This 1984 cover depicts the world’s first full-scale tension leg platform. Located in the North Sea, 260 miles off the Scottish coast, above the Hutton oilfield, it was anchored to the seabed in 485ft deep waters by 16 steel moorings.
The floating structure could swing on either side of its foundation like an inverted pendulum up to 68 feet, eliminating vertical movement and revolutionizing deepwater oil and gas extraction.
Her 300-foot by 300-foot base featured pontoons supporting six 200-foot-high columns built in dry dock, with a 26,000-ton hull and 19,000-ton steel deck 250 feet by 243 feet. Developer Conoco UK Ltd. worked at Bechtel Great Britain Ltd.; Brown & Root (UK) Ltd., and British naval architect Vickers Offshore Ltd. to design the floating vessel and foundations.
Each of the ties (also known as tendons) consisted of a 106-ton rope of 17 specially designed 10-inch-diameter steel tubes threaded together. Each tendon had a ball joint at the top and bottom, which had to carry loads of up to 3,100 tons.
The lower ball joints attached connectors that incorporated hydraulic rams, which forced fluid up and down the 3-inch-diameter core of the tendons. Murdoch Machine and Engineering Co., a subsidiary of Lockheed Aircraft Corp., employed by Vickers, designed the tendons using technology developed by Lockheed for rotating pinions in space vehicles.
The 62,000-ton platform, which accommodated up to 100 crew, operated until 2001. The upper parts were purchased by a Gazprom subsidiary and installed on a new platform in the Barents Sea. The helmet was decommissioned in Scotland.
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