Ship handling simulator should have capabilities of calculating ship motions (heave, pitch, and roll) at given sea state and displaying the calculated motions through a real-time 3D visualization system. Motion solver of a ship handling simulator generally calculates those motions in addition to position for an own ship, a main simulation target, but provides only position information for traffic ships. Therefore, it is required to simulate real-time traffic ship and buoy motions coupled with ocean waves in a ship handling simulator for the realistic visualization. In the paper, the authors propose a simple dynamics model by which ship and buoy motions are calculated with the input data of wave height and discuss a method for the implementation of a ship and buoy motions calculation module.