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post #581 of Old 01-09-2013
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Re: Full or fin keel?

Originally Posted by blt2ski View Post
Do not remember which number, be it capsize or comfort ratio, but was not one of them "hood" a naval architect that came up with that ratio. Later said it was good, but at the end of the day with some of the newer designs not as useful as with past designs. Not saying that that ratio should be thrown out per say, as it favors longer/skinnier designs vs some of the fatter hulled designs of today. Rather apparent that hull design will potentially make or break a design depending upon useage as to if it will or will not work for the end user. Not just fin vs full vs bilge vs CB or some combo there of!

The more I type, I believe it is the motion comfort ratio number. Even short will come out on the lower side of things than width. As a 30'L 10' wide boat will come out with a worst number than a 60' x 20', even tho the length.width ratio is equal. I am also recalling disp being part, maybe that needs to be equally doubled to get the same ratio, where is going up double in length, usually (typically) quadruples or equal the disp of the boat. That would be an interesting plug in numbers to see what or if one can get different equal length and beam to equal....

Hi Marty,

Many years ago, having already an interest in boat design I bought a more complete and complicated performance boat calculator the kind wolfenzee used to compare those boats and also many years ago I trough it to garbage.

That type of calculators only works with old boats and even so they have to have a similar hull shape and type of keel. The Capsize ratio ratio is particularly misleading and the comfort ratio is pretty meaningless. Jeff posted a thread about motion comfort in modern boats and posted in it also a very good article about that.

Modern Hull forms and Motion Comfort

Regarding motion capsize ratio probably the best discussion about it is on other forum but the results from the discussion are quite clear. I do not even feel the necessity to discuss that on sailnet. I guess that almost all know that the ratio does not make any sense when applied to modern hulls and by modern I am talking about 35 year's old hulls, at least the good ones.

Capsize Ratio's - Cruisers & Sailing Forums



Last edited by PCP; 01-09-2013 at 02:14 PM.
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