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
What Is Capsize Ratio?
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.
How To Calculate Capsize Ratio
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.
Capsize Ratio Calculator
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.
