A monoplane Wells turbine was tested during the experiments conducted at sea on a small scale model of a REWEC (Resonant Wave Energy Converter) breakwater. Tests aimed at analyzing the behaviour of the turbine subjected to randomly varying oscillating air flow, variable according to the intensity and spectral characteristics of the sea. During the experimental campaign, 261 records (sea states) were acquired in order to characterize the behaviour of both the plant and turbine. Thanks to the measurement techniques ad hoc developed for tests at sea and described in a companion paper, it was possible to determine the values of torque coefficient T* and pressure coefficient ∆p* as a function of the flow coefficient, φ. Because during each sea state lasting five minutes, data on dozens of cycles of oscillation were recorded, it was possible to perform a statistical analysis of all the available data, with regard to the sign of φ and of its derivative. The results were classified by maximum oscillation amplitude and peak frequency of the spectrum. The paper presents the results of the statistical analysis carried out by highlighting effects on the stall condition at high values of flow coefficient and on the hysteresis between the phases in which the flow rate is growing and those where the flow rate is decreasing. Finally, the influence of the spectral components at higher frequencies on the hysteresis phenomenon was highlighted.