This paper describes a numerical method to calculate viscous ship flow with the overset composite grid approach based on fortified solution algorithm concept. Communication among the grids is achieved by interpolation based on small volume elements. In the present computation, the composite grid consists of three component grids. The primary grid is constructed with respect to the ship hull, and the subsidiary grids are generated about propeller and rudder. Propeller effect is considered using equivalent body force distribution in propeller grid. The individual grids overset and, once combined, cover the entire computational domain. This feature allows computational grids to be generated quickly and easily. The hydrodynamic force characteristics on a tanker [ESSO OSAKA], moving with constant rudder angle, agree well with the model experiments. It is shown that the present method can be an effective CFD tool for complex body configurations.