Surendran Sankunny

A moonpool is meant to access the underwater part of hull from onboard ship. Moonpools are openings right through the hull from deck to bottom, allowing equipments, ROVs, etc. to be put into the water at a location on the vessel under permissible ship motion condition. Open moonpools in a drillship are causing additional resistance when the ship is in forward speed. It was shown that the water inside the moonpool started to oscillate at forward speed. The drillship is mainly subjected to two types of motions of water mass inside the column namely, piston mode and sloshing mode. The later mode will be dominant in longer moonpools and piston mode in shorter. The amplitude of water particles inside the moonpool is correlated with the forward speed such that increased forward speed leads to increased amplitudes. The main objective of this study is to find the total resistance and the free surface flow caused by the moonpool when the drillship is at low forward speed condition. Drillship with and without moonpool are considered for the study. Proven packages are used to calculate the calm water resistance of the drillship with moonpool. The incremental change in resistance caused by the moonpool in forward motion is a measure of water motion inside the moonpool for that particular field.

Control devices are selected in the preliminary design stage of any large platforms. This is true for deciding fin area for roll/pitch control of moving platform and thruster sizes and numbers for maneuvering assistance in the case of very low speed conditions. For moored platform the excursions are to be determined to activate the thruster system to reduce the line tension. In the case of a drill ship with moonpool there are some additional parameters of interaction. To some extent the parameters can be contained by optimizing the size and shapes of moon pools on board ships. The dynamics of a moored platform fitted with moon pool are determined here. Such responses are necessary to arrive at the actual sizes and numbers of thrusters to keep the vessel within the tolerances of excursion for ease and accurate operations. © IFAC.