Overview
A hulk is a ship that is afloat, but incapable of going to sea. Hulk may be used to describe a ship that has been launched but not completed, an abandoned wreck or shell, or to refer to an old ship that has had its rigging or internal equipment removed, retaining only its buoyant qualities. The word hulk also may be used as a verb: a ship is "hulked" to convert it to a hulk. The verb was also applied to crews of Royal Navy ships in dock, who were sent to the receiving ship for accommodation, or "hulked". Hulks have a variety of uses such as housing, prisons, salvage pontoons, gambling sites, naval training, or cargo storage.
In the age of sail, many hulls served longer as hulks than they did as functional ships. Wooden ships were often hulked when the hull structure became too old and weak to withstand the stresses of sailing.
More recently, ships have been hulked when they become obsolete or when they become uneconomical to operate.
Sheer hulk
A sheer hulk (or shear hulk) was used in shipbuilding and repair as a floating crane in the days of sailing ships, primarily to place the lower masts of a ship under construction or repair. Booms known as sheers were attached to the base of a hulk's lower masts or beam, supported from the top of those masts. Blocks and tackle were then used in such tasks as placing or removing the lower masts of the vessel under construction or repair. These lower masts were the largest and most massive single timbers aboard a ship, and erecting them without the assistance of either a sheer hulk or land-based masting sheer was extremely difficult.
From Wikipedia (CC BY-SA 4.0).