Originally Posted by Limpet
Forgot I started this thread long ago.
Aren't most dagger board shapes symmetrical...in which case there is no lift
because the water
flowing over the surfaces on both sides is moving at the same speed.
An airplane wing provides lift
because the air travels faster over the longer top surface thus creating a low pressure on top surface of the wing relative to the pressure below the wing.
This makes for the most efficient shape but it is the angle of attack that determines the amount of lift. You could take a sheet of plywood
, give it an angle of attack and it would produce lift, no flat and rounded side necessary.
A rounded backside helps to preserve the laminar flow, without it there is a greater inclination for there to be a vortice in the same area if it were a flat backside. A laminar flow creates the greatest pressure differential, for the amount of drag, between the low pressure and high pressure sides of the foil.
Originally Posted by ElGatoGordo
Not sure what you're asking. I haven't heard of asymmetrical boards. It would only generate lift on one tack...sounds like a pain to me.
An asymetrical board with the high pressure side being on the rounded side would still generate lift, otherwise an airplane would never be able to fly inverted. Doing it this way is just less efficient with there being a lot more drag.