Ocean Wave Harvesting for Supplemental Powering of a Small Autonomous Boat

This study presents the concept of a small autonomous catamaran for operation in remote offshore areas for long duration. The relative linear motion between the hulls and the main deck is converted into a rotational motion of an electrical generator to harvest wave energy for supplemental powering and improving the overall energy efficiency of the craft. The design of “DavLab” catamaran is optimized by matching the natural undamped frequency of the system to the frequency of dominant waves for a top referenced heaving absorber. In addition, numerical simulation results showed that increasing the design waterline reduces vertical motion, and the hull responses increase with increasing length to beam ratio and decreasing beam to draft ratio. Consequently, the combined motion at the power take-off system positions were increased by selecting a slender body with L/B = 5.88 and large draft B/T = 1.89 for large motion at operating conditions. In head seas, the required power for a 1/3 scale model at Froude number equal to 0.6 is predicted about 3.5 W. For supplemental powering with wave energy harvesting, the wave run predictions in head seas for a dominant period of 2 seconds and significant wave height of 0.2 m were evaluated at two model speeds, namely Vm0 = 0 m/s and Vm1 = 2.66 m/s corresponding to Froude number 0 and 0.6. Predictions for maximum generated power are 4.7 W and 12.7 W at Vm0 and Vm1 respectively. Therefore, the 1/3 scale model of the Catamaran suspension is to be built and tested in Davidson Laboratory Towing Tank #3 in regular and irregular head seas.