What every self-respecting, teenage boy can explain to you
about the front wheels of a car, applies identically to leeboards: For optimum performance
the boards must have camber, caster and toe-in.
They are up to 20 percent more effective than a centerboard. It allows for
They never jam. They are easier to maintain and to repair in case of damage.
Just take them off. Their main advantages are that they eliminate the need for a
centerboard box, which in 90 percent of the cases is the cause of leaks, and leave a
roomy, uncluttered cockpit.
The disadvantages are two extra ropes to handle when tacking, and you have to
be (more) careful when docking.
They also require an extra plank above the sheer. The plank must tumble home
to provide the camber for the boards. See figure 9-6A.
The camber is determined by the inclination of the tumbled-home plank
above the gunwales. You could call the angle of the plank a negative flare angle.
In figure 9-6A it is 9.46 degrees. Tangent of the camber angle is 1/6 = 1.666667.
Maximum effect and efficiency are reached when the hull is sailed with
the gunwale on the waterline, or settled on the gunwale. Then, the board is
vertically down. The flat-bottom sails as a V-bottom.
In this position the leeboard is more effective than a centerboard. The lateral
resistance of the centerboard is equal to the vertical arm of the illustrated centerboard
vector, which is equal to the length of the centerboard x cos heeling angle.
The more heeling, the less resistance when it is needed the most.
It explains why leeboards are 15 to 20 percent
shorter than centerboards.
The hole to hang the leeboard is off center for a smooth sliding action. The caster
angle is not too critical. For a small boat, it is not necessary to hollow the
outside of the board. The convex inside will still give a lifting action toward windward.
See figure 9-6B.