A multi-pump, multi-piston power take-off wave energy converter ((MPPTO)-P-2 WEC) has been proposed for use with a novel renewable energy harvester termed the Ocean Grazer. The (MPPTO)-P-2 WEC utilizes wave motion to pump via buoys connected to pistons working fluid within a closed circuit and store it as potential energy that can be converted to electricity via turbines. This paper introduces the mechanical design and model-based performance prediction of a single-piston pump that constitutes the basic building block for the (MPPTO)-P-2 WEC. Results provide preliminary validation of aqueous lubrication as a viable means of reducing friction and wear, suggesting that water-based hydraulic fluids can prohibit solid contact at the piston-cylinder interface while reducing volumetric leakage, and allowing for an estimation of the energy extraction efficiency for the mechanical pumping system. Pending more thorough and extended tribological investigations using the methodology introduced in this paper, findings suggest that the overall system efficiency will be dictated by the hydrodynamics of the buoys actuating the pumping system. (C) 2016 Elsevier Ltd. All rights reserved.