A bilgeboard is a lifting foil used in a sailboat, which resembles a cross between a centerboard and a leeboard.
When sailing, the windward side bilgeboard is retracted into the hull of the boat, so that it produces no drag.
The leeward side foil provides the lift to counter the lateral force of the sail, and converts it into forward motion.
Like a centerboard, the bilgeboard can be used as a recovery platform upon which to stand in the event the dinghy overturns via a capsize or turtle.
The Red Fox is a modern cruising yacht that uses bilgeboards to allow a lifting keel with minimal interference in cabin space.