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A leeboard is a movable board that can be lowered at the downwind side of a boat to reduce drag. Known as the lee side, the downwind side is the position of choice for the board because if the ship heels, or tips to the side under the wind, the board will remain submerged. This device acts as a foil to allow boats to go faster and move more smoothly, with less sideways motion and slippage. Such installations are more common on small boats, including those built by hand, rather than larger craft.
The shaping is an important consideration with leeboard design. When lowered into the water, the board needs to reduce resistance, minimize splashing, and avoid trapping water next to the boat. Leeboards are typically slightly curved and their angle is controllable with adjustments on the surface. They must be angled correctly to be effective, as shallow or steep angles can interfere with navigation.
When a leeboard is not in use, the boater can swing it up out of the water and secure it. This can be important when boats travel in shallow water where the trailing board might run aground, or when sailing conditions do not call for the use of a leeboard to stabilize the boat. Some boats have a matched pair of boards, allowing the sailor to control which is lowered, because the leeward side of the ship can change. In others, the board detaches and can be moved back and forth as necessary.
Custom boat orders may include a call for a leeboard, in which case the shipbuilder can determine the needs of the craft and design an appropriate attachment. It is also possible to retrofit to add them to an existing boat. Sailors can ask a shipyard to do this work if they do not feel comfortable with their own installation. Detailed guides on the construction and placement of leedboards are also available, for boaters who feel more confident in their abilities.
This device serves a function very similar to that of the centerboard, also known as the daggerboard. The primary disadvantage to the daggerboard is that space needs to be available in the middle of the boat for times when the sailor wants to retract it. On a small craft, this can eat up valuable space and make the boat much less comfortable for passengers. Leeboards tuck out of the way along the sides of the boat and do not take up room, making them very useful for small craft.