REEFS is a new multipurpose wave energy converter. It produces electric energy and contributes to shore protection. It is a large nearshore submerged device that can originate high waves breaking like the natural reefs do. The device makes use of the wave’s pressure and velocity spatial differentials, to produce electric energy. A laboratorial concept proof based in a small scale physical model (1.5:100) was already successfully performed. However, to further develop the device, it is necessary to analyze the impact of its geometry and deployment depth in power output. For such purposes, computational models have proved to be more affordable than experimental approaches. However, the novelty of the concept inhibits the use of already existing computational models. In this article, a mathematical model specially developed to assess REEFS power output is presented. It is a simplified model to enable expedient use required by the exploratory nature of the initial development stages. This mathematical model is solved numerically by a dedicated computational program. The results were compared with a laboratorial concept proof. After adequate calibration, the numerical model exhibited a good agreement with the laboratorial results, indicating it can be used for expedient assessment of the REEFS power output.