Physical experimental and 3D numerical free decay tests are performed for a stationary oscillating water column (OWC) device with various underwater opening heights and power take-off (PTO) mechanisms. Numerical model results are verified with experimental data. Equivalent linear damping of the system is found by using logarithmic decrement method. Natural and resonant frequencies and added mass are calculated. For the OWC with the orifice, it is found that damping ratio decreases quadratically with increasing orifice ratio and linearly with increasing relative opening. Resonant frequency is found to be a linear function of both opening size and PTO damping. Calculated natural frequency values are compared with extensively used formulas, which are found to overestimate the OWC natural frequency. For the first time, an empirical formula for the natural frequency of a fixed OWC is proposed. Added mass is found to be independent of orifice size and underwater opening height. For the OWC with the porous layer, no noteworthy change is observed for the natural frequency and added mass compared to those of OWC with orifice. However, damping of the system is quite altered, while its change due to the variations in the permeability and under water opening height has similar characteristics.