Daggerboard

A daggerboard (not to be confused with dagger boards the wooden fascia panels in canopy roofs) is a retractable centreboard used by various sailing craft. While other types of centreboard may pivot to retract, a daggerboard slides in a casing. The shape of the daggerboard converts the forward motion into a windward lift, countering the leeward push of the sail. The theoretical centre of lateral resistance is on the trailing edge of the daggerboard.

A daggerboard is a removable vertical keel that is inserted through a "trunk" in the center of a vessel's hull, usually amidships. Daggerboards are usually found in small sailing craft such as day sailers, which are easily handled by a single person. Daggerboards are not usually ballasted but are locked in place by a clip or pin. Unlike a centreboard, which can be set at different angles to the hull of the boat, daggerboards are generally limited to a single perpendicular position relative to the hull. If a daggerboard is located off center, it is called a leeboard or a bilgeboard.

The characteristic which differentiates daggerboards from other centerboards and swingkeels is that daggerboards are easily removable, even when the boat is under way. Centerboards and swingkeels, common alternatives to fixed keels, can pivot up and down but are fixed to the hull. The freedom of motion of dagger- and centerboards allows them to swing or slide up into the hull of the boat, which is advantageous when sailing in shallow waters. The pivoting centerboard or swingkeel can swing up when it strikes an object which helps prevents the sort of damage to which fixed keels or daggerboards are subject. Daggerboards can be raised and lowered as needed but will generally be damaged if not retracted before impact with the bottom or with floating objects.

Many small sailboats use a daggerboard instead of a fixed keel. This allows these boats to be more easily moved on trailers, sailed in shallow waters, and easily beached. Daggerboards also afford an opportunity to reduce drag when racing because they can be retracted when not needed (i.e. when sailing downwind or in very light winds).

Daggerboards are often made of wood; the problem with wood is that wood rots over time. Alternate materials for daggerboards are metal (aluminum/steel) and fiberglass. A daggerboard boat can be costly to manufacture. If not well-made, the daggerboard will transfer vibrations from the trunk through the hull.

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Wikipedia