Laser (ILCA) S-turn technique when sailing downwind

This simulation was inspired by Riley Schutt's doctoral dissertation "UNSTEADY AERODYNAMICS OF SAILING MANEUVERS AND KINETIC TECHNIQUES" at Cornell University. Shutt and his team equipped a Laser with an array of camera's & sensors to record all the motions and sail shape changes of the boat while sailing. In addition to the S-turn downwind sailing technique, he looked at leech flicking upwind and roll tacking.

In our first simulation, we look at the S-turns. Quite complex, with simultaneous heading changes (S-turns), rolling of the boat (heel), sheeting & twisting of the sail and the sailor's motions. We also added a Windex to the mast top to record the apparent wind changes (inset). The variation of the apparent wind angle during one S-turn cycle is up to 90 degrees.

The rock&roll increases the driving force of the sail quite dramatically, up to 75%. The increase appears to be sensitive to the timing of the mainsheet adjustments, and of course, the amount of roll.

(c) WB-Sails 2022