The substantial water motions that can occur inside a moonpoolwhen a ship is operating in a formed sea represent a criticalissue for operators, as they imply an interruption of subsea activities (e.g. delay in ROV deployment) or even a threat to thesurvival of the equipment placed inside or around the moonpool(e.g. riser connected to a BOP). In a perspective of reducingdowntime caused by moonpool inactivity, substantial effort hasbeen made over the past year to better understand the circumstances of such water dynamics and devise mitigation measures. Works of among others Fukuda  or Molin  show that the moonpool motions can be described as either piston mode, in other words a vertical displacement of the watercolumn, or as horizontal sloshing modes, which natural frequencies can be approximated by closed-form expressions involving moonpool geometry and draught. The effect of damping devices, such as side wall flanges, has been widely investigated, notable publications include those of Fukuda  and Aalbers .State-of-the-art prediction of moonpool flows has undergonesome significant changes over the last years.