On the avoidance of parametric roll in head seas

Parametric rolling in head seas can cause serious safety issues for ships with the possibility of cargo shift, damage and difficult working conditions for crew. This work investigates the prediction of its occurrence and the factors that influence its onset and magnitude. It also seeks to establish the effect of bilge keels on containerships. The threshold boundaries for the inception of parametric roll, for a typical containership operating in Australian ports, are established using the Mathieu equation. Good agreement was found between the numerical predictions and results from a set of towing tank experiments. Fitting of bilge keels to the containership model was found to be an effective way of reducing the roll angles induced by parametric roll, and in some cases their presence can prevent its onset. A simplified method for use by masters to avoid the onset of parametric roll is also presented.