This paper considers the effects of mast rotation on the performance of sails, using RANS based Computational Fluid Dynamics. The paper focuses upon the effects of masts and their influence on the leading edge separation of sails. Pressure distributions are compared for various mast shapes, representing 4 generic profiles. The lift and drag forces are computed and compared at different angles of mast rotation. The results obtained show that the rotation of mast sections to windward gives a clear improvement in their performance, offering large reductions in drag and increases in lift.