yacht capsize ratio

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What is a Sailboat Capsize Ratio and how to measure it

Aug 05, 2020

less than a min

As a boat owner, there are many formulas and ratios that you should know about. Do not worry if you are new to the whole marine and naval realm, however. There is always time to learn more if you are willing to. Here is a summary of what a sailboat capsize ratio is. 

A sailboat capsizes ratio is a parameter used to show whether a boat can recover from an inverted, capsized position or not. This term was mainly developed after the Fastnet race disaster . This was a 1979 race where a storm destroyed several yachts during the last day of the race, also causing 19 victims. Since then, tank tests have been developed to offer a prediction on how likely is a boat to recover after capsizing. 

The capsize ratio is a good indicator of what the boat is designed for. For example, if a boat has been designed to be used at sea, then it will have been equipped with features to make it more stable and prevent it from flipping over or capsizing. The capsize screen in this case can have a value below 2. 

A capsize of over 2 does not necessarily mean a bad thing. Boats with such a capsize value are better for coastal cruising as they offer higher form stability and a larger interior. In addition, these boats sail closer to the shore which allows them to return to safety in no time in case of a disaster.

How to measure the sailboat capsize ratio

There are several online calculators that can help you figure out your sailboat’s capsize ratio . These calculators are based on the capsize screening formula defined as below:

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

The displacement in this formula is measured in pounds . This formula does not take into consideration the location of the ballast or the shape of the hull. In terms of understanding the value here’s the gist. The lower the value, the less likely is the sailboat considered to capsize. If the value is 2, then the boat is still accepted to take part in races, although this might depend on the race committee. 

The sailboat capsize ratio is also related to the displacement and beam. Therefore, two sailboats can have the same value if they also have the same displacement and beam. Their stability however could differ although they have the same capsize value. 

All in all, the sailboat capsize ratio is more important when related to racing sailboats used further from the shore. This parameter is not a crucial one to take into consideration when analyzing a chartered yacht or any sailboat intended for pleasure. 

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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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• Sailboat Guide

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.

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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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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!

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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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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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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

Sail Far Live Free

Comfort, capsizing, and sailcalc.

"This is a ratio that I dreamed up, tongue-in-cheek, as a measure of motion comfort but it has been widely accepted and, indeed, does provide a reasonable comparison between yachts of similar type. It is based on the fact that the faster the motion the more upsetting it is to the average person. Given a wave of X height, the speed of the upward motion depends on the displacement of the yacht and the amount of waterline area that is acted upon. Greater displacement, or lesser WL area, gives a slower motion and more comfort for any given sea state.

Beam does enter into it as wider beam increases stability, increases WL area, and generates a faster reaction. The formula takes into account the displacement, the WL area, and adds a beam factor. The intention is to provide a means to compare motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch."

)

LOA	Pearson 36-2	36.27    39.5833     29.68    33.5     12.36    12.652     15107    18000     663    701.3     2    1.93     7.3    7.76     17.36    16.34     258    214     2.4    2.65     25.69    26.59     1311    1514 LOA Irwin 28     28.3    28.25     22.5    23.5     9.00    9.58     7800    13540     381    546     1.84    1.61     6.36    6.5     16.74    15.38     272    466     2.56    2.45     24.28    41.08     707    804 Very nice article to explain the "numbers". Your Irwin 28 shows as an excellent coastal cruiser from the "Good Old Boat" era. She has beautiful lines to me also-proportions look right and I am a big fan of a nice sheerline as I have been spoiled by my C&C25-MkI and sisterships 27 MkI-IV/30 MkI from the 70's-early 80's. Recently sold our C&C and looking for a coastal cruiser in the 28-3o ft range and did not have this on my list of prospects. One just popped up this week locally and I definitely want to see her. Thanks again for you articles-I am sure they have been and will be helpful to other new and salty sailors. Rob Post a Comment Popular posts from this blog, top 10 favorite affordable bluewater sailboats, go small and go now 5 pocket cruisers to take you anywhere. Escape to the Sea: How to get from the Great Lakes to the Caribbean Sails & Canvas Hull & Structure Maintenance Sailing Stories Sailing Tips Boat Reviews Book Reviews The Dogwatch Select Page 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. Related Posts A DIY Sailboat Shower – Rub a Dub Dub July 15, 2020 Up the Mast July 25, 2019 Foul Weather Shorts November 1, 2018 Insights on sidelights May 1, 2017 Current Edition Join Our Mailing List Get the best sailing news, boat project how-tos and more delivered to your inbox. You have Successfully Subscribed! Capsize – understanding the risks by Simon Jollands | Boat Handling , Emergencies , Preparation A skipper should know how their boat will cope with rough seas. By working within known limits and understanding the risks, then the chances of a capsize occurring are much reduced. Safety is all about improving the odds. When considering the odds of a boat capsizing, knowing the limitations of its design and stability are critical. In order to do this, it helps to understand the basic principles of how a boat remains upright. Basic principles A boat remains upright because of the way its weight and buoyancy interact. The basic principle of buoyancy is that the upward buoyant force on a body immersed in fluid is equal and opposite to the weight of the fluid that the body displaces. The weight of the fluid displaced is known as displacement and the displaced water has an up thrust, or buoyancy, which is equal to the weight of the boat. The displaced water has a central point, or centre of buoyancy, which varies according to the shape of a boat’s hull and keel. The centre of buoyancy is not to be mistaken for the centre of gravity. The weight of a boat is distributed along its length, pushing the entire vessel downwards.  All the weight acts downwards through a central point, or centre of gravity, which is similar to the fulcrum or central point of a seesaw.  All the structure and the distribution of weight aboard contribute to a boat’s centre of gravity. To keep a boat stable in the water and prevent it from toppling over requires the centre of gravity to be low, which is greatly helped by having a deep, heavy keel and an engine below the waterline. Angle of heel If a sailing boat heels over in a strong gust of wind or is forced over by a big wave, then it will right itself once the gust or wave has passed. When a boat is upright then the force of gravity is directly opposed to the force of buoyancy.  As the boat heels over the centre of buoyancy moves outwards and acts as a lever does, pushing upwards with an increasing force. This is fine up to a point, but eventually as the boat continues to heel the righting lever effect reduces and eventually is lost and then the boat will capsize and float upside down. This point is known as the Angle of Vanishing Stability (AVS). Boats with a high AVS will resist becoming inverted and return to the upright position quickly in the event of a knockdown. These include narrow, heavy displacement boats with a deep draft which can heel to 120º or more. Once capsized, only a small amount of further rolling moves the hull into the positive righting area and the boat comes back upright. Boats with wide beams and shallow drafts tend to have high initial stability but may capsize at 90º of heel and will not always be self-righting. Righting moment curve Boat manufacturers publish righting moment curves of their yachts to show the stability characteristics of their designs. In Europe the Recreational Craft Directive (RCD) states that pleasure yachts between 2.5m and 24m must carry builders’ plates to categorize their boats in either Category A (Ocean), B (Offshore) or C (Inshore) and meet minimum standards of stability. Breaking waves Rules and regulations are one thing, but the force of steep breaking waves can knock any yacht down in coastal waters, especially if it is caught beam-on. Research has shown that the most significant factor in capsize is whether a wave is breaking or not. If the wave is greater in height than the beam of the boat, then it can easily knock the boat over. Tests carried out at Southampton University in England have shown that almost any boat can be capsized by a wave equal to 55% of the boat’s overall length. Such waves may occur where the seabed suddenly shelves towards the coast, or where wind is blowing against tide. This research points to the fact that yachts seeking shelter often find themselves in greater danger when approaching harbours than when coping with a storm further out to sea. Being prepared If you are well offshore in rough weather, consider your options. If needs be, heave to and ride out a storm as the boat will be more stable and comfortable, but check you have sufficient sea room to drift downwind and are not approaching a lee shore.  Another option is to lie ahull, with no sail up and the helm tied to leeward. If conditions worsen then the next stage is to lie to a sea anchor or drogue, which will prevent the boat from meeting waves beam on and reduce the vessel’s drift rate. Don’t automatically head for the nearest harbour or your intended destination. Check first what the conditions are likely to be there, by considering the state of the tide, wind direction and whether there are danger areas such as headlands and sand bars to contend with. Check out all the alternatives and be prepared to alter your plans in order to opt for a safe option. Tips to prevent capsize: Know your boat’s limitations. Don’t overload the boat. Pump the bilges regularly. Keep a generous margin of safety. Know when it is best to yield to conditions, rather than fight them. Avoid areas known for overfalls and tide rips. Avoid being caught beam on to breaking waves. [fts_facebook type=page id=820902544629856 access_token=EAAP9hArvboQBAMMusRb1XctIwYq9fUcSZCVNDQAMjkZCiqAIMiZBkawPJZB3VkeSsH6gCIDfIZAslzZBRAEXYdesg0fu11YIst1FXtABBwdULjOsYFGUYqNujLSxRIWxKAcqm7bb9dmAgzJDZCVhkRj6r9useCQqJr4wJnxkBv909ySYxqj7hYl posts=4 height=650px description=no posts_displayed=page_only] Recent Posts Boating Etiquette: Do’s and Don’ts on the Water Navigating narrow channels DIY boat upgrades: Budget-friendly projects to enhance your (older!) boat Boat Security: Protecting your vessel from theft & vandalism Learning about diesel engine maintenance 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. There are two main causes of capsizing. One of them is the result of the wind overpowering the boat and its crew so that the boat heels excessively until it fills with water and capsizes to leeward. The other is normally the result of a crewing error in strong winds, usually on a downwind course, so that the boat becomes unbalanced and capsizes, generally to windward. Although on the whole one-designs allow a fairly large margin for error on the part of the crew, racing one-designs don't, as they are more sensitive owing to their relatively larger sail area and lighter hulls. Capsizing is an ever-present possibility in all unballasted boats, and it is important that you know how to deal with it. You need to be familiar with the correct righting techniques which should form part of your basic seamanship training. As a beginner you would be well advised to deliberately capsize your boat , but under supervision, to learn how to right it; your confidcncc will be improved if you have already capsized in a controlled situation. All one-designs havesomebuoyancy sothere is no danger that they will sink, provided that the buoyancy has been checked before launching. The amount of buoyancy is important (see pages 46—7): too much can cause the boat to blow away on its side or float so high in the water that the upturned centreboard is out of reach. If you buy a new boat, capsize it in shallow water to determine its behavior so that you can adapt your righting techniques accordingly. The method you use will depend to some extent on the circumstances of the capsize and the type of boat. Before the development of the scoop method (shown right), a crew trying to right their boat had to swim it around head-to-wind so that it would not blow over again as soon as it was righted; alternatively, they sometimes found they had to lower the sails before attempting to bring the boat upright. The scoop method, however, has the advantage of permitting a boat to be righted irrespective of its position relative to the wind as the crew is already aboard to act as ballast. Some more complex capsizes will require modifications of the scoop method or even different techniques (see pages 88—9). Whatever the circumstances of the capsize, the crew should stay with the boat. It is much more visible to a rescue launch than a lone swimmer and the shore may well be further away than it appears. Righting a boat — scoop method In this method, the crew is scooped up inside the boat as it is brought upright by the helmsman who stands on the centerboard and pulls on the jib sheet. Because the crew is already aboard when the boat comes upright, he acts as ballast and prevents the boat from capsizing again immediately after righting When the boat capsizes to windward, the crew must wait for the sail to swing over to the other side of the boat before leaning over to help the helmsman aboard. Both helmsman and crew must understand their respective tasks and carry them out accordingly. The crew must also take care not to pull on the boat before the helmsman has climbed onto the centerboard or it may invert on top of him. Lightweight racing boats are particularly prone to inversion. The techniques for dealing with an inverted boat are described on page 89. 1 Crew checks that the centerboard is in the fully down position. He then sorts out the mainsheet while the helmsman swims to the transom and checks the rudder fitting is still in place. 4 The crew lies down in the boat, holding onto the toe straps or the thwarts, while the helmsman climbs onto the centerboard, using the jib sheet as a lever if necessary. Position of the helmsman The helmsman must take care to stand at the root of the centerboard, as close to the boat as possible, to prevent it breaking under his weight. He must be ready to let go of the jib sheet and grasp the side decking to lever himself aboard the boat as it comes upright. Throughout the righting sequence both helmsman and crew should talk to each other so that they know what is happening. 2 The crew holds the transom steady while the helmsman, taking the mainsheet over the rudder, swims to the centerboard. using the mainsheet as a lifeline until he gets there 3 When the helmsman has reached the centerboard and grasped it. the crew swims around to the inside of the boat, sorts out the upper jib sheet and throws it over to the helmsman. 5 The helmsman, after checking that the crew is ready, stands on the centerboard as close to the boat as possible and starts to pull on the jib sheet to begin the righting movement. 6 The helmsman continues to pull on the jib sheet until the boat is nearly upright and scrambles aboard over the side decking. Both crew members then prepare the boat to sail off immediately. 2 She grabs the jib sheet and scrambles out onto the centerboard. standing as close to the root of the board as possible. 3 The helmsman grasps the lower toe straps and is scooped aboard as the crew rights the boat by pulling on the jib sheet. Righting a trapeze boat In racing boats if the crew is not out on the trapeze you can use the normal righting method. However, for the occasions when the crew is trapezing. both helmsman and crew have to learn how to react very quickly in the event of capsize. They must perfect a righting technique which is rapid and efficient. The first priority is for the crew to unhook and climb out on the centerboard as rapidly as possible to prevent the boat from inverting. The helmsman performs the role normally carried out by the crew and is scooped up into the boat in the usual way. 1 The trapezing crew moves her weight back onto the gunwale as the boat capsizes and unhooks rapidly from the trapeze. 2 He swings himself onto the centerboard. and rights the boat by pulling on the gunwale. 1 As the sail starts to hit the water, the helmsman should grasp the upper gunwale and begin to lever himself up. ready to climb over the side as quickly as possible. Righting single-handed Single-handed boats can be difficult to right as the center-board floats high in the water and the boat can blow away from you. If you sail single-handed you should develop a technique whereby you do not actually fall in the water, but start to scramble up over the gunwale as the sail hits the water, ready to right it by standing on the centerboard and pulling on the gunwale. If you do fall in the water, the boat can sometimes be righted by grasping the bow and sinking it so that the boat rotates to its normal floating position. 2 Crew then bundles spinnaker into pouch (or chute) before starting normal righting sequence the other presses down hard on the stern to break the air seal. Once in the normal capsize position, the boat is righted in the usual way. If the centcrboard has not retracted the job is made much simpler because one person can use it as a lever. It is important to make sure the jib sheet is brought over forward of the centerboard to prevent it slipping backwards. Righting when a spinnaker is set Righting an inverted boat If the crew are slow to react to a capsize, the boat can easily invert. The air is then trapped under the hull and the boat forms a seal with the water which can be difficult to break. The method you use to right an inverted boat will depend on the position of the centerboard. If you capsize with the centerboard fully retracted, or if it retracts during the capsize, recovery will be made harder because you do not have it to use as a lever to right the boat. Whatever the method, the boat should be righted so that the mast comes up towards the wind. This will then make recovery from the normal capsize position much easier, and will prevent the boat from capsizing again. It is best if one person pulls on the jib sheet, standing on the gunwale, while If you have the misfortune to capsize your boat with the spinnaker set. the first task is to release one corner of the spinnaker so that it doesn't act as a sea anchor. The next job is to get the spinnaker down. If the boat inverts with the spinnaker set, bring it up to the normal capsized position before starting to right it in the usual way. 1 Crew finds one corner of the spinnaker and undoes the sheet from the clew. 3 Both helmsman and crew continue pulling until boat gradually turns over until it lies in normal capsized position. 4 Crew climbs onto centerboard aided by helmsman and righting sequence (see previous page) is followed in usual way. 1 Helmsman finds a jib sheet from inside boat. Helmsman and crew swim to other side of boat and crew climbs onto gunwale and grasps centerboard. 2 With helmsman and crew both kneeling on boat, crew starts to pull on centerboard while helmsman pulls on jib sheet If you capsize in shallow water your mast may dig into the mud so that you have to be towed off. Make sure that the righting line from the towing boat is clipped or tied to the shroud and taken over the hull (below). Where possible, arrange for the boat to be pulled upright against the wind (right). Every one-design should have a painter attached at the mast and led through a bow fitting. If a single boat is towed in calm conditions it can be fastened alongside the towing boat (right) or towed behind the rescue boat. If more than one boat is towed, each one can be attached with a rolling hitch (see page 532) to a rope trailed from the rescue boat. Crew under sail Crew under hull There is plenty of air inside the hull. Swim to an outer edge and push yourself under the side decking to get out Crew trapped Now and again, as the result of a capsize, the crew gets trapped either under the sail or in the inverted hull. Neither situation is dangerous although it can be alarming if you do not know the correct procedure to deal with it. Crew beneath sail Push your hand up and make an air pocket in the sail. Then, keeping one hand above your head to push the sail, work your way,using a seamline to guide you, to the outside edge. Continue reading here: Man overboard Was this article helpful? Recommended Programs Myboatplans 518 Boat Plans Related Posts Broad Reach With Tide - Sailing Procedures Reefing - Sailing Procedures Simple capsize drill - Sailing Techniques Basic Rescue Tips for Water How to tack - Sailing Procedures Ketch Schooner Yawl Cutter Readers' Questions Can a sailboat capsize? Yes, a sailboat can capsize. When a sailboat capsizes, it means that it overturns or flips upside down. This can happen due to various factors such as strong winds, improper sail handling, excessive weight on one side, or by hitting a large wave or obstruction. Capsize can be dangerous and may lead to injuries or even the sinking of the boat if not handled properly. Sailors are trained to prevent capsize and to know how to respond if it happens. What should you do if your boat capsizes and floats away? If your boat capsizes and floats away, it is important to stay calm and act swiftly. Here are the steps you should take: Stay with the boat: If possible, try to stay near the capsized boat because it can provide you with some buoyancy and increase your chances of being spotted by rescuers. Cling onto the boat or any floating debris. Assess your supplies: Check if you have any floating supplies near you such as life jackets, oars, or emergency kits. These can provide assistance until help arrives. Signal for help: If there are other boats or people nearby, make yourself visible by waving your arms, shouting, or using any signaling equipment you have. If you have a whistle or flare, use them to attract attention. Stay visible: If no immediate help is available, focus on remaining visible. If you have bright-colored clothing, put it on or use it as a flag. Try to paddle or swim closer to the shore or any potentially safer location. Conserve energy: After the initial panic, try to conserve your energy. Avoid excessive swimming or thrashing around, as it can increase fatigue and hypothermia risks. Instead, tread water or float to preserve energy. Use the HELP position: If you are alone, use the Heat Escape Lessening Position (HELP) technique to reduce heat loss. It involves crossing your arms tightly against your chest while drawing your knees up towards your body. This position helps reduce heat loss from the armpits, chest, and groin. Stay positive and hydrated: Mental resilience is crucial in survival situations. Keep a positive mindset by focusing on positive thoughts or engaging in mental exercises. If you have access to drinking water, consume small amounts periodically to stay hydrated. Remember, the best course of action is to prevent a situation like this from happening by equipping yourself with proper safety measures, such as wearing life jackets, knowing how to swim, and being familiar with boating safety protocols. What causes a boat to capsize? A boat can capsize for a variety of reasons, including strong winds, waves, improper weight distribution, or an uneven hull or center of gravity. Other causes may include an overloaded boat, a collision, or striking a submerged object. Prolonged exposure to wind, waves, and excessive speed can also cause a boat to capsize. Forums New posts Unanswered threads Register Top Posts Email What's new New posts New Posts (legacy) Latest activity New media Media New media New comments Boat Info Downloads Weekly Quiz Topic FAQ 10000boatnames.com Classifieds Sell Your Boat Used Gear for Sale Parts General Marine Parts Hunter Beneteau Catalina MacGregor Oday Help Terms of Use Monday Mail Subscribe Monday Mail Unsubscribe Capsize Ratio? Thread starter Ducati Start date Oct 31, 2009 Forums for All Owners Ask All Sailors What is a quick answer for the meaning of "Capsize Ratio" as it relates to sailboats? Our boat has a ratio of 1.95. Thanks   it is just the boat You are a significant factor in wither the boat capsizes or not. Learn weather and weather handling skills before you need them. Practice in a gale near home first. FWIW   Thanks My quick math tells me that most boats have a beam that is about 1/3 that of the length. Our boat has a beam of 11.4' x 36. So is this a good or bad ratio. Regards   David in Sandusky Designers Intent Experience and testing make it clear that if a boat is hit broadside by a breaking wave taller than its beam, it willl capsize, regardless of its design, or low capsize screening ratio. Capsize ratio indicates the likelihood that a boat will recover from an inverted, capsized position. It was developed during tank tests conducted after the Fastnet race disaster. Because it has been around for a while, the capsize ratio tells you about the designer's intent for a design. Boats designed for blue water cruising will have many features to support that purpose, including a capsize screen below 2. On the other hand, 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, especially when the beam is carried aft. - Depending on the hull shape, a beamy boat may be more likely to plane on a reach. And coastal cruisers can usually return to port before conditions build breaking waves tall enough to capsize the boat.   You can look your boat up here: http://image-ination.com/sailcalc.html   Stuff happens Franklin, in the Fastnet race, there were some good skippers who were caught when the storm blew up. Blue water sailing means you have to take the weather that comes - and unseasonable storms do happen. If a helmsman loses contol of the boat for a moment, or if fatigue, injury or illness force lying ahull, or a wave comes from an unexpected direction...then a boat can be capsized. A larger wave can capsize a boat without catching it broadside. Once inverted, a boat with a low capsize ratio is more likely to recover to an upright position. With or without the mast and rigging, that's a whole lot better than staying inverted!   Stuff happens Like David said, stuff happens and happens and happens. http://www.youtube.com/watch?v=eiRgKXs92fc&NR=1   Wow Something to say about having a ton of lead in the bottom of your boat!!!   dserelle, Are you saying that the capsize ratio and the capsize screening factor are different? Your post seems to say the capsize ration is a measure of resistance to capsize and the capsize screening factor is a measure of how a boat may recover from capsize. Is that correct? Can you supply the parameters of both?   When I was looking at boat designs 30 years ago "righting moment" was the charictaristic that we looked for. iIrealize it is but one factor and the engineers have combined righting moment with several other factors to come up with the capsize factor or ratio. Degrees of stability was another factor that concerned us. How far could you roll a boat and expect it to recover and not continue to roll until it was turtled?   As it relates to a sailing vessel the ratio by itself is worthless. Ratios can be misleading as they are based in proportions and the winds and seas just come in one size. If you provide us with the size and make of your boat perhaps we can best advise on its capabilities.   Keep in mind, some say if a wave comes long and capsizes you and it stays down, another wave will come by and right you as long as the sheets are released. Personally, I will never be taking a wave on the beam like that. At the very worst, I'lll deploy the jsd and go below and sleep it out.   The next wave Actually, the capsize ratio indicates the chances that the next wave(s) will right the boat. A chief value of the different ratios we use to describe a boat design is that they _do_ apply to widely different designs.   Testing the extremes Capsize ratio is telling us about the impact of form stability versus righting moment in a boats designed shape. With extreme beam, and no ballast, a catamaran has the form stability to stay upright in high winds - but once it's turned over its going to stay that way. On the other hand, a cylinder with a lead keel on it is always going to return to an upright position. The Island Packet design comes to mind. Capsize ratio is just an elegant way of indicating where a design fits between those two extremes.   Re: Testing the extremes 1   This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register. By continuing to use this site, you are consenting to our use of cookies. 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Equipment & Dinghy Anchoring & Mooring Photo Categories Member Galleries Life Onboard Sailing in the Wind Power Boats Cruising Destinations Maint. & Boat Building Marine Life Scuba Diving & Divers General Photos Recent Photos Listing Categories African Cats view more » Crew Wanted Crew Available Enhance Your Account Meet the Mods Meet the Advisors Signup for The Daily Cruiser Email   > > Please support our sponsors and let them know you heard about their products on Cruisers Forums. 27-11-2006, 13:34   Boat: Lancer 1976 28' - Green Eyed Lady 28 with a ratio of 1.76. This figure is very pleasant for me and my , just in case. But I did some in bigger around 40' and I discover that in many recent-new models the ratio goes bigger than 2.0 (with the risk of capsize). Mi question is: bulb and very low ballast make this ratio useless? 27-11-2006, 13:59   Boat: Gozzard 36 Mi question is: bulb and very low ballast make this ratio useless? 27-11-2006, 14:46   Boat: It’s in French Polynesia now a . Where one may capsize in surf, may not capsize in a blowdown. It's design vs. ballast. Some keels (winged) are treacherous on a tall wave where others will slide down the side of a swell with ease allowing the to stay more up right. Ballast, lower in the does create a lower COG but then again if it has a the drag is higher. The boats use the long keel with the bulb but are usually lighter in weight for their size. It's more for resistant rather then off shore stability. They're not good on steep close waves. Cat's for instance seem to be able to take steep angles UNLESS they have down or deep skegs..................._/) 27-11-2006, 18:24   Boat: Farrier F41 Catamaran - Endless Summer at least have to pass a heel angle test which verifies the stability curve at one point, but in the US there's no guarantee that the numbers actually mean anything at all. For example, a light boat with little tankage and aggressive assumptions about might look great on the capsize screening formula, but when you factor in 100 gallons of fuel/water lashed to the rails it could be much less safe than a similar boat with sufficient tankage at level. I don't think that looking at boats with a "capsize ration less x" or a "vanishing stability angle greater than y" is going to give you meaningful results. These numbers might be useful to compare two very similar boats; the deep keel and the model of the same boat, for example. -Scott 27-11-2006, 19:03   Boat: Gozzard 36 28-11-2006, 01:24   Boat: (Cruiser Living On Dirt) : There are links to several excellent sources. There’s much more to “stability” than a good CSF* number. * of America came up with a simple formula to determine if a boat had capability. The CSF compares beam with displacement since excess beam contributes to capsize and heavy displacement reduces capsize vulnerability. The formula is the maximum beam divided by the cube root of the displacement in cubic feet; B/Displ.333. The displacement in cubic feet can be found by dividing the displacement in pounds by 64, of course. The boat is acceptable if the result of the calculation is 2.0 or less but, of course, the lower the better. For example, a 12 meter yacht of 60,000 lbs displacement and 12 foot beam will have a CSF Number of 1.23, so would be considered very safe from capsize. A contemporary light displacement yacht, such as a 311 (7716 lbs, 10'7" beam) has a CSF number of 2.14. Based on the formula, while a fine coastal cruiser, such a yacht may not be the best choice for ocean passages. 28-11-2006, 10:14   Boat: Lancer 1976 28' - Green Eyed Lady , but I´m not american. In fact I always consider that in any field you can't have a factor which explain multicausal problems. The basis of my question is, of course, (the relative you can expect in the sea), and it depends also of chance, but basically is the result of many factors, including the experience and knowledge of sailors, the prudence of your decisions and the analysis of sea and wheather conditions. But the boat you ride is an important factor and there are a discussion, as I saw in , about the value of these ratios and or course is only a point of reference, not the final word. In my view, for my lack of experience and knowledge, they seems a strong reference about the boat capacity to handle strong seas. But this idea seems weak when I saw also that Benetaus, Bavarias, Hunters, Catalinas, etc exceed the sacred 2.0 I have a little boat which make me very very happy, but I sail in a relatively safe (the Gulf of Nicoya and the Pacific Coast in Costa Rica), so my question may be a rhetorical one, but when I must face winds and waves bigger than ussual with my child and wife (my responsability), I find peace of mind considering that my little boat can heel and move without capsize at least a breaker bigger than 15 feet hit us in one side. And if this happen (a very little possibility here and not if I have something to do about) my boat can handle that and right itself. So thanks again. 28-11-2006, 13:04   Boat: VandeStadt IOR 40' - Insatiable of 1979, the subject was revisited in some by the RORC and the stability/righting tests for yachts was tightened up considerably. Many IOR designed boats ended up having to put additional lead in their keels to meet the new righting requirements. Nevertheless, most righting calculations are based on bare boat / empty , etc. Sensible distribution of baslast is important (simple - the lower the better). Having said all that, good seamanship is probably the most important factor in preventing knockdowns. 28-11-2006, 17:16   Boat: Gozzard 36 Many IOR designed boats ended up having to put additional lead in their keels to meet the new righting requirements. 28-11-2006, 20:10   Boat: Hartley Tahitian 45ft. Leisure Lady 29-11-2006, 00:19   Boat: (Cruiser Living On Dirt) 29-11-2006, 04:32   Boat: Farr 11.6 (AKA Farr 38) Synergy formula and motion comfort index formulas were developed at a time when boats were a lot more similar to each other than they are today. These formulas have limited utility in comparing boats that are very similar but are totally useless and misleading in most cases. . . (Yes, I know that no one would install a 500 lb weight at the top of the but decks, heavy decks, wooden or spars can easily have that kind of impact.) The boat with the weight up its mast would appear to be less prone to capsize under the capsize formula, and would appear to be more comfortable under the Motion Comfort ratio. Nothing would be further than the truth. That is why I see these formulas as being worse than useless. 29-11-2006, 10:26   Boat: Hartley Tahitian 45ft. Leisure Lady but had no idea how to explain it in the excellent way you did. Thanks. 19-01-2007, 17:32   21-01-2007, 19:56   Boat: Farr 11.6 (AKA Farr 38) Synergy 380. Under the CSF the would seem to be substantially the more stable, and yet if you compare full volume analysis of LPS the Farr has an LPS something over 120 (not to be mistaken for an IMS LPS which is only 107 for the Farr) vs the Catalina which I have seen quoted as being is down around 115 degrees. But the LPS does not tell the whole story. The Farr has a significantly higher ballast ratio, shallower canoe body, and a narrower beam than the Catalina, all of which should give the Farr a much higher stability advantage. Yet there is that old CSF saying the Catalina should be more stable. If someone bought the Catalina 380 over the Farr 38 expecting greater stability, they would have been sorely mislead. If you actually read the various post storm disaster studies, you would find that beam and displacement are comparatively small factors in actual capsizes. The single common factor that all of the studies show seems to be waterline length. Ballast ratios, (more specifically vertical center of gravities relative to vertical center of buoyancy), and dampening being the only identified secondary factors that seem to impact capsize. None of these, except length are actually in the capsize screen formula. Respectfully, Jeff Thread Tools Rate This Thread : Posting Rules post new threads post replies post attachments edit your posts is are code is are are are Similar Threads Thread Thread Starter Forum Replies Last Post Stede Monohull Sailboats 34 07-07-2015 14:29 Stede Liveaboard's Forum 50 21-07-2011 11:43 eskfreedom Multihull Sailboats 39 19-02-2008 11:34 fujiwara takumi General Sailing Forum 10 26-08-2004 02:18 maui Monohull Sailboats 33 25-05-2004 12:12 - - - - - - - Privacy Guaranteed - your email is never shared with anyone, opt out any time. 198 IMAGES Why does a boat capsize? Capsize Transverse stability: sailing yachts at sea, wave impacts, knock-downs What Is Capsize Ratio And How Is It Calculated? Capsize Why does a boat capsize? VIDEO Terrifying Wave Hits And Capsizes RC Ship MIni 40 RC Trimaran at Champion Lakes 8 January 1.mpg Crash and Burn Anvera Yacht A yacht’s anti-capsizing test for rough seas #Shorts Why are they doing this?! 🤨 COMMENTS What is a Sailboat Capsize Ratio and how to measure it Here is a summary of what a sailboat capsize ratio is. A sailboat capsizes ratio is a parameter used to show whether a boat can recover from an inverted, capsized position or not. This term was mainly developed after the Fastnet race disaster. This was a 1979 race where a storm destroyed several yachts during the last day of the race, also ... What Is Capsize Ratio And How Is It Calculated? 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 ... Sailboat Calculator PART 3: RATIO RESULTS BOX. Results: This area displays the parameters of the boat selected. Do not enter values here. Click on any of the Derived Quantities boxes for an explanation of the box ... Capsize Screening Formula: S#: Hull Speed: Pounds/Inch Immersion: RIG MEASUREMENTS: SA Fore: SA Main: SA Total: (100% Fore and Main triangles) Comparing capsize and comfort rates of boats 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. Sailboat Guide 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. Capsize Screening Formula for Boats and How to Measure It 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. ... Knowing a boat's capsize screening number raises awareness of its stability limits. Boaters can avoid overloading the ... Capsize Ratio formula is the maximum beam divided by the cube root of the. displacement in cubic feet: Capsize Ratio = Beam/Displacement.333. The displacement in cubic feet can be found by dividing the. displacement in pounds by 64. The boat is acceptable if the result of the calculation is 2.0. Understanding Sailboat Design Ratios 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 ... 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 ... Capsizing Seawise University capsized after being gutted by fire in 1972. Capsizing or keeling over occurs when a boat or ship is rolled on its side or further by wave action, instability or wind force beyond the angle of positive static stability or it is upside down in the water. The act of recovering a vessel from a capsize is called righting.Capsize may result from broaching, knockdown, loss of ... Sail Calculator 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. ... the Capsize Screening number is a ... How Often Do Sailboats Capsize: A Comprehensive Guide 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? Assessing Stablity 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. What are the meanings of the capsize ratio and the comfort ratio Author. Motion Comfort Ratio was developed by Boat Designer Ted Brewer. The formula predicts the speed of the upward and downward motion of the boat as it encounters waves and swells. The faster the motion the more uncomfortable the passengers. Thus, the formula predicts the overall comfort of a boat when it is underway. Comfort, Capsizing, and SailCalc The comfort ratio formula is as follows: Displacement in pounds / (.65 x (0.7 LWL + 0.3 LOA) x B^1.333). Brewer says ratios vary from 5.0 for a light displacement daysailer to the high 60.0's for a super heavy ocean cruiser. Next, let's define the "Capsize Screening Formula" (CSF), a sometimes controversial mathematical equation that is suppose ... Capsize 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. How to Choose a Safe Cruising Sailboat Capsize Screening # = Boat's Max. Beam (feet) / Cube Root (Gross Displacement / 64) In English: take the boat's gross displacement in pounds, divide it by 64 and then take the cube root of the quotient. Now, divide the boat's maximum beam in feet by the cube root figure. The resulting number should be 2 or less. Capsize By working within known limits and understanding the risks, then the chances of a capsize occurring are much reduced. Safety is all about improving the odds. When considering the odds of a boat capsizing, knowing the limitations of its design and stability are critical. In order to do this, it helps to understand the basic principles of how a ... Sailboat Specifications 101: Explained For Beginners 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. Capsize screening formula The capsize screening formula (CSF) is a controversial method of establishing the ability of boats to resist capsizing. It is defined for sailboats as: Beam / ( ( Displacement /64.2) 1/3 ), with Displacement measured in pounds, and Beam in feet. A lower figure supposedly indicates greater stability, however the calculation does not consider ... Capsizing A boat can capsize for a variety of reasons, including strong winds, waves, improper weight distribution, or an uneven hull or center of gravity. Other causes may include an overloaded boat, a collision, or striking a submerged object. Prolonged exposure to wind, waves, and excessive speed can also cause a boat to capsize. ... Capsize Ratio? Once inverted, a boat with a low capsize ratio is more likely to recover to an upright position. With or without the mast and rigging, that's a whole lot better than staying inverted! Ted. Jan 26, 2005 1,258 C&C 110 Bay Shore, Long Island, NY Oct 31, 2009 #9 Stuff happens ... Capsize Ratio's Re: Capsize Ratio's. The Capsize Screening Formula is a quick and dirty formula for indicating whether a naval architect should do more analysis of a boat's capsize resistance. The more involved analysis looks at the roll moment of inertia of a boat to determine its susceptibility to capsize due to wave action. Capsize ratio Conditions will determine what will actually capsize a boat.Where one may capsize in surf, may not capsize in a blowdown. It's hull design vs. ballast. Some keels (winged) are treacherous on a tall wave where others will slide down the side of a swell with ease allowing the boat to stay more up right. Ballast, lower in the water does create a lower COG but then again if it has a full keel the ... catamaran gulet motorboat riverboat sailboat trimaran yacht