<p>A three-dimensional panel method is developed to investigate the seakeeping performance of two parallel ships advancing in head and oblique waves. In this method, the fluid domain is partitioned into two regions by introducing a virtual control surface. In the inner part, the Taylor expansion boundary element method is used, whose kernel function is the Rankine source; in the outer part, the free surface Green function with the forward speed effect considered is adopted. The velocity potentials and normal velocities on the virtual control surface are equal for the inner and outer domains. Moreover, the numerical estimation method for viscous roll damping recommended by the ITTC is included in the present method. This hybrid method is validated through the previously measured motions of two ship models, and the present numerical results are in good agreement with those of the experiments. Furthermore, the influences of longitudinal distances and wave heading angles on six-degree-of-freedom motions and the hydrodynamic interaction between the present two ship models are discussed in detail.</p>