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01 December 2015

Mammoet completes offshore jacket project

Ingleside, Texas - Mammoet announces the successful completion of the Coelacanth Project for the third largest offshore jacket to operate in the Gulf of Mexico. 

Mammoet was contracted by Gulf Marine Fabricators in January 2014 to roll-up the jacket’s massive panels and transport the jacket to the barge that would deliver it to its final destination. Mammoet completed the third and final phase of the project, transporting the jacket to the barge, on October 9th, 2015. The 30,000 ton jacket was pulled by strand jacks 1,450 feet (442m) from the fabrication location to the barge. The transport took fifty-nine continuous hours from beginning to end.

The jacket is a huge structure that will ultimately stand over 1,200 feet (366 meters) tall and will weigh 60 million pounds (30,000 tons). The panels themselves are 387 feet high (118 meters) and 374 feet (114 meters) wide. Mammoet and Gulf Marine took an innovative approach to assemble the large structure.

Traditionally, a jacket is ‘stick-built’ - constructed piece-by-piece - until it is built up to its full height. This requires construction workers to carry out their tasks at height. An alternative method is to use prefabricated panels which are constructed at ground level and then put in place in a roll-up operation carried out by cranes. The use of prefabricated panels has the advantage of reducing the need to work at height, resulting in improved safety for construction workers. It also means construction on the panels can take place simultaneously, saving time.

For the Walter jacket, with its large dimensions and heavy panels, a large number of specialized heavy lifting cranes would have been required to perform the roll-up operation. Gulf Marine Fabricators investigated the possibility of an alternative approach and, working jointly with Mammoet, developed a method using strand jacks. This approach reduced the need for multiple high-strength cranes on site, while capitalizing on the safety benefits of using prefabricated panels.

Using this alternative method, the panels were ‘rolled’ from a horizontal position to the required vertical placement. This roll-up procedure was carried out on two panels at a time, requiring continuous precision control of all the strand jacks to minimize deflection in the panels. A customized software system was developed to ensure this level of control and synchronize the operation of the strand jacks. Smaller cranes were used to assist the strand jacks until the panels had reached a 30 degree angle. From this point the strand jacks could lift the panels to the point where they were welded to the main structure.

The roll-up was carried out in two phases. In the first phase, Mammoet employed 12 strand jacks to move the panels in the middle section into place. In phase two, Mammoet used 18 strand jacks to maneuver the panels on the lower section. The final phase of the project for Mammoet was transporting and loading the jacket on to the barge. The offloading of the jacket and platform installation was completed successfully.

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