We present recent results concerning the numerical simulation of flow around ship sails. The main purpose of our work has been to derive a numerical model which includes real effects to the utmost. The basic numerical model is made of a lifting surface code for the sail and a vortex method for its wake. This description of the flow is supplemented by considering the fluid structure interaction problem, the sea surface influence on the flow, the effect of non-homogeneous incoming flow (vertical wind gradient and gusts), the ship hull motion, and sail interactions.