# "DSS" Keel

Discussion in 'Sailboats' started by kvsgkvng, Apr 19, 2012.

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### kvsgkvngSenior Member

I believe here is a simple device combining "DSS" foil and a keel. I think it should work fine. I am sure it is not more complex compared to two DSS foils at each side of the hull. I wonder if it was already done, because it is pretty simple concept. If not, then I would be proud to be the first one!
Cheers, kvsgkvng.

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• ###### DSS-Keel.png
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### philSweetSenior Member

If the keel is torquing the way you have shown, why is the boat heeled over? You first need to get the boat moving in the desired direction with a balance of forces. The DSS works because it operates 90 degrees out of plane to the keel. In practice, many keels have tabs that produce a biased lifting surface, but they are used to lift the opposite way to what you have shown in order to reduce the hull's leeway. You have to balance the forces and the torques to sail a boat. you are ignoring the forces.

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DSS and a keel foil-two different jobs

K, DSS works to generate vertical lift by using a foil that is deployed to leeward. The distance of the center of lift of the foil to the center of buoyancy of the boat is the Righting Arm(RA-f) of the foil. The amount of lift on the foil times the RA of the foil is the Righting Moment(RM-f) generated by the foil. The foil is optimum when generally parallel to the waters surface and about one chord length(of the foil) below the surface.
A keel foil is tasked with resisting leeway and does this by creating "lift" force opposite to leeway. On boats with fixed keels this happens with the whole boat moving slightly sideways so the keel foil has an "angle of attack" that allows it to develop enough lift to prevent most leeway that would result without a keel foil(or daggerboard or centerboard or leeboard).
Over the years keels(or gybing boards) have been designed to rotate the leading edge to windward relative to the centerline of the boat and the theory here is that then the hull doesn't have to move sideways to allow the keel foil to have an angle of attack and supposedly drag is reduced since the hull is not moving sideways.
A DSS foil produces lift that acts nominally vertically; a keel foil produces lift that acts nominally horizontally to resist the horizontal force of the wind on the sail. The two foils act 90 degrees differently.
A boat heels because of the force on the sail pushing to leeward and the force on the keel foil pushing to windward.
Now, if you turned the rotating keel so that the leading edge was to leeward of the centerline of the boat most of the resistance to leeway being generated by the keel foil would be lost-it would be a very bad idea.
Hope this helps a bit.....

click on image for best detail:

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• ###### DSS illustration-2 plus keel.jpg
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