Slam events of high-speed catamarans in irregular waves

Slam events experienced by high-speed catamarans in irregular waves were characterised through experiments using a hydroelastic segmented model. The model was designed to represent the dynamic behaviour of the full-scale Incat 112m vessel and to allow the measurement of the slam load on the centrebow and wet deck. It was tested in irregular head seas at two speeds relating to Froude numbers of 0.32 and 0.60. Nearly 300 slams were identified in the test data and analysed with respect to kinematic parameters. Slams were found to have a large range of magnitudes, with the largest equivalent to 1785 tonnes full scale (approximately 70% of vessel displacement); however, the majority of events were of relatively low severity. Difference in slam characteristics were found for the two model speeds tested; slams at the slower speed generally occurred further forward on the hull, prior to the wavecrest and with a bow down pitch angle. Immersion of the centrebow to the two-dimensional filling height of the cross-section between the centrebow and demihulls is shown to be a better indicator of slam occurrance than immersion to the top of the archway.