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Large water motions can occur in the moonpools of vessels operating or transiting in waves. In the last decade, the size of moonpools has significantly increased. Larger moonpools allow to conduct activities in parallel and thus to cut the operation costs. However, the water motions in the moonpool also tend to become more violent when the moonpool size increases. This can result in unsafe working conditions due to water on deck, and reduce workability if the motion behaviour of the vessel is affected. This can also lead to structural damages due to slamming on the equipment installed in the moonpool.

To reduce the water motions, moonpool damping devices are commonly used. However, this is not always the ideal solution as these devices are expensive to produce and maintain. They also actually reduce the moonpool working area. These observations show that a practical methodology involving reliable tools is required to help the industry to optimise moonpool designs.

Guidelines should assist the designer in understanding the effect of the moonpool on the vessel’s hydrodynamics. They should also show how to predict the water motions inside the moonpool and to assess the structural design loads. An improved moonpool design will lead to an increased workability, a lower risk of damage and a safer work environment. These all contribute to lower costs.