Early History
The semi-submersible design was first developed for offshore drilling activities. Bruce Collipp of Shell is regarded as the inventor. But Edward Robert Armstrong may have paved the way with his idea of 'seadrome' landing strips for airplanes in the late 1920s, since his idea involved the same use of columns on ballast tanks below the surface and anchored to the ocean floor by steel cables.
When oil drilling moved into offshore waters, fixed platform rigs and submersible rigs were built, but were limited to shallow waters. When demands for drilling equipment was needed in water depths greater than 100 feet (30 m) in the Gulf of Mexico, the first jackup rigs were built.
The first semisubmersible arrived by accident in 1961. Blue Water Drilling Company owned and operated the four column submersible drilling rig Blue Water Rig No.1 in the Gulf of Mexico for Shell Oil Company. As the pontoons were not sufficiently buoyant to support the weight of the rig and its consumables, it was towed between locations at a draught mid way between the top of the pontoons and the underside of the deck. It was observed that the motions at this draught were very small and Blue Water Drilling and Shell jointly decided that the rig could be operated in the floating mode.
The first purpose built drilling semi-submersible Ocean Driller was launched in 1963. Since then, many semi-submersibles have been purpose-designed for the drilling industry mobile offshore fleet.
The industry quickly accepted the semi-submersible concept and the fleet increased rapidly to 30 units by 1972.
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