Slamming kinematics, impulse and energy transfer for wave-piercing catamarans

Wave slam on high-speed wave-piercing catamarans involves interaction between unsteady hydrodynamics and structural response. For this class of vessel, the period of whipping and the duration of slam loading are similar, and hydroelastic simulation in model testing is important. The high Froude number results in relatively large heave and pitch motions that influence slamming. The model tests carried out were intended to identify the most severe slams possible. Slam loads increase with wave height and forward speed, and peak slam loading was related most clearly to the maximum relative velocity between bow and water surface. The peak load mostly occurred after the time at which the center bow arched cross section would fill with displaced water when calculated on the basis of the hull cross-section movement relative to the encountered wave and before the top of the arch reached the undisturbed surface of the encountered wave. For a 112-m vessel with 2500 tonnes displacement slams in 5.4 m height, regular waves would reach a maximum force of 2115 tonnes weight with a duration of 1.14 seconds and an impulse of 918 tonne seconds. The energy imparted to structural deformation would reach 3.9 MJ at full scale, of which approximately 1.0 MJ would be transferred into structural whipping. The results obtained in these model tests are broadly consistent with the most severe slam loads observed during sea trials.