This paper concerns the difficulties arising in the prediction of the impact loads associated with an extreme wave event. A new set of experimental observations are presented. These concern the impact loads arising on a slender horizontal cylinder located at varying elevations above the still water level. The experimental observations incorporate a wide range of wave forms. In each case, data is provided describing (i) the incident water surface profiles, (ii) the incident fluid velocities and (iii) the load components acting on the cylinder.

Comparisons between the measured data and the classical impact load solutions confirm a number of important departures. In particular, it is shown that as the wave becomes very steep (approaching the breaking limit) the vector sum of the horizontal and vertical velocity components at the water surface may deviate significantly from the normal to the local water surface. In such cases it becomes unclear exactly what direction the impact force acts. The present data suggests that this is, in part, dependent on the rate of inundation of the body. Furthermore, the present results also show that if the direction of the force is correct modelled, the variations in the predicted loading (or slamming) coefficient are much reduced.

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