To Twist, or Not to Twist? - A Scientific Attempt to Understand What We Think We Already Know About Sail Trim

摘要

The impact of mainsail sheet tension and traveler position on performance has been investigated, particularly under conditions when it is necessary to reduce power. Photographs of the mainsail on a Beneteau First 36.7 under various trim conditions were taken and analyzed to determine sail shape. The resulting shapes were used to create a CFD model, and the aerodynamics forces on the sail plan were determined. The results strongly suggest that for this boat it is more efficient to reduce power by keeping the main sheeted hard and lowering the traveler than by keeping the traveler up and easing the sheet, although a small amount of sheet easing is beneficial. The lift distributions for all sail trim combinations investigated are underloaded near the masthead relative to an elliptic distribution, which means that any additional twist in the main increases the induced drag. The difference in performance is almost entirely attributable to differences in the induced drag.