A wing keel is a type of sailboat keel designed to improve stability and performance. It features a flat, horizontal wing shape at the bottom, which increases lift and reduces drag when the boat is sailing. This design allows for better upwind performance and helps the boat remain upright in strong winds. The wing keel was popularized by the racing yacht Australia II, which won the America's Cup in 1983. Its innovative design challenged traditional keel shapes and demonstrated how engineering advancements could enhance sailing capabilities, influencing future yacht designs.