To maximise the energy output of wave energy converters (WECs), large structural motions are desired. When simulating WEC performance in Computational Fluid Dynamics (CFD) based numerical wave tanks, these motions must be explicitly accommodated in the computational domain. Using well established mesh morphing (MM) methods, this explicit accommodation results in deformation of control volumes (CVs)/mesh. Thus, large amplitude WEC oscillations may lead to highly distorted CVs and push MM models beyond the limits of numerical stability. While advanced numerical mesh motion methods, such as overset grids, have been developed in commercial CFD codes to overcome these issues, little use of these methods can be found in WEC analysis. However, recently the overset grid method (OSG) has been made available to a wider user community through its release in the open source CFD environment OpenFOAM [1, 2]. To evaluate the performance of the OSG, this paper will compare the classical MM method and the OSG against experimental tank test data of the WaveStar device [3].