Mitigation of slamming of large wave-piercing catamarans

The Wave Piercing Catamaran (WPC) design of INCAT Tasmania reduces motion responses in moderate seas and provides a high level of protection against deck diving in large seas. However, in large seas slamming will occur as the arch between outboard and central bow hulls fills, imposing large transient loads which can exceed the vessel weight. Consideration is given here to reducing slam loadings by variation of key geometric parameters of the WPC bow design and by operation of ride control system (RCS). Due to the complexity of wave slam loads, model testing provides an essential basis for design development and validation of numerical solutions. A segmented hydro-elastic model of the 112m INCAT WPC has been developed with adjustable height of the wet deck and length of the centre bow. Dynamic wave slam forces and whipping responses are modeled on the basis of the whipping mode frequency and damping. It is found that increases of wet deck height reduce impulsive slam loadings but lead to increased motions. Shorter centre bows reduce slam loadings and also reduce the vessel pitch motions. When the ride control system (RCS) is operated as a pitch damper the relative motion between the centre bow and water surface can be reduced by as much as 58% at the frequency of maximum relative motion. This reduction will confer significant benefits in terms of slam amelioration. The maximum relative bow motion occurs at a dimensionless encounter frequency corresponding closely to that at which most severe slamming is observed in the model test program.