A board, or frame of planks, lowered over the side of a vessel to lessen her leeway when closehauled, by giving her greater draught.

a plate or foil that's lowered into the water beside the kayak

A large fan-shaped wooden board fitted at each side of a barge and pivoted at its forward end. When the board on the lee side is lowered it increases the effective draught of the barge and serves to reduce the amount of leeway when sailing close-hauled. It operates in much the same way as the centreplate of a dinghy.