Roll Motion of a Ship in Random Beam Waves: Comparison Between Theory and Experiment

The results of an experimental study of a ship rolling in random beam waves at zero speed are presented. The experiments were conducted in a large wave tank using a 1:20 scale model of the fisheries protection vessel Sulisker. By digitally processing the roll response measurements, obtained over long periods of time, estimates of the probability distribution of the roll peak amplitudes were obtained and compared with some corresponding theoretical predictions. The theory was found to give good agreement with the experimental findings for four different wave elevation spectra. In particular, the experimentally observed deviation from the Rayleigh distribution at high peak amplitudes was correctly predicted by the theory. This deviation is largely due to the pronounced nonlinear character of the roll damping.