An accurate prediction of aerodynamic and hydrodynamic loads on an offshore floating wind turbine plays a critical role in determining its operational stability, fatigue life and survivability, as well as optimising its power control system. Therefore, it is essential to develop an integrated aerodynamics and hydrodynamics model, which is capable of capturing both loading on and dynamic response of an entire offshore wind turbine system with high accuracy and reliability. Prior to developing such an integrated model, aerodynamics and hydrodynamics models need to be systematically examined, individually. In this study, the performance of the overset mesh solver in OpenFOAM for modelling aerodynamics of a floating offshore wind turbine rotor is evaluated. A benchmark test on the rotor of the National Renewable Energy Laboratory (NREL) 5MW turbine, which is designed to be mounted on a semi-submersible platform is performed. The predicted power and thrust for cases of the rotor with its centre fixed and undergoing pitching motion are compared between the overset mesh solver, a frequency-domain Naiver-Stokes Computational Fluid Dynamics code and the open-source Blade Element Momentum theory code.