Opposite to other types of turbines for OWC wave energy converters, like the axial impulse or the Wells turbine, there is scarce information about radial impulse turbines. The interest in radial impulse turbine for wave energy is low because the available research on it shows lower efficiencies than the competitors. On the other hand, radial turbines present several advantageous features that make it a worthy option if the efficiency is improved. The purpose of the present work is to propose a new geometry, not focused on improving the rotor efficiency, but on reducing losses downstream of the rotor. This new design, taking previous geometries as a reference, was based on the classical 2-D angle computations optimizing the flow and blade angles for both inflow and outflow modes. After setting a balanced agreement between both modes, a numerical model with the new design was mounted on ANSYS Workbench which has allowed to speed up the whole process by using the specific tools set for turbomachines. Taking advantage of the simulation speed provided by the use of this model. A solidity optimization process was performed out on the new geometry to decide the required number of blades and vanes of the proposed turbine. Once, the turbine was well-defined, it has been compared concerning the previous turbine under both, steady and non-steady flow. The improvement has been remarkable, reaching a 10 % in steady efficiency and 6.7 % in non-steady efficiency with respect to the previous geometries.