Parameters Affecting the Performance of the C-class Wingsail

Wing sails offer a different design challenge to those of more conventional soft sail rigs. This study was undertaken in order to assess which parameters influence wingsail performance of C-Class catamarans, and to what extent, the results from the wind tunnel can be applied in the design developments of future wingsails. A combined wing sail and Cclass catamaran was tested in the low-speed section of the 7’ x 5’ wind tunnel at the University of Southampton. Testing assessed the appropriate settings for the movable element of the multiple-element wing sail as well as heeling angle, trampoline porosity, spanwise camber distribution and gap at the foot of the wingsail. Both upwind and downwind conditions were considered through measurement of driving force, heeling force, lift and drag coefficients. The results demonstrate that low heel angles improve overall performance and that the gap underneath the wingsail foot adversely affects the generation of lift by the sail. An airfoil shaped trampoline is suggested in order to benefit both a reduced gap and a better control over the heel. For heavy wind condition, negative twist at the tip of the wingsail allows higher boat speeds.