Fig. 8. Measurements of the roll torque and roll velocity at a tow speed of 1.34 m s^–1 for the case shown in Fig. 4 (blue) and a tow speed of 0.46 m s^–1 for the case shown in Fig. 6 (green). Observe the presence of hysteresis in the latter in comparison with the former. The hysteresis is attributable to the slower development of the Kutta condition at lower speed.