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post #522 of Old 10-03-2012
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Re: Full or fin keel?

Originally Posted by PCP View Post
A sailboat is not a motorboat that bobs around in waves and in bad weather will be strongly “tied” to a side by the force of wind on its sails. You don’t need a book to know this; you have only to experience it.


A typical powerboat is considerably stiffer than a sailboat of similar size. And that is exactly why they are worse on rough water than a good rough water sail boat. Again, common knowledge.

Just so everyone knows, the stiffness of a boat is invariably determined primarly by the hull. A wider hull invariably creates a stiffer boat. Adding weight adds some stiffness, but nothing to that which can be had by modifying the hull. A wide flat power boat creates exactly such a stiff boat. And given that it carries its width longer than a sailboat, it inherently has more stiffness. The power boat has the problem that its CG is invariably above the waterline. This causes the CG to actually create a heeling moment. Which explains why some power boats can appear less stiff.

The stiffest sailboats are catamarans. They carry the beam to extreme resulting in a huge hull moment. And as we know, cats do not heel like monohulls. As a result can be very fast.

You seem to be confusing performance with rough water capability and those with experience know that rough water boats are different from performance boats. As far as I am concerned, this is widely held common knowledge.

The force of the wind on the sail has nothing to do with stiffness of the hull. I suggest you pick up a book and convince yourself. That is not to say a sail does not help stabilize the boat.

Last edited by BryceGTX; 10-04-2012 at 12:06 AM.
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