A wave energy dissipator (WED) is proposed in this paper, composed of two asymmetric hinged floaters and two hydraulic cylinders, with the purpose to resist wave-induced relative rotation around the hinge. Experimental studies are performed to explore its performance under a wide range of regular waves. Based on Reynolds-averaged Navier-Stokes equations, a 3D numerical model is set up, considering the non-linear interaction of wave and WED. The agreement between the experimental and numerical results is good. With the validated numerical model, the influence of the WED geometrical factors on energy conversion and wave transmission is examined. For a given raft length, the difference in energy conversion between the two multiplicative inverse fore-and-aft raft lengths is significant, which is dependent on the wave frequency. However, as for the wave transmission, the difference in between is insignificantly small, almost independent of the wave frequency. The findings demonstrate that, for energy conversion, its maximum value per unit length corresponds to a large fore-and-aft length ratio but a small total raft length. The combination of experiments and simulations provides reference for both understanding of hydrodynamic behaviours and design including parameter selection of the dissipator.