The effect of slamming and whipping on the fatigue life of a high-speed catamaran

In order to optimise the structural design of lightweight high-speed vessels knowledge is required of the effect of sea loads on their structures, with respect to both ultimate strength and fatigue life. This paper reports on an investigation into the influence of slamming and whipping on the fatigue life of a large high-speed catamaran. Full-scale measurements of slam events were conducted on a 98m Incat catamaran to investigate its slamming behaviour in a variety of sea conditions. The full scale results were then used to determine the influence of the presence of slam events on fatigue life. In addition the effects of significant wave height, slam occurrence rates, slam peak stresses, whipping behaviour on fatigue life were examined. The fatigue life was found to reduce significantly with the presence of slam events. Therefore a reduction in slamming may prolong the fatigue life of a vessel markedly. The fatigue life was found to reduce significantly as wave height increases, as slam rate increases and slam peak stress increases. However small slam events were found to have little or no influence on fatigue life. Whipping behaviour, in particular decay coefficient, may also strongly influence fatigue life.