Under a sword is understood in shipbuilding and in the maritime one on dinghies to parallel the direction of travel vertically through the hull pushed plate of steel , wood or FRP for reducing spray drift or to the implementation of the drift in advance . Even catamarans can be equipped with two swords.
In addition to the main type, the central swords , a distinction is made between the side swords (in Ewern and other flat-bottomed ships attached in pairs to the side outboard) and chin swords (two side swords within the hull of the boat); Kielschwerter are the advantages of made up for the sword, and the ballast keel together.
The depth of the sword can usually be adjusted continuously. This makes it easier to maneuver in shallow water and enables higher speeds by pulling up the sword on downwind courses and on downwind courses, as the water resistance is reduced. An adjustable sword is held by a surrounding sword case .
A sword reduces the lateral drift mainly due to the larger area in the lateral plan , at higher speeds but also due to the dynamic buoyancy of the adjacent laminar flow . In contrast to fin keels or ballast swords, a sword does not protect against capsizing due to a lack of mass . However, it dampens the rolling movements through the lateral water resistance and thus stabilizes the boat.
The most common is the folding sword , which is attached at its head end to an axis lying transversely to the direction of travel. The head end itself points in the direction of travel, that is, the sword folds out against the direction of travel. If it hits the ground, the sword can therefore fold back again, which may prevent major damage to the boat. The height of the sword is adjusted with light swords by two lines running in opposite directions (sword halyard and vang). The disadvantage of this construction is the larger space required for the sword case. With ballast swords a rope is sufficient to catch up, which can be translated by a tackle (pulley block) to save energy ; some ballast swords are operated with crank drives or hydraulically.
Another embodiment is the non-rotatably mounted clamping sword or plug-in sword . The height is adjusted by pushing it up or down, while the sword itself is clamped in the sword case due to its special shape. The disadvantage of this construction is the higher stress on the sword at the edges and the position that is not so precisely and permanently adjustable compared to the folding sword. In addition, a fully retrieved sword usually has to be completely removed from the sword case and stowed on deck.