Experiments have been undertaken to assess the performance of the six-float version of the moored multi-mode multi-float wave energy converter M4. Time-domain linear diffraction modelling slightly underestimates power capture except for larger wave periods. Without power take off the relative response and platform acceleration were quite linear with wave height up to extreme conditions. Converting to a hybrid wind-wave platform supporting a wind turbine on the central mid float with damping plates on the bow and mid floats reduced wave power capture to about 40%. The linear modelling approximately predicted motion and power with an overall drag coefficient of 6 for the plates and surprisingly with their added mass reduced to zero; this is thought to be due to the lift force from bound circulation for bodies in orbital flow opposing the inertia force. Accelerations at hub and hinge without PTO were approximately linear. This study concerns hydrodynamics only.