leeboard 
noun
A plank frame fixed to the side of a flat-bottomed boat and let down into the water to reduce drifting to the leeward side.This spacer fills the gap between side and leeboard when board is touching the gunwale and chine log....
- An article on making a leeboard from laminated plywood is available.
- The Chinese widely used leeboards and so I thought of replacing the bilgeboards by leeboards also.