Extreme load analysis is an essential step in the design of structural and mooring systems for wave energy converters (WEC). The current study aims to evaluate the structural loads on the MARMOK Oscillating Water Column (OWC) WEC under both regular and irregular wave conditions, as well as to evaluate the effectiveness of its station keeping (mooring) systems. The project employs the open source computational fluid dynamics simulation software OpenFOAM to model the fully moored floating system. The WEC device hydrodynamics are validated against laboratory data for free decay in heave and pitch motions. In addition, the station keeping model is validated against mooring tension static offset tests and benchmarked against experimental data in irregular waves. An elegant method of numerically recreating irregular wave inflow conditions from empirical measurements is shown which allows for consistent comparison between the model and experimental results. The calibrated numerical model is then employed to study the full-scale system’s responses. Preliminary results of structural loadings on the fixed and floating spar buoy (with one mooring configuration as sample) are presented in the paper.