Mirage Field Multi-Column Deep Draft Floating Platform: Graving Dock Construction and Hull Fabrication

Abstract

Abstract In the fourth quarter of 2006 the first prototype multi-column deep draft floating platform (DDFP) was contracted for fabrication. The hull is a patented deep-draft floating production system with three vertical columns arranged in a triangular shape. The hull looks like a semisubmersible but behaves like a spar in terms of stability and dynamic response to waves. With the development on the " fast track??, construction began while the details of the hull were still being designed. This presented numerous opportunities for the project team to overcome. One of the initial problems that needed to be solved was how to launch hull into the water. The project team decided to construct a graving dock, the largest of its kind on the U.S. Gulf Coast. The graving dock construction began in April 2007 and was complete in February 2008. In January 2007 hull fabrication began. The hull was fabricated in smaller subassemblies that included the upper column, lower column, pontoons, lower raft, and the access trunks. These sections were fabricated in various locations using jigs and panel lines. The smaller subassemblies were then joined to form larger subsections. As the subsections were completed, they were assembled in the graving dock. Each section lift weighed between 450 and 3,000 short tons and were lifted using various combinations of spreader bars, crawler cranes, lifting towers and strand jacks. After fabrication was completed, the graving dock was flooded, the front wall of the dock was removed and the hull was ready for tow.