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Old 01-12-2010, 11:29   #1
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Can anyone help me understand how the following calculations are arrived at and their signifigance?

Capsize ratio
Sail area to displacement
Displacement to LWL
LWL to beam
Pounds/inch

Thanks in advance
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Old 01-12-2010, 11:44   #2
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You might want to take a look at Ted Brewer's primer on yacht design--that would answer most of your questions and then some:

Ted Brewer Yacht Design

This will also answer some of your questions:

Ratio Formulas
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Old 01-12-2010, 12:26   #3
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Quote:
Originally Posted by Bluefuss View Post
Can anyone help me understand how the following calculations are arrived at and their signifigance?

Capsize ratio
Sail area to displacement
Displacement to LWL
LWL to beam
Pounds/inch

Thanks in advance
Capsize ratio is fairly insignificant in that it really doesn't predict much about a boat's stability. It's mostly just something invented by the skinny-boat guys to make themselves seem superior to the fat-boat guys. Knowledgeable cruisers tend to ignore this formula.

Sail area to displacement is a major predictor of a boat's power. The higher the number, the better a boat will accelerate. Cruisers don't want too high a number, because that would indicate a tender vessel. Some cruisers claim they don't mind going slow, so a low SA/D ration is seen to be desirable. These people are delusional, of course.

Displacement/LWL will tell allow you to compare the heaviness of Boat A relative to Boat B. We could argue forever what a good range would be for a cruising boat, as opposed to a racer/cruiser, et cetera.

LWL/Beam gives you a hint as to the boat's profile. This is common sense. Beam is fairly insignificant until you consider the boat's length, right? A fourteen-foot beam an a 35 footer would be an awfully stubby boat, but a 55 footer with that same beam would seem to be fairly sleek.

Pounds/inch is an indication of how much weight a boat can handle before sinking an inch of waterline. Far more cruisers and liveaboards should be paying attention to this number than they usually do. The reason a lot of cruisers sail like dogs is because they're so far down on their waterline. Again, the delusional cruisers among us will claim that they don't mind going slow.

I should probably have put a smiley face after each instance of the word "delusional" above. Or maybe one of those little popcorn eaters.
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