Pressure distributions on modern asymmetric spinnakers

An electronically scanned multi-channel pressure system was used at the Yacht Research Unit's Twisted Flow Wind Tunnel (University of Auckland) to test 3 asymmetric spinnakers. The sails were designed for the most recent America's Cup Rule (AC33) and tested on a large-scale model. The present paper focuses on pressure measurements on three asymmetric spinnakers, which were measured on 5 chord-wise sections with 11 pressure taps on each section. All the 3 sails were tested at apparent wind angles of 40°, 55° and 70° and at heel angles of 0°, 10° and 20°. The 3 sails were firstly tested in uniform flow and then one of the sails was re-tested in twisted flow conditions. It was found that the suction peak on the A2 sail increased when the model was heeled to 10°, and then decreased when the heel angle was increased further to 20°, which agrees with the similar observed behaviour in the drive force variation with heel angle. Measurements in straight and twisted flow showed that all sail's sections gave higher suctions in the twisted flow and a corresponding increase in the drive force.