The work performed in this thesis concerns the implementation of a water sloshing tank system (U-Tank) in the Inertial Sea Wave Energy Converter (ISWEC) in order to maximize the energy harvested from ocean waves. The conventional use of the water sloshing tank is like damping and stabilizing system, it creates a stabilizing force directly opposing the forces created by the passing wave in order to reduce the roll motion of ships. The purpose for which U-tank system was conceived is overturned and its simple working principle is exploited to broaden the performance bandwidth of the ISWEC device (designed for low-medium energetic sea-states) to oceanic applications.