The behaviour of a bow hawser moored tanker exposed to wind, waves and current has been studied by means of computer simulations. An overview is given of the theory used in the simulations. Some comparisons are shown with experiments. Tanker motions and bow hawser forces were investigated both in a stationary and in a dynamic, time-varying environment. In the stationary environment steady wind and current are considered and in the dynamic environment the effects of waves and unsteady wind were studied. In particular, the occurrence of unstable behaviour is investigated. Lastly, it is shown that time-dependent current can influence bow hawser forces significantly.