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What is a Sailboat Capsize Ratio and how to measure it

Aug 05, 2020

less than a min

  • What is a Sailboat Capsize Ratio and how to measure it

    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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