Builders' Forum Archives
Re: lead in daggerboard?
Posted by Steve Miller on Jun 13, 2005
I agree with Joey. Skip the lead and add a length of bungee or even nylon cord/rope over the top of the board. I like having the board float up on downwind legs too as well as when I get close to shore to beach the boat I can just let the board float up. Likewise when launching the boat I find having it up is better.
With lead you will be in the opposite situation looking for a way to hold what is now a guillotine blade up. Much harder.
But if you want to do the lead here is the info on how to calculate how much (from Jim Michalaks Newsletter). Note that if your board is a tapered wing shape you have less wood therefore need less lead:
"The sink weight should be slightly heavier than the buoyancy of the immersed blade. Wood is about half as dense as water, and lead is about 11 times denser than water. It works out that the area of the lead weight should be about 1/16th the area of the immersed blade, or maybe 7 percent of the area to give a slight negative buoyancy. For example, a blade that is 10 inches by 15 inches immersed is 150 square inches. The lead weight could be 150 x .07 = 10.5 square inches, which would be a square 3.24 inches per side. Cut a hole in the blade for the lead to the proper size, preferably toward the tip and toward the trailing edge. Bevel the hole's edges so the lead will lock in place by forming flanges around the blade. Also place some rustproof nails or screws around the interior of the hole to further lock the lead in place. Clamp the blade to a flat metal plate and place it level on the floor.
To figure the weight of the lead required, multiply the area in inches by the thickness in inches and again by .4. In the example, if the example blade is 3/4" thick, the weight of the lead required is 10.5 x .7 x .4 = 3.15 pounds."
In Response to: Re: lead in daggerboard? by J.Schott on Jun 13, 2005