This paper presents the assessment of the optimum performance of a wave energy converter. In this device which is hinged at the seabed, wave forces act on the face of a collector body, carried on an arm that rotates about a fixed horizontal axis. The collector body oscillates at about the frequency of the ocean swell generating high power from this relatively small and economical device. The performance of the device is investigated using numerical hydrodynamic analysis and the wave tank experiment for a model at a nominal scale of 1/100. Also the optimum mean power output of the device in irregular wave climates is assessed. A first-order method is used to calculate the mean power spectrum of the device in waves of dissimilar spectra. It is shown that the choice of tuning period has a major effect on the power absorbed, hence on the power output.