Unsteady Aerodynamics of Roll-Tacking and Roll-Gybing in an Olympic Class Sailboat

In this research, we study unsteady sail motion techniques used by Olympic sailors to increase sailboat propulsion. One such technique is for sailors to use bodyweight movements to roll the boat about its longitudinal axis. This motion is used especially for turning the boat in light winds, by either ``roll-tacking'' (upwind sailing) or ``roll-gybing'' (downwind sailing). When roll-tacking and roll-gybing, sailors dynamically roll the boat to increase their speed and propel their boats faster than using wind alone; this is in contrast to flat-tacking and flat-gybing, wherein the sailor keeps the boat level (and mast vertical) while turning. Each of these motions is characterized in on-the-water experiments using a Laser sailboat equipped with a GPS, IMU, wind sensor and GoPro camera array. Bringing these motions into the laboratory, we study the underlying vortex dynamics that are responsible for generating extra propulsion in roll-tacking and roll-gybing.