In this paper the comparison of aerodynamic sail force measurements from model scale wind tunnel and full-scale tests is presented. Wind tunnel testing of yacht sails is an effective design tool, but is at present mainly used for comparative testing. Comparing wind tunnel to full-scale data is important to better understand the associated scaling effects and make wind tunnel testing more accurate for quantitative sail force prediction. The full-scale data is taken from the sailing yacht DYNA developed at the Technical University of Berlin in Germany and is based on a 10-meter International Measurement System (IMS) cruiser/racer. For this project a 15% scale model was developed and upwind and downwind sail configurations comprising mainsail, genoa III and spinnaker were tested in the Twisted Flow Wind Tunnel (TFWT) of the University of Auckland. The parasitic drag was measured in the wind tunnel and compared to approximations used in velocity prediction programs (VPPs). The influence of the sails on the flow above the mast where the anemometer is located was investigated in the wind tunnel and the full-scale results are corrected to take this effect into account. The curves of lift and drag coefficient against the effective wind angle are compared to the coefficients obtained from the full-scale measurements. For the upwind configuration a significant force component up the mast was observed and its influence as the yacht heels was assessed. Comparing the results highlights the difficulties associated with modelling sail forces but also shows that wind tunnel and full-scale measurements relate to each other.
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