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post #504 of Old 10-02-2012
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Re: Full or fin keel?

To ChucklesR question about a late 80's 3ft' stub keel with a wing: First of all, the Australians created quite a stir with their wing keel in the America's Cup in the 80's and it seemed to create a marketing angle for some boatbuilders. There obviously was some merit, but there are several factors at play when translated to the recreational market.

First of all, the wing keel provides an end plate for the primary keel to reduce tip vortices--for the same reason you see winglets on the later versions of commercial jets--to reduce drag. Also, adding the wing shape produces a fatter (i.e., heavier) "bulb" to provide more of a righting moment for a given keel length.

That said, you may notice that the more efficient racing keels are like glider wings: deep, high aspect foils. The downside is the deep draft required to pursue this approach.

But, getting back to ChucklesR's Irwin, it's all about a real world compromise. A short stub keel is not going to provide the lift of a longer, high aspect foil, but, by adding the wing (for added ballast) it can offer reduced draft.

Oh, by the way, a full keel is the antithesis of an efficient, high aspect keel, for those who care to think about keel compromises. You might look to aircraft design for a reference point. The only aircraft I can think of with low aspect wings are "wing-in-ground" (WIG) craft, like the one built by Merrifield Roberts in Rhode Island about 20 years ago or the huge, "Caspian Sea Monsters" built by the Soviets several decades ago. That said, I am not a hydrodynamicist or naval architect/boatbuilder, so you can take my comments with a grain of salt.
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