Aerodynamic performance of an OPTIMIST full-scale sail for various sail trims: An experimental study

Based on wind tunnel tests, the aerodynamic behaviour of a full-scale sail (2.7 m × 2 m) of the OPTIMIST boat is presented for various sail trims. The sail with its vertical mast was attached to a six component balance in a 3.5 m × 4.5 m cross-section of a closed circuit wind tunnel at the National Technical University of Athens. The aerodynamic force and moment vectors applied on the sail were measured for various angles of attack in the interval 10°–40°, for a free stream of 5 m/s and for four shapes of the sail, varying the tension applied on it. Its three dimensional shape was reconstructed using a commercial motion capture system, including three infra-red cameras and a number of spherical reflectors attached to the sail surface. Lift, drag, moment coefficients and the centre of pressure are presented as a function of the angle of attack and the sail trim, as well as the characteristic geometric features of the sail at various horizontal sections like the maximum camber and its location, its inlet-outlet and twist angles.