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Parametric roll

Parametric roll is an unpredictable phenomenon in which the ship starts to roll in head or stern seas. The roll angle can increase from a few degrees to over 30 degrees in only a few cycles. This footage was filmed in a demonstration held in the Ship Laboratory of Aalto University School of Science and Technology on November 18th, 2010. The model, a RoPax vessel, encounters waves head-on. In the first part nothing happens, but as the wave frequency is adjusted so that the encounter frequency is roughly twice the natural roll frequency, parametric roll occurs. As the wave height is increased, the rolling becomes more violent. It has been said that this is the phenomenon that caused the extreme rolling of the cruise ship Grand Voayger when it lost its propulsion in a storm.