centerboard weight?

[jimnmad]

I'm building a centerboard using 3/4" plywood. I'm going to use lead shot mixed in epoxy as a counterweight. Any ideas about how much weight would be needed to keep it submerged? The board is about 46"X16"X3/4". Also,the plans say to cut a slot 1 1/4" for a centerboard 7/8" thick. If I fiberglass the centerboard (3/4") how much thickness will it add?

[Tom Lathrop]

As a rough estimate, your board comprises about 1/3 cubic foot volume and displaces 20lbs. If made of wood of average density, say 32lb/cu ft, it weighs 10lbs. Therefore for neutral buoyancy it needs 10lbs of lead. Other things enter in like the position of the pivot pin and amount above the waterline when the board is down but if you put in a bit more than 10lbs you will be close. The easy way is to build the board and see how much weight is needed to sink it.

3/8" is a lot of slop to begin with and the glass sheath will not be a problem.

[Sailing-Randy]

jimnmad
I looked at the same problem you are facing and decided I wanted some extra stability. So I drilled several 2" holes and a few 3/4" so the lead would connect from one side to the other. Then I built a mold around the centerboard concentrating the weight on the forward lower point and made it 1/8" thicker than the board. I ended up adding about 38 pounds of weight. I planed the edges to taper into the board edges and fiberglassed over the top. It turned out well. The boat is VERY stable. I had made a winch out of an electric fence tigthener ($2 at the lumber yard) to raise and lower.

Contact me for any other questions if this seems like what you want.
Randy

[Chris Coose]

I rebuilt my 4'x3'x 1" teak CB last year and found the lead weight to be about 5 or 6 #s.
I'd rather have a sinker than a floater.
I used stainless rather than monel to replace the lifting cable. Bad move.