Abstract
In the movement of a sailing boat, the forward driving force named thrust and the force tending to drive the boat sideways vary according to the various alterable factors e.g., the speed of the wind, the direction in which it acts, the speed of the boat, etc. In this papar, the writer, with the figures which Eiffel has given for a thin rectangular aerofoil of 6: 1 aspect ratio and various arch, calculated the coefficients of thrust and side force against the direction of real wind from bow and the ratio of the speed of the boat to the speed of the wind. Then, making use of those calculated results, some considerations about the following subjects are presented by the writer with some assumptions. (a) The angle of attack in which the thrust is greatest. (b) The lee way of the sailing boat. (c) The course of the boat in the case when the required time for sailing to get to a weather side destination is minimum.
