In the following article an attempt has been made to present the characteristics of a sail by considering it as an aerofoil, the “ lift ” and “ drag ” being replaced by two forces mutually at right-angles in a horizontal plane, one force corresponding to the drag, acting in the same direction as the relative wind. It appears that skill in the art of sailing could be reduced, apart from other considerations, to ability to set the sail in the required position determined by its aerodynamic characteristics.