I bought a decent power planer and cut it down in 30 minutes. It is only
20% heavier than the mahogany board, when it should be 40% heavier, so
obviously I made it a bit thinner than I intended; but since oak is 50%
stronger than mahogany, that should not matter.

Still don't know if it actually fits, as the boat is 30 miles away with no
electricity.