# keel design

Discussion in 'Boat Design' started by max, Oct 13, 2003.

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### maxJunior Member

Hi there,

I´m trying to design a keel for a sailing boat L=16m Displ. 14000 kg. sailarea 140 sqm .
I started with the keel area as shown in L. and E. with 3% of sail area. And I have the possibility to get an idea of the sideforces in different conditions caused by the sails with the help of an vpp software. My question is how I can get the angle of attack for different hull speeds to get the best naca profil for my needs. I know that a lot of parameter depend on each other but I need an idea how to start.

Ciao,

Max

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### Stephen DitmoreSenior Member

Think 2 1/2 degrees when charging along at full speed and 4 deg if going a bit slower because of waves or because you're accellerating out of a tack.

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### maxJunior Member

Thanx a lot for your suggestion ! I will calculate some profiles with these angles.
I also found a nice articel about keel design on the homepage of vacanti yacht design.

ciao max

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### tspeerSenior Member

Since you know the sideforce, you can calculate the angle of attack required. The formulae are in Fig 6.5 of L&E.

For steady state conditions, lift on the keel is approximately equal to the sideforce from the rig, and the angle of attack of the keel is the leeway angle. Set L = sideforce, solve for CL, then solve for alpha.

As a designer, you actually get to pick the leeway angle. You can set it to be anything you want, then size the keel so that it produces the required lift at that leeway.

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