I bought a good 3.5" power planer and cut it down in 30 minutes. I used a
belt sander to smooth the lines out, and a router table to radius the front
and back.

Tomorrow I will see if it fits. (the boat is 30 miles away, with no
electricity) Since oak is 40% heavier than mahogany and the finished oak
board is only 20% heavier than the mahogany board, I must have made it
thinner than I intended; but since oak is also 50% stronger than mahogany,
that shouldn't matter.

It may not be a perfect mathematical airfoil, but it is pretty close to the
(unpracticed) eye.