Examination of the stability of trawlers in beam seas by using safe basins

The focus of this study is to examine the transverse stability of BSRA trawlers in beam seas using both numerical and analytical safe basin concepts and also shows how the concept of safe basin can be utilized for the assessment of the stability of trawlers. In the first part of this study, the nonlinear ship roll motion equation and the main parameters that induce ship capsizing in beam seas are analyzed using the concept of numeric safe basin. Then, the safe operating conditions of trawlers such as maximum allowable wave height and wind velocity are obtained for given loading conditions. In the second part of this study, analytic safe basins of nonlinear rolling motion are determined for given operating and loading conditions using the Lyapunov direct method. It is observed from the comparisons of analytically and numerically obtained safe basins that the analytically obtained safe basins are coherent with numerically obtained safe basins but beside this coherency analytically obtained safe basins are more conservative.