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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.
History
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 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 other battleships under construction. Another remarkable feat was the raising of the submarine USS Squalus in 1939.
In 1942, the crane ships a.k.a. "Heavy Lift Ships" SS Empire Elgar (PQ16), SS Empire Bard (PQ15), and SS Empire Purcell (PQ16) were sent to the Russian Arctic ports of Archangel, Murmansk and Molotovsk (since renamed Sererodvinsk). Their role was to enable the unloading of the Arctic convoys where port installations were either destroyed by German bombers or were non existent (as at Bakaritsa quay Archangel).
In 1949, J. Ray McDermott had Derrick Barge Four built, a barge that was outfitted with a revolving crane capable of lifting 150 tons. The arrival of this type of vessel changed the direction of the offshore construction industry. Instead of constructing oil platforms in parts, jackets and decks could be built onshore as modules. For use in the shallow part of the Gulf of Mexico, the cradle of the offshore industry, these barges sufficed.
In 1963, Heerema converted a Norwegian tanker, Sunnaas, into a crane vessel with a capacity of 300 tons, the first one in the offshore industry that was ship-shaped. It was renamed Global Adventurer. This type of crane vessel was better adapted to the harsh environment of the North Sea.
In 1978, Heerema had two semi-submersible crane vessels built, Hermod and Balder, each with one 2,000 ton and one 3,000 ton crane. Later both were upgraded to a higher capacity. This type of crane vessel was much less sensitive to sea swell, so that it was possible to operate on the North Sea during the winter months. The high stability also allowed for heavier lifts than was possible with a monohull. The larger capacity of the cranes reduced the installation time of a platform from a whole season to a few weeks. Inspired by this success similar vessels were built. In 1985 DB-102 was launched for McDermott, with two cranes with a capacity of 6,000 tons each. Micoperi had M7000 built in 1986 with two cranes of 7,000 tons each.
However, due to a oil glut in the mid 1980s, the boom in the offshore industry was over, resulting in collaborations. In 1988, a joint venture between Heerema and McDermott was formed, HeereMac. In 1990 Micoperi had to apply for bankruptcy. This enabled Saipem – in the beginning of the 1970s a large heavy lift contractor, but only a small player in this field at the end of the 1980s – to take over M7000 in 1995, later renaming it Saipem 7000. In 1997 Heerema took over DB-102 from McDermott after discontinuation of their joint venture. The ship was renamed Thialf and, after an upgrade in 2000 to twice 7,100 tons, it is now the largest crane vessel in the world even if all the world's lifting records belong to Saipem 7000 (12,150t of Sabratha Deck).