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post #76 of Old 03-12-2012
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Re: Full or fin keel?

Originally Posted by newbee View Post
We have been given the opportunity to modify the full keel of a 38 ft Sabre we are in love with to a bulb keel by Mars metal. What would the consequences be? We would be choosing this option because we are very inexperienced sailors looking to learn on our liveaboard. The modification would take 1 1/2 feet off of a 6'6" keel and allow us coastal cruising and maybe a trip south.

If I were you, I would talk to Sabre. The new Sabres show a wing keel for a shoal. Probably a smaller wing though. Not sure about the year of your boat, but the Sabres appear to be a great example of a typical American cruising design. A lot of keel weight, good solid hull.

No doubt anyone can design a bulb keel to create the same righting moment as your existing keel. Unfortuneately, such a keel only adds drag with no hydrodynamic benefit. You will clearly lose some pointing with the bulb. If you want to do something useful with the bulb mass, reshape it to a wing.

My feelings are that a good wing design needs considerable area to gain some hydrodynamic benefit. The benefit to gain is the same or increasing resistance to leway movement with heeling. And possibly some benefit to resistance to vertical moment.

The problems I see with adding a wing to the bottom of an existing shortened keel deals with vertical forces. Movement of the hull vertically creates large forces on the keel-wing joint.

The wing keel is unique in that it can create large resistance to vertical moment. Like a huge rocker stopper. It resists downward movement (same as the hull). And more interestingly enough, it resists upward movement unlike any other keel design.

Again, I would contact Sabre.

Last edited by BryceGTX; 03-12-2012 at 02:03 AM.
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