A crane vessel, crane ship or floating crane is a ship with a crane specialized in lifting heavy loads. The largest crane vessels are used for offshore construction. Conventional monohulls are used, but the largest crane vessels are often catamaran or semi-submersible types as they have increased stability. On a sheerleg crane, the crane is fixed and cannot rotate, and the vessel therefore is manoeuvered to place loads.
In medieval Europe, crane vessels which could be flexibly deployed in the whole port basin were introduced as early as the 14th century.
During the age of sail, the sheer hulk was used extensively as a floating crane for tasks that required heavy lift. At the time, the heaviest single components of ships were the main masts, and sheer hulks were essential for removing and replacing them, but they were also used for other purposes.
In 1920, the 1898-built battleship USS Kearsarge (BB-5) was converted to a crane ship when a crane with a capacity of 250 tons was installed. Later it was renamed Crane Ship No. 1. It was used, amongst other things, to place guns and other heavy items on battle ships under construction. Another remarkable feat was the raising of the USS Squalus (SS-192) in 1939.