Wave-induced ship motions, loads and hydrodynamic pressures are evaluated by a Rankine source method for two different types of practical merchant ships : a VLCC and a large-container ship. The numerical results are compared with the experimental results obtained by the authors. They are also compared with the results calculated by means of a modified strip method in order to investigate the three-dimensional effects on ship motions, bending moments and hydrodynamic pressures. The relationships between hull characteristics of the ships and their hydrodynamic responses are discussed in detail. It is concluded that the Rankine source method could be an effective numerical tool for the evaluation of wave-induced loads acting on practical merchant ships and thus may be used in the structural design of practical ships.