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Old 07-15-2010
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Quote:
Originally posted by Jeff_H
.... I would not say that generically fin keel boats are either safer or more dangerous than longer keel boats when lying abeam to large waves.
but Jeff, in another post
(What is the keel contribution in capsizing.
you said that "... when you have a deep draft keel that is short fore and aft, there is a tendency of that keel to stall as the water is moving closer to perpendicular to the keel. When the keel stalls, it generates smaller sideward resistance relative to its area .... the tendency of modern deep fin keels to stall reduces the impact of surface sheer and so reduces the tendency for surface sheer to rapidly heel the boat. As a result, even if shallower than a modern fin with bulb, a full keel or lower aspect ratio keel could actually have greater tendency towards a surface sheer induced capsize."

As I understand, while in breaking waves there are to cases in which the shape of the keel is to be considered:
1 - when you are caught unexpectedly abeam to breaking waves. In this case it is better to be with fin keel since it produces less sheer forces and hence has less tendency to capsize.
2 - when you prepare for the breaking waves by heaving-to with or without a para anchor. In this case the question is whether a fin keel (with low aspect ratio) can properly heave-to and whether it produces the same "magical" slick that protects from the breaking waves.

If the conclusion is that fin keels are positive in case 2 then one can conclude that fin keel is safer in breaking waves.
If the conclusion is that fin keels behave less positive in case 2 then the question is what to prefer, full keel which better in case 2 but worse in case 1 or fin keel which is good in case 1 and worse in case 2.

Shai.
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