For the economical operation of wave energy converts (WECs), energy maximising control systems (EMCSs) are included in the device design, introducing large structural motions. During the numerical modelling of WECs in CFD-based numerical wave tanks (NWTs), the structural motions must be explicitly accommodated in the finite volume domain. Using well known mesh morphing methods, large amplitude WEC oscillations may deteriorate the quality of the spatial discretisation, and push the NWT beyond the limits of numerical stability. To overcome this issue, advanced mesh motion methods, such as overset grids, have been developed; however, these methods are rarely used in numerical WEC experiments. To this end, the present paper aims to highlight the importance of advanced mesh motion methods, when modelling WECs under controlled conditions. To furthermore prove the feasibility of the overset method, implemented in the OpenFOAM framework, simulations of an uncontrolled WEC are performed, and results are compared to simulations using the mesh morphing method. It is shown that the overset method has potential to improve CFD-based models of controlled WECs, but, at the expense of increased computational cost.