Due to unrestricted ocean operations of a drillship, the importance of its transit speed is increasing in the viewpoint of reducing the downtime of offshore operations to a minimum. The open moonpool in a drillship induces additional drag when the ship is in transit. As an unfavorable moonpool design may cause the excessive drag, various ways to reduce the drag have been studied in theoretical and experimental methods. In this paper, an efficient way to reduce the drag due to moonpool and consequently increase the transit speed has been proposed. The reduction of moonpool drag has been focused as the moonpool drag is around 30% of total resistance of the drillship. A simple and efficient shape to mitigate excessive water motion inside the moonpool during drillship's transit is developed and verified through a series of model tests at SSMB (Samsung Ship Model Basin). Based on the observation during the model tests, it is found that a remarkable drag reduction can be achieved by the devised moonpool shape. Thus, it is concluded that more economical operation of a drillship such as the lower fuel consumption and increase of working time can be expected.

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