Pumping: A windsurfing technique through the lens of physics

In light wind conditions, windsurfers use a dynamic technique called “pumping,” which involves rocking the sail back and forth to generate speed. But what factors specifically influence the effectiveness of this maneuver? Researchers [1] at ESPCI Paris – PSL sought to answer this question through a groundbreaking experimental study.

To simulate real-world sailing conditions, the team used a small rigid sail oscillating around an average angle of attack in a controlled-flow hydrodynamic channel. By varying the frequency, amplitude, and average angle of the oscillations, they analyzed how these parameters affect the forces acting on the board.

The results show that the propulsive force, the force that propels the board forward, increases significantly with the intensity of the pumping, represented by the product of frequency and amplitude. Furthermore, unlike in a static situation, pumping delays the onset of a stall and increases lift. Interestingly, beyond a certain oscillation intensity, the sail even generates a net propulsive force, reducing crosswind drag.

These experimental data also provide a better understanding of how to manage course and propulsion during a race. When sailing upwind, optimizing the average angle of attack and the intensity of pumping can significantly improve performance, reducing lateral drift and increasing speed.

These findings open up new practical possibilities for athletes. By subtly adjusting their movements in line with these recommendations, they could not only make better use of light wind conditions but also refine their racing strategy, gaining speed and efficiency during competitions.