The influence of wind, waves and current on the dynamic behavior of a single-point moored ship is investigated. Numerical simulations were used to compute the low-frequency motions of a tanker in the horizontal plane and the bow hawser force. Parameters varied comprised loading condition, hawser length and environment. A detailed overview is given of the theory for calculating the various force contributions in the numerical model. The onset of unstable motion behavior is described for both steady and unsteady wind, wave and current conditions. Unstable behavior tends to be more predominant for the lightly loaded condition. In the fully loaded condition the vessel behavior is generally very stable, except when the current direction is unsteady.