The Troll A platform is an offshore natural gas platform in the Troll gas field off the west coast of Norway. At 1.2 million ton ballasted under tow, 472 meters high, with underwater concrete structure at 369 meters, and dry weight of 656,000 tons, the Troll A platform is a majestic piece of design and construction. Not only is Troll A among the largest and most complex engineering projects in history, it is the largest object ever to be moved by man across the surface of the Earth. The platform was a televised sensation when it was towed into the North Sea in 1996, where it is now operated by Statoil.
Normally a platform’s legs are transported on their side and then – supported by flotation devices – are dropped into place. In the case of Troll A, however, the whole platform was assembled in one location, and then floated out to sea. The Troll platform was towed over 200 kilometers from Vats, in the northern part of Rogaland, to the Troll field, 80 kilometers north-west of Bergen. The tow took seven days.
The platform stands on the sea floor 303 meters below the surface of the sea and one of the concrete cylindrical legs has an elevator that takes over nine minutes to travel from the platform above the waves to the sea floor. The walls of Troll A’s legs are over 1 meter thick made of steel reinforced concrete formed in one continuous pour. The four legs are joined by a “Chord shortener”, a reinforced concrete box interconnecting the legs, but which has the designed function of damping out unwanted potentially destructive wave-leg resonances. Each leg is also sub-divided along its length into compartments a third of the way from each end which act as independent water-tight compartments. The legs use groups of six 40 meters tallvacuum-anchors holding it fixed in the mud of the sea floor.
In 1996 the platform set the Guinness World Record for ‘largest offshore gas platform’. The title now belongs to the Petronius Platform in the Gulf of Mexico which stands 2,000 feet (610 m) above the ocean floor.