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62:, as they are known informally, operate in relatively shallow water, since they must rest on the sea floor. Other floating vessel types are used in deeper water depths. The term
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into the first semi submersible drilling unit for operation in the Gulf of Mexico when it was found to have good stability and motions whilst being towed at a partial draught.
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The
Evolution of Offshore Mobile Drilling Units, Richard J. Howe, Esso Production Research Company, Drilling and Production Practice, 1966, American Petroleum Institute 66-120
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Once on the location, the pontoon structure is slowly flooded until it rests securely on its anchors, of which there are usually two per corner.
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After the well is drilled, the water is pumped out of the buoyancy tanks and the vessel is re-floated and towed to the next location.
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The operating deck is elevated 100 feet above the pontoons on large steel columns to provide clearance above the waves.
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Technology
Pioneers - Drilling Semi-submersible Rigs, Ocean Energy Center :
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By 1958, the number of submersible drilling rigs had increased to around 30.
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Alden J. Laborde designed and constructed the first purpose-built V-shaped
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design that can be floated to location and lowered onto the sea floor for
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In 1961, Shell Oil successfully converted an existing submersible rig
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was 160 feet by 85 feet, and could work in 20 feet water depth.
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Vessel floated to site and lowered onto the seabed for drilling
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http://www.oceanstaroec.com/fame/2000/semisubmersible.htm
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The first offshore mobile drilling platform was the
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141:30 December
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70:Evolution
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19:A
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