Parametric rolling in head seas - an Australian perspective

The onset of parametric rolling in head seas has been known to cause serious safety issues for ships, particularly containerships. The aim of this work was to investigate the prediction of the occurrence of parametric roll and the factors which influence it. The threshold boundaries, for the inception of parametric roll for a typical containership were established using the Mathieu equation. A series of model experiments was then conducted to validate the theoretical predictions for the inception of parametric roll and investigate the influence of wave height, wave length and GM on the inception of parametric roll. For all the GM values tested reasonable agreement was found between the numerical predictions and the experimental results. A reduction in wave height was found to reduce the range of encounter frequencies for which parametric roll will occur. Parametric roll was found to occur for a range of wavelengths provided that the encounter wave period was in the critical range.