April 11, 2013

Some thoughts about capsize

MOST SAILORS KNOW that the resistance a sailboat offers to being capsized can be measured with the aid of U.S. Sailing’s capsize-screening formula. It is an indication of a boat’s initial stability, that is, her stiffness or resistance to being heeled over. But not all sailors realize that it is not an indication of a boat’s ultimate stability, which is her resistance to remaining completely upside down after having been capsized by a large wave.

It is one of those strange things about naval architecture that a boat that is difficult for the wind to capsize might be vulnerable to remaining upside down if she is capsized by a big breaking wave. A narrow hull with a deep heavy keel will quickly roll upright from a 180-degree capsize, whereas a fat shallow boat will float upside down quite happily for a long time — if she’s not taking on water while she’s inverted.

However, to determine the capsize screening formula, which indicates the initial stiffness of a boat, divide your boat’s displacement in pounds by 64.

Find the cube root of that number.

Take the beam in feet and tenths of a foot, and divide it by the cube root you just worked out.

If the answer is less than 2, your boat is considered relatively safe from capsizing.

But don’t be misled. Even the largest yachts can be turned turtle by a breaking wave with a height equal to 55 percent of their length on deck according to the results of tests carried out by Southampton University in England.

Today’s Thought
As soon as there is life there is danger.
— Emerson, Uncollected Lectures: Public and Private Education

Tact is the ability to shut your mouth before somebody does it for you.

(Drop by every Monday, Wednesday, Friday for a new Mainly about Boats column.)


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