more on ballast weight for stiffness. If either boat capsizes, the beamy, lightweight boat will have a greater tendency to remain upside down, as is well illustrated by some of the current crop of single-handed, round-the-world racers, which are quite stable in the inverted position.

“The way beam is used in combination with displacement and center of gravity is the crux of the stability question,” wrote Olin Stephens, the famous yacht designer, in Desirable and Undesirable Characteristics of Offshore Yachts, edited by John Rousmaniere. “The worst of all combinations is large beam with a light-displacement, shoal-bodied hull having necessarily limited ballast that is too high.” These characteristics will be reflected in a low AVS number.

If a boat is intended for extended voyaging where it runs the risk of getting caught in extreme conditions, it should have an AVS of at least 120°; a number of experienced cruiser/writers recommend 130°. The figure of 120° is chosen because if such a boat is inverted, in theory, another wave will right it in about two minutes, which is the longest most people can hold their breath. With an AVS of 100°, the boat will theoretically remain inverted for five minutes; at 140° the inversion time is minimal. For coastal voyaging, an AVS as low as 115° is acceptable.

Our Pacific Seacraft 40 has not yet been measured under the IMS or ISO rules, but it has been measured with the superstructure and cockpit included in the calculations (a more realistic assessment). This produces a point of maximum stability of 65° and ·VS of 143°, both numbers being on the high end for modern boats. Although these numbers would be lower using the IMS and ISO methodologies, the AVS would still be well above 130°. Stability ratio

Another interesting way of comparing boats is to take the area under the positive portion of the stability curve, which represents the amount of energy necessary to capsize the boat, and divide this by the area under the negative part of the curve, which represents the energy required to return an inverted boat to the point at which it will right itself.

The ratio of these two areas – the stability ratio – is a measure of the relative stability of the boat, both upright and capsized. The higher the number, the better. On a voyaging boat, it should be at least 3.0, and preferably higher; the farther offshore the boat goes, the higher the ratio should be. I don’t have the ratio for the Pacific Seacraft 40, but my guess is it is above 10.0.

Stability curves and ratios are useful as a guide for selecting offshore boats, but they need to be put in perspective. The curves are based on a static calculation and take no account for the dynamic forces at work in conditions of heavy breaking seas when a knockdown is most likely to occur. According to one school of thought, a boat with relatively low freeboard and a deep keel has significantly less wave-loading area than one with high freeboard, and is therefore less likely to get rolled. According to another school of thought, a lightweight boat with high freeboard and a shallow keel is more likely to skid sideways before the wave, dissipating the wave’s energy and so forestalling a capsize!

As noted, the stability curve and ratio are usually based on some form of light ship displacement. The addition of voyaging stores and gear has a significant effect, since weight somewhat above or anywhere below the boat’s center of gravity tends to increase its stability; whereas, added weight well above the center of gravity decreases stability.

The higher the added weight on the boat, the more deleterious the effect. Such things as a radar antenna sited high on the mast, roller reefing headsails, an outboard motor stowed on the rail, and dinghies, anchors, ground tackle, and all the other gear commonly placed well above the waterline, all have a significant, negative impact on the numbers. We have all these things on our boat.

Peter Bruce, in the fifth edition of Adlard Coles’ Heavy Weather Sailing, reports that the addition of in-mast furling and a roller-reefing headsail to a 28.5-foot production voyaging yacht reduced its AVS/LPS from 127° to 96°. This is a potentially life-threatening reduction in stability. Although this is an extreme case (the reduction in AVS caused by similar gear on a larger boat of significantly heavier displacement is more likely to be on the order of 3 to 4 percent), voyaging sailors need to be aware of the effect that additional weight can have on stability, especially weight high up, and then make sure that any given boat can handle the load without a serious loss of performance or stability. Every effort must be made to keep heavy weights low in the boat. Capsize screening value andSTIX number

After the disastrous 1979 Fastnet race, in which numerous boats were repeatedly rolled and 15 people lost their lives, a long, hard look was taken at the stability issue. Many yacht designers acknowledged that the International Offshore Rule (IOR), which dominated yacht design in the 1970s and 80s, under which many of the participating boats were designed, was actually promoting the development of unsafe boats (non-IOR boats built before 1975 survived the race with few problems).

A great deal of work was put into developing a simple formula that would weed out the worst excesses resulting from attempts to beat the rule. The formula that was developed is known as the capsize screening formula. It is intended to assess both “the risk of being unduly, easily capsized and the risk of sticking in the inverted position for an extended period of time,” according to the Final Report of the Directors, USYRU/SNAME Joint Committee on Safety from Capsizing.

The capsize screening value for any boat is found by dividing the cube root of the boat’s displacement volume into its maximum beam (Bmax). The higher the resulting number is than a value of 2.0, the greater the chance that the boat will be unduly prone to capsize; if it is below 2.0, it should be safe offshore.

It should be noted, however, that since the capsize screening value is a function of displacement and beam, any two boats with the same displacement and beam will have the same capsize screening value. This is so even if, for example, one boat has a heavily ballasted, deep-fin keel, while the other has a centerboard and internal ballast, in which case the former will in fact be much more stable.

At press time, the ISO was working (and has been for eight years) on a more sophisticated stability index (STIX), which takes into account a greater number of variables. Until this work is completed, the existing capsize screening value, despite its shortcomings, is a useful indicator of stability.

Looking at our Pacific Seacraft 40: it has a half-load displacement of 26,830 lbs (light ship + 3,750 lbs), which is 419 cubic feet. The cube root of 419 is 7.48; Bmax is 12.42 feet. The capsize screening value is 12.42/7.48 = 1.66, which is well below the target of 2.0, confirming the boat’s high degree of capsize resistance. If we use the light ship displacement to work the numbers (this is the worst-case scenario in terms of the capsize screening value) we get a value of 1.75, which is still well below the target of 2.0.

Once the STIX standard is completed, it should provide a more comprehensive means of comparing boats than the current capsize screening value (although this is by no means certain – the standards-writing process is both political and controversial). However, earlier drafts of the STIX standard gave a score of 30 or more, which resulted in an A rating – the rating for oceangoing boats – to boats with an AVS as low as 95, in spite of the fact that these boats were clearly not suitable for extended ocean voyaging. After a well-publicized sinking in a Bay of Biscay gale of an A-rated boat with an AVS of 110, the STIX score for an A rating has been raised to 32, and there is discussion of raising the AVS to 120. Minimum numbers

Given these facts, and bearing in mind that longer boats inherently score higher on the STIX scale than shorter boats, regardless of the number that the STIX committee finally determines is appropriate for an A rating, it may make sense to set a minimum score of 35 for oceangoing voyaging, or maybe even 40, and to progressively raise this for boats more than 40 feet in length. For coastal voyaging, a minimum STIX number of 30 will give a greater degree of security than the current 23. It, too, should be increased for boats more than 40-feet in length.

A final word of caution is in order. Calculating a STIX number is a complicated (and hence, expensive) process. Boatbuilders have the option of entering worst-case default numbers into the formula at various points. Any builder who can do this and still come up with a STIX number that exceeds 32, and thus get a CE A rating, may well choose this route in order to keep down costs. But in this case, the resulting STIX number is likely to be well below what it would be if the full calculation were to be made. As with all numeric parameters, when comparing STIX numbers it is important to find out how they have been derived.

If the conditions get nasty enough, any boat can be rolled. At such a time, the survival of the crew is going to be significantly affected by how fast the boat will right itself. Only boats that are likely to recover in a minute or two should be considered for blue-water voyaging. With this in mind, I look for an AVS/LPS of 120 or higher, a capsize screening value of 2.0 or higher, and a STIX rating well above 32.

This article is an excerpt from Contributing Editor Nigel Calder’s latest book, Nigel Calder’s Cruising Handbook, published by International Marine/McGraw Hill.

By Ocean Navigator

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Sailboat Calculators

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The Sailboats Calculators below will enable you to calculate the main Sailboat Ratios, using data that you can retrieve from the Boat table or your own data.

We will be adding more calculators along the way and more in-depth explanations of how they work and what they can help you with., hopefully you will enjoy them and find them useful to search or understand the characteristics of your or any given sailboat ..

SA/D range of values

16 to 18 Heavy offshore cruisers 18 to 22 Medium cruisers 22 to 26 Inshore cruisers, racing boats 26 to 30+ Extreme racing boats

Ballast/Displacement:

A Ballast/Displacement ratio of 40 or more translates into a stiffer, more powerful boat that will be better able to stand up to the wind.

Displacement/Length:

The lower a boat’s Displacement/Length (LWL) ratio, the less power it takes to drive the boat to its nominal hull speed.

less than 100 = Ultralight;

100-200 = Light;

200-275 = Moderate;

275-350 = Heavy;

350+ = Ultraheavy;

Comfort Ratio:

This is a ratio created by Ted Brewer as a measure of motion comfort. It provides a reasonable comparison between yachts of similar size and type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Consider, though, that the typical summertime coastal cruiser will rarely encounter the wind and seas that an ocean going yacht will meet.

Numbers below 20 indicate a lightweight racing boat;

20 to 30 indicates a coastal cruiser;

30 to 40 indicates a moderate bluewater cruising boat;

40 to 50 indicates a heavy bluewater boat ;

over 50 indicates an extremely heavy bluewater boat.

Comfort ratio = D ÷ (.65 x (.7 LWL + .3 LOA) x Beam^1.33), where displacement is expressed in pounds, and length is expressed in feet.

Capsize Screening Formula (CSF):

Designed to determine if a boat has blue water capability. The CSF compares beam with displacement since excess beam contributes to capsize and heavy displacement reduces capsize vulnerability. The boat is better suited for ocean passages (vs coastal cruising) if the result of the calculation is 2.0 or less. The lower the better.

Hull Speed Calculator

Hull speed calculator is a simple calculator that determines a vessel’s hull speed based on the length of the vessel’s waterline.

Boat Speed Calculator

The boat speed calculator calculates the top speed of a boat based on the boat’s power and her displacement. If you try to understand how fast a boat can go, this calculator will help you answer that. The boat speed calculator utilizes a constant known as Crouch constant which differs based on the type of the boat.  

FOR MULTIHULLS ONLY:

Bn – bruce number:.

The Bruce Number is a power-to-weight ratio for relative speed potential for comparing two or more boats. It takes into consideration the displacement and sail area of main and jib. 100% fore-triangle only, no overlapping sails.

Chris White, “The Cruising Multihull”, (International Marine, Camden, Maine, 1997), states that a boat with a BN of less than 1.3 will be slow in light winds. A boat with a BN of 1.6 or greater is a boat that will be reefed often in offshore cruising.

Derek Harvey, “Multihulls for Cruising and Racing”, International Marine, Camden, Maine, 1991, states that a BN of 1 is generally accepted as the dividing line between so-called slow and fast multihulls.

BN = SA^0.5/(Disp. in pounds)^.333

Kelsall Sailing Performance (KSP):

Another measure of relative speed potential of a boat. It takes into consideration “reported” sail area, displacement and length at waterline. The higher the number the faster speed prediction for the boat. A cat with a number 0.6 is likely to sail 6kts in 10kts wind, a cat with a number of 0.7 is likely to sail at 7kts in 10kts wind.

KSP = (Lwl*SA÷D)^0.5*.05

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Sailboat Specifications 101: Explained For Beginners

As a newbie to sailing, the sailboat specifics can be overwhelming. Taking time to familiarize yourself with the measurements and vocabulary associated with boats will allow you to be more informed about boats and know which type is right for which activity. You’ll be a better sailor and boater with this knowledge.

Table of Contents

LOA – Length Overall

Length Overall (LOA) is the most common measurement used to describe the size of a sailboat. It refers to the total length of the vessel, from the tip of the bow (front) to the aft end of the stern (back).

LOA is typically measured in feet or meters. This measurement can be useful when comparing boats of similar types, as it gives you an idea of the overall size.

LOD-length on deck

LOD, or Length on Deck, is the measurement of the boat from the tip of the bow to the stern along the deck.

This length does not include any spars, bowsprits, antennas, etc. that are mounted above the main deck.

The difference between LOD and LOA (length overall) is that LOA takes into account any protrusions such as spars and bowsprits. LOD may be shorter than LOA sometimes.

LWL – Load Waterline Length

The LWL or Load Waterline Length is the measurement of the length of a boat at the point where it touches the water.

It is the length of the boat that makes contact with the water and is often shorter than the overall length (LOA) due to the curvature of the hull.

The LWL plays an important role in determining the performance of a sailboat; for example, a longer LWL can help increase stability and reduce drag, allowing the boat to move more efficiently through the water.

The LWL also affects the size of the sail area needed to power the boat. As such, boats with a longer LWL will require larger sails to generate adequate power, while boats with a shorter LWL may need smaller sails.

Beam – The width of the boat

The beam of a sailboat is the maximum width of the hull and is an important measurement for sailing performance.

A wider beam provides more stability on the water and increases the overall sail area. Having a larger sail area will help to increase speed and maneuverability in windy conditions.

It’s important to consider the beam of the boat when deciding what type of sails to use. A boat with a wider beam will require bigger sails, while a boat with a narrower beam will require smaller sails.

Draft – The depth of the boat in the water

Draft measures the distance from the waterline to the lowest point of the boat’s hull when it is fully loaded.

This is important because it affects the boat’s maneuverability, stability, and performance in different sea conditions.

It also affects the sail area of the boat, since a greater draft can provide more stability and lift, allowing for larger sails to be used. Shallow draft boats tend to be able to get into shallower waters than those with deeper drafts.

Full keel vs. modified keel vs. fin keel

The three main types of keels are full, modified, and fin keels.

Full keels are the oldest and most traditional type of keel. They are typically found on heavier displacement boats such as cruisers and larger sailboats.

Full keels provide more stability due to their size and weight, but also create more drag, which can slow down the boat.

Modified keels are a hybrid between full and fin keels. They are often used on boats with moderate displacement, meaning they have a moderate amount of weight.

Modified keels provide a good balance of stability and speed due to their shape and size.

Finally, fin keels are usually found on lighter displacement boats such as racing and performance sailboats.

Fin keels have the least amount of drag, allowing the boat to move faster, but they are not as stable as full or modified keels.

Displacement – The weight of the boat

The displacement of a boat refers to the total weight of the boat, including all of the materials used to construct it. It is usually measured in either metric tonnes or long tons.

The type of displacement your boat has will depend on its size and purpose, with light displacement boats usually being used for day sailing and racing, while moderate and heavy displacement boats are better suited for coastal and ocean cruising.

Light displacement boats are typically quite lightweight, with a hull weight of around 2 tonnes and a total weight of 4 tonnes or less.

These boats are often very fast and agile but can have limited load-carrying capacity due to their light construction.

Moderate displacement boats typically weigh between 4 and 10 tonnes, with a hull weight ranging from 3 to 8 tonnes.

These boats are best suited for coastal cruising and are usually made from heavier materials than light displacement boats. This makes them able to carry a greater load and handle rougher seas with more confidence.

Heavy displacement boats weigh more than 10 tonnes, with a hull weight of up to 15 tonnes.

These boats are built for long-distance ocean cruising and are designed to be sturdy and reliable even in heavy weather. As such, they are usually made from stronger materials than other types of boats and have a much larger load-carrying capacity.

D/L or DLR ratio- Displacement to length ratio

Displacement to length ratio (DLR) is a calculation used to measure the size of a sailboat.

It is determined by dividing the displacement (the weight of the boat) by the waterline length (the length of the boat that is in contact with the water when it is afloat).

The result of this calculation, also known as the DLR, can be used to compare different types of boats or to determine which type of sailboat is most suitable for specific conditions.

The formula for calculating the displacement-to-length ratio is: DLR = (Displacement/2240)/(0.01xLWL)^3 Displacement in pounds, LWL is Waterline Length in feet

Generally, sailboats with higher DLRs tend to have a more rounded hull shape and are better suited to deep-water sailing in heavy weather conditions.

Sailboats with lower DLRs tend to have a more slender hull shape and are better suited to shallow water sailing in light weather conditions.

Ballast is the weight of the boat that is not part of the boat’s structure. This weight can come from a lead, water, or other materials, and it is located in the bottom of the boat to help keep it stable in the water.

The amount of ballast affects the sail area, as more ballast will lower the sail area while decreasing ballast will increase the sail area.

This is because when there is more ballast in the boat, it will be pushed down into the water which reduces the area that a sail can reach. On the other hand, decreasing ballast will allow a sail to extend further.

Ballast is also important for maneuverability and stability; too much ballast and the boat will be sluggish and difficult to turn, while too little ballast could cause the boat to be unstable and even capsize.

Balancing the amount of ballast is key to achieving optimal performance for any type of sailboat.

CSF-Capsize screening formula

The capsize screening formula is a calculation that provides a good indication of the stability of a sailboat. It is the ratio of a boat’s displacement (weight) to its Beam (width).

Capsize ratio formula: Beam / ((Displacement/64.2)1/3) The beam is in feet. Displacement is in pounds

A good capsize ratio is generally considered to be between 1.33 and 2.0, although this can vary depending on the type of boat and its purpose.

A lower capsize ratio indicates that the boat is more stable, as it will be less likely to tip over in strong winds or waves. A higher capsize ratio indicates that the boat is more prone to capsizing.

Motion comfort ratio

Motion comfort ratio (also referred to as “Ted Brewer” ratio) is a measure of the overall stability of a sailboat.

Generally, a boat with a motion comfort ratio greater than 40 is considered stable and a boat with a motion comfort ratio less than 30 is considered unstable.

A boat with a motion comfort ratio between 30-40 is considered moderately stable. The higher the motion comfort ratio, the more comfortable the boat will be in rough waters.

Ted Brewer’s CR formula is: Displacement in pounds/ (.65 x (.7 LWL + .3 LOA) x Beam 1.333 ).

For instance, a boat with an LWL of 35 ft and a displacement of 10,000 lbs would have a motion comfort ratio of 37.5. This would indicate that the boat is moderately stable and should provide an adequate level of comfort in rough waters.

The motion comfort ratio was developed by Ted Brewer and has been used for many years as an indication of a boat’s stability.

It is important to keep in mind, however, that this ratio alone cannot give an accurate picture of how stable a boat is. Other factors such as hull type and keel type should also be taken into account when assessing a boat’s stability.

Ballast to displacement ratio

The ballast-to-displacement ratio is a measure of how much ballast is needed in relation to the weight of the boat.

The higher the ballast-to-displacement ratio, the more stable the boat will be and the less likely it will be to capsize.

the ballast-to-displacement ratio is important for ensuring the boat is adequately balanced and has good performance when sailing.

It is especially important for boats that have large sail areas, as larger sail areas require more ballast to keep the boat steady.

When considering a boat’s ballast-to-displacement ratio, keep in mind that a ratio of 40-50% is generally considered to be optimal. Any higher than that may be too much, while any lower may not be enough.

Your source for the latest news on yachts, boats and more. Read through our articles to find out how to compare boats and find the right fit for you!

Sailboat Ratios to Consider When Buying One

Nov 27, 2019

less than a min

The main sailboat ratios to look for when buying one!

Buying a boat is a big decision. It involves a lot of comparisons and a long process in order to find just the right fit for you. With so many models out there , the market is fully saturated, which makes it very hard to pick just one boat. To make the whole decision easier, there are a few parameters to consider, also known as sailboat ratios , which include the displacement to length ratio, the sail area to displacement ratio and the ballast ratio as the three main ones.

In order to make a completely informed decision on a boat it is important to have all these three parameters at hand and compare them. These parameters will indicate the performance and the comfort level of the boat. 

Understanding the main sailboat ratios

The three main parameters to take into consideration when you compare boats are the displacement-length ratio, the sail area-displacement ratio and the ballast ratio, respectively meaning as follows:

The displacement to length ratio shows how heavy a boat is. This is calculated in comparison with the waterline length and it is a non dimensional parameter resulting in a sole number. This sailboat ratio will show how heavy a boat is no matter of its size. Therefore it can only be used as a comparison parameter rather than to show the real weight of the boat. According to the displacement-length ratio, the boats are categorized as ultralight, light, moderate, heavy and ultra-heavy. 

The sail-area to displacement ratio is used to calculate the performance of a boat. It is also a non dimensional parameter which shows the relationship between the boat sail area and its displacement. According to this ratio boats are categorized as under performing, good performance vessels and high performance boats. 

The ballast ratio presents the ballast a vessel is carrying. Technically it shows the resistance a boat has to heeling. The ballast ratio is calculated as the weight of the ballast by half load displacement. The number you get is then multiplied by 100. A ballast ratio more than 40 will be more powerful and more resistant to wind. A good ballast ratio however will mean that the boat might not be as comfortable for leisure. A very high ballast ratio is probably a better parameter for sport fans. 

These are the three main sailboat ratios to consider when buying a boat. Therefore, make sure that all three are up on the good performance scale in order to have yourself a good boat. 

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Killer Whales Capsize Sailing Vessel in the Strait of Gibraltar Waters

A group of killer whales, also known as orcas, were responsible for capsizing a sailing yacht in the waters of the Strait of Gibraltar under Moroccan jurisdiction. The vessel, a 49-foot yacht called Alboran Cognac, was being operated by two individuals when it came under attack around 9 AM local time on Sunday, reports reveal .

This event marks one of many similar encounters, following an incident last November when a yacht was capsized after being struck by killer whales, causing damage to its rudder. Researchers suggest that orcas’ behavior, while seemingly playful or imitative in nature, can cause distress and lead to dangerous situations for sailors, as witnessed by the two occupants of Alboran Cognac who experienced hits to their hull and rudder leading to water ingress. The passengers were fortunately saved by an oil tanker which brought them to safety in Gibraltar, while their yacht was left adrift and eventually sank.

The occurrences have led to theories surrounding a pod of about 15 orcas, known by the moniker “Gladis,” which is inspired by the name of an orca, White Gladis, allegedly killed by vessel collision. Gladis and its pod members have been sighted engaging with ships in areas stretching from Portugal’s Atlantic front to the north-western waters of Spain since May 2020, and it’s believed that Gladis could also be part of this recent assault.

Rumors of the orcas’ motives variably point to notions of revenge, environmental aggravations like climate change or maritime noise pollution, and even outlandish conspiracy theories, but experts suggest that orca behavior is fueled by their complex societal structures and shared rituals. Orcas, being powerful enough to genuinely harm humans, seem instead to mess with vessels out of intrigue or pleasure.

Specialist Lance Barrett-Lennard, PhD from the Raincoast Conservation Foundation, shared his insights with Salon in June, describing these episodes as part of a “cultural revolution” among orcas. He posits that such behavior, if linked to immediate benefits such as food or essential survival advantages, may dissipate fairly swiftly, anticipating future developments in these interactions.

about orcas and whales

FAQ Section

Orcas exhibit complex behaviors and may engage with boats out of curiosity, playful behavior, or social interactions within their pod. Retribution for harm caused to them, a response to environmental stressors, or abstract notions such as a reaction to climate change are also speculated theories.

While orcas are powerful and could potentially harm humans, the reported incidents involve damage to vessels rather than direct aggression toward people. Nevertheless, such interactions can lead to dangerous circumstances for those on board.

In the incident involving the Alboran Cognac, the passengers were rescued by a nearby oil tanker and taken to Gibraltar for safety.

There have been documented cases of orcas interacting with boats along the coastlines of Portugal and Spain since May 2020. It is an ongoing subject of study and interest among marine biologists and animal behaviorists.

Research and monitoring are ongoing to better understand orca behavior and interactions with human maritime activities to prevent future incidents.

The recent capsizing of a yacht by orcas in the Strait of Gibraltar is a complex event highlighting the intricate relationship between humans and marine wildlife. With continued research into orca behavior, there is hope for mitigating such encounters, ensuring safety for both seafarers and the marine inhabitants. While the orcas’ motivations are not fully understood, the events serve as a stark reminder of the powerful and unpredictable nature of wildlife and the need for respectful coexistence.

The post Killer Whales Capsize Sailing Vessel in the Strait of Gibraltar Waters appeared first on Kevin Hearld .