The high availability of energy within ocean waves is seen as an important and abundant alternative as a renewable energy source. This paper presents a numerical study of the submerged horizontal plate type wave energy converter, assessing its theoretical efficiency for several relative plate heights. The propagation and incidence of distinct wave periods through the device structure were simulated, and the device efficiency was evaluated disregarding the presence of the turbine under the plate. A total of six wave periods between 1.25 and 3.50 s with wave height of 0.06 m were considered for six different plate heights. The results allow to make theoretical recommendations on the converter performance. The multiphase Volume of Fluid model was used through a two-dimensional approach for air-water interaction and the conservation equations of mass, momentum and volume fraction transport were solved by the Finite Volume Method. The results of analysis allowed to observe that the highest relative plate height leads to enhanced submerged horizontal plate efficiencies among the simulated wave periods, as well as to identification of a theoretical device efficiency up to three times higher for larger wave periods than for shorter wave periods.