In the previous paper, one of the authors and Prof. Fujino, based on a nonlinear strip synthesis, proposed a method to calculate the vertical motions and vertical wave loads of a high-speed craft in head sea. The validity of this method are verified practically through the comparison with model tests data. Furthermore, in this paper, following the similar synthesis scheme, a practical method for predicting the motions of a high-speed craft in oblique waves is presented and applied to an existing craft to clarify its fundamental characteristics of vertical and transverse motions in bow (or beam) sea. In the method presented, the time-varying submerged hull surface and the coupling effect between transverse and vertical motions are considered. Moreover, using the momentum theory, the nonlinear flare impact and dynamic lift are also taken into account. Besides, the equations of motions are described by the body-fixed coordinte, rather than the vehicle-carried vertical frame which is used conventionally. To prevent the numerical divergence due to the drift of sway and/or yaw motions in the time domain simulation, artificial springs in sway and yaw modes are introduced. The effects of the spring constants on the predicted ship motions are also discussed.