Nonlinear hull girder loads of a RoPax ship

•Numerical and experimental studies of nonlinear wave loads are presented for a RoPax ship.•Numerical method is based on the transient Green function.•The time derivative of the velocity potential is solved using an acceleration potential method.•The calculation method can predict the nonlinear loads for the model test ship.

Numerical and experimental studies of nonlinear wave loads are presented. A nonlinear time domain method has been developed and the theoretical background of the method are provided. The method is based on the source formulation expressed by means of the transient three-dimensional Green function. The time derivative of the velocity potential in Bernoulli's equation is solved with a similar source formulation to that of the perturbation velocity potential. The Wigley hull form is used to validate the calculation method in regular head waves. Model tests of a roll-on roll-off passenger ship with a flat bottom stern have been carried out. Model test results of ship motions, vertical shear forces and bending moments in regular and irregular head waves and calm water are given. The nonlinearities in ship motions and hull girder loads are investigated using the calculation method and the model test results. The nonlinearities in the hull girder loads have been found to be significant and the calculation method can predict the nonlinear loads for the model test ship.