Theory and Experiments of a Free-Running Fishing Vessel in Stern Sea

Hydrodynamic aspects of a modern fishing vessel during manoeuvring in a seaway was studied theoretically and experimentally. The focus was on small frequencies of encounter, corresponding to following and stern quartering seas, where fishing vessels are susceptible to capsize. The numerical model was based on de Kat and Paulling [1]. The model combined a 6 degrees of freedom (DOF) blended seakeeping model with a 4 DOF non-linear manoeuvring model. The 3D non-linear Froude-Krylov and restoring loads were computed by pressure integration up to the incident free surface. The added mass, damping and wave diffraction loads were obtained by generalizing the STF (Salvesen et al. [2]) strip theory to partly include 3D flow effects by means of WAMIT. The simulated wave-induced surge forces over-estimated the experimentally measured forces by up to 50%. Excessive wave-induced surge forces led to predictions of broaching and surf riding, which did not occur in the experiments. Use of experimentally determined wave-induced surge forces gave good agreement between simulations and experiments