A sliding centreboard of wood or metal. It can be raised or lowered inside a case through a slot in the keel of a shallow-draught boat, to increase the effective draught and so reduce leeway when sailing close hauled. It was one of the earliest types of sliding keel and originally used by the Chinese in some of their river junks. It is so called because it is generally narrow in proportion to its length and, not being pivoted like a true centreboard, slides down from its case like a dagger from a sheath.
Subjects: Maritime History.