leeboard

/ˈliːbɔːrd/
noun
  1. A flat board attached to the side of a boat that can be lowered into the water to reduce sideways drift.
    • He adjusted the leeboard to improve the boat's balance while tacking.
    • The sailor lowered the leeboard to keep the boat from sliding sideways in the wind.
    • Small sailboats often use a leeboard instead of a heavy keel.