Performance of a windsurfing sail under steady condition.

This research investigates the aerodynamic forces and moments acting on a windsurfing sail during steady sailing. We performed wind tunnel experiments on a scaled-down sail model to measure the aerodynamic forces and moments at varying angles of attack and rig-back (swept-back). The study found that increasing the rig-back angle resulted in lower lift, drag, rolling moment coefficients and lift-to-drag ratio. Using kinematic considerations, the aerodynamic data was transformed into key performance parameters, including driving force, side force, and rolling moment. The study emphasis on the sail's aerodynamic rolling moment by taking into account a maximum righting moment threshold from the sailor. This threshold can restrict the maximum achievable driving force from the sail, and is particularly important at high apparent wind speeds. The study suggests that higher rig-back angles can be beneficial when the maximum driving force is restricted by the moment threshold. In these conditions, the reduction in sail rolling moment from a higher rig-back angle can offset the potential reduction in lift-to-drag ratio. This finding provides valuable insights into the optimal techniques for improving windsurfing performance under steady sailing conditions. This study contributes to the understanding of the underlying physical principles governing windsurfing and provides a basis for further research in this area. • Higher rig-back angles can be advantageous when sailing upwind and at higher relative travelling speeds. • Reduction in sail's rolling moment from a higher rig-back angle can offset the reduction in lift-to-drag ratio. • Sail's rolling moment is the most pertinent at low true wind angle, high relative travelling speed and high true wind speed. [ABSTRACT FROM AUTHOR]