Centerboard vs. Bilge Keel - Framing and Reinforcement

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tpelle
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Joined: Fri September 25th, 2009, 3:29 pm
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Centerboard vs. Bilge Keel - Framing and Reinforcement

Postby tpelle » Mon November 15th, 2010, 4:31 pm

Assume a plywood planking on frame hard chine (v-bottom) small sailing boat - something in the 16-foot LOD range. If such a boat were originally designed for a centerboard, and during construction one wanted to install bilge keels instead, what sort of reinforcing framing would have to be installed?

Considering that, when trailering, for instance, or when drying out, the entire weight of the boat, crew, and gear and provisions would be on the bilge keels, and since bilge keels tend to be mounted at an angle from vertical, there would be a "levering" moment at the point where the bilge keel attaches. Especially when trailering it would also have to handle the acceleration/deceleration of the trailer passing over bumps in the road as well.

I expect that one would have to add extra "keel timbers" to the bottom framing near the chine to spread the load over a wider area of the framing, and to provide some "beef" for each bilge keel to bolt to. Would one have to add extra frames as well?

I am posing the question here as the builders of YM Seniors seem to have wide experience with bilge keels.
"Ignoranti quem portum petat, nullus suus ventus est." ("If one does not know to which port one is sailing, no wind is favourable.") -- Seneca the Younger, c. 3BC-65AD

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Fiddler's Green
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Re: Centerboard vs. Bilge Keel - Framing and Reinforcement

Postby Fiddler's Green » Fri November 19th, 2010, 5:53 pm

Yes, you are correct, the bilge keels create a lot of stress and must be backed with large timbers that span several frames and thus spread the load. The Eventide I have uses exactly the same principle and the bilge keel timbers extend from the fore cabin to the cockpit.

If you have a CD of the drawings you will see they are visible on the Senior and all the drawings of boats that include bilge keels.

Regards,
John
Proud owner and builder of 'Fiddler's Green'


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