Increased deck space on offshore structures often comes at a premium but designers of a recent semisubmersible for Transocean/Sedco-Forex found a novel solution. They relocated the engines, generators and mud tanks into the pontoons, which lowered the center of gravity, improving stability and increasing the speed at which operators can drill.

Issues that had to be overcome to make this project a reality included concerns about how regulatory guidelines applied to this new design, particularly the provision of necessary electrical power, piping, engine exhaust and fire protection for a system located below the waterline and facing possible water ingress. With the Cajun Express, the concept of moving weight down into the pontoons meant adding equipment not usually associated with a conventional rig and not specifically covered by regulatory statutes. Huge exhaust trunks are needed to ventilate from the pontoons to the deck level and the derrick itself is four times as large as a conventional derrick, running the breadth of the deck. Additionally, with the new design came new strength and fatigue considerations.

When delivered, the unit will be ABS classed as self-propelled with the propulsion from the dynamic positioning thrusters. It is capable of dynamic positioning during drilling operations in deep water. The Cajun Express will receive ABS’ highest-class designation for a self-propelled semisubmersible drilling unit, +A1 Column Stabilized Drilling Unit +AMS +DPS3.

More information: ABS