Sevan Driller (Credit: COSCO Nantong Shipyard/Sevan Marine).


“Te top of the drilling derrick of the Sevan Driller seen here at night (Credit: COSCO Nantong Shipyard/Sevan Marine).


whenever the ship moves, the effect of wind direction and current on different parts of the ship hull needs to be considered because a drill ship has a longer body. A disadvantage of cylindrical and square


rigs when compared with rectangular drill ships is that they move slower. “But a drilling unit is not expected to move too oſten,” Xu added. Also, the heeling (vertical movement)


of the units in the sea is more obvious for cylindrical or square rigs than for drill ships.


Innovations during construction Coming up with new ideas takes imagination and ingenuity, making an idea work requires no less creativity.


Lacking a big enough dry dock for the


construction of the Sevan Driller, COSCO has built a 20,000dwt launch barge as the construction platform for the project. “Using this method has made dimension control and liſting more difficult. It requires a lot more calculation to be done than building the rig in a dock,” said Xu. As the launch barge is afloat with motion,


the stability of the body of the rig and the parts to be assembled and installed needs to be carefully calculated, he explained. Te company has gained a patent for this shipbuilding technique in China. The shipyard also had to borrow a


4000tonnes floating crane from Shanghai Zhenhua Heavy Industry Co (ZPMC) to finish the liſting procedure.


Offshore Marine Technology 3rd Quarter 2010


Sevan Driller is 136m above baseline and located in the centre of the rig, which is 45m from the side, the crane should have the capacity to lift 260tonnes to 136m above waterline and the required outreach is 45m. We have studied different types of floating cranes and found that only the 4000tonnes crane from Shanghai Zhenhua Heavy Industry Co (ZPMC) can meet all the liſting criteria,” said Xu. COSCO has achieved 100% precision


in the construction of blocks of hull while building the Sevan Driller, explained Xu. He explained that many Chinese shipyards are not able to build ship blocks precisely into the shapes and size required in the block fabrication process and need to further cut blocks into their exact required shapes and sizes in the shipway before assembly. Despite the cylindrical shape of the hull


making it more difficult to achieve 100% precision, COSCO has managed to build blocks into their required shapes and sizes, said Xu. “Te shipyard had to assemble 16 blocks to form the cylindrical hull of the rig which required a high level of skill in block fabrication.” Sevan Brasil is scheduled to be delivered in the first quarter of 2012. OMT


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In-depth


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