Hydrodynamic numerical models of Wave Energy Converters (WEC) contain hydrodynamic coefficients that are commonly obtained from numerical codes that solve linear potential flow problems using Boundary Element Methods (BEM codes). The assumptions made by the BEM codes in their calculation of the linear hydrodynamic coefficients are violated by the large and nonlinear motions that wave activation body class WECs often go through during operation. In this study, Forced Oscillation Tests were used to evaluate the hydrodynamic torque coefficients estimated for an Oscillating Wave Surge Converter (OWSC) WEC by two BEM codes; WAMIT and Nemoh. The paper describes the tests and the active Force Feedback Dynamometer test rig used to perform them. The results indicate good agreement between the BEM codes and experimental data for small angular displacement amplitude oscillations, as expected; up to 0.3 rad. The torque not predicted by the BEM codes is presented and shown to have an amplitude and phase that vary throughout the range of tests performed.