Nonlinear effects are demonstrated to be relevant for different aspects on the development of wave energy converters with a particular importance on the assessment of the behaviour and power production capabilities, and design of mooring lines and energy maximising controllers. However, mathematical models that incorporate relevant nonlinear effects beyond the viscous effects are scarce and computationally heavy. Therefore, the present paper compares two open-source numerical platforms that incorporate nonlinear Froude-Krylov (NLFK) effects: the WEC-Sim code developed by NREL and the NLFK4ALL code. The comparison presented here is carried out for the Sparbuoy floating oscillating water column device. Results show a good agreement in heave, both for the floater and the water column, while some discrepancies are found in surge and pitch with longer waves. These discrepancies are found to arise due to differences in the computation of the forces for NLFK and, particularly, the mooring system.