The aerodynamics of symmetric spinnakers

Twelve parametric spinnaker models were built and tested in a wind tunnel. In these models, five sail shape parameters were varied - cross-section camber ratio, sail aspect ratio, sweep, vertical distribution of camber, and vertical distribution of sail width. Lift and drag forces were measured for a range of angles of attack, and the results were analyzed for three points of sail. It was found that low sweep (more vertical) spinnakers are faster than spinnakers with high sweep, and that the optimum camber ratio depends on both the point of sail and aspect ratio of the sail. On a run (sailing directly downwind), the only significant geometric parameter is projected sail area. The implications of these results to sail trim are discussed. A description of the sail shapes and corresponding force coefficients is presented for future validation of Reynolds Averaged Navier-Stokes simulations of spinnaker flow fields.