Leeboard

A leeboard is a flat board fixed to the side of a flat-bottomed sailing vessel and lowered into the water to resist sideways drift, functioning like a centerboard except that leeboards are fitted in pairs, one on each side of the hull, and only the board on the leeward side is lowered at a time since the other lifts clear of the water as the boat heels under the wind. The arrangement let shallow-draft working boats sail waters no fixed-keel vessel could enter, while leaving the cargo hold and interior free of the trunk a centerboard needs, and it was simpler to build than a large centerboard. Leeboards originated in China by at least the eighth century, recorded on warships said to resist being driven sideways or overturned in a storm, and the technology reached Europe around 1570 through Portuguese and Dutch mariners who adapted it from Chinese vessels; from then on, Dutch barges, Thames sailing barges and American gundalows all carried leeboards for their combination of shallow draft and open cargo space.