The feasiblity of solar-powered, self-propelled data buoys
Creators: name: Egles, David William
Publisher: name: University of British Columbia
Year: 2010

description: The purpose of this study is to explore the feasibility of a recent development in oceanographic instrumentation known as an active drifter buoy. The active drifter is a self-propelled, solar-powered data buoy which has the capability of influencing its drift rate and direction with the use of a thruster/rudder system. This study examines the active drifters developed thus far, and discusses a series of experiments which provide sufficient information to predict the performance of a buoy offshore. The active drifter was conceived at the Institute of Ocean Sciences at Patricia Bay, B.C. Under the direction of Engineer G.R. Smith, a prototype was built and received limited testing in inshore waters. Seaboy Marine Services Ltd., a manufacturer of data buoys, began its own active drifter program in 1984, and in 1985 made its prototype available to the author for a series of experiments to define its capabilities and provide data for future development. The Seaboy active drifter was named Ranger 1, and had a shallow, spoon-shaped hull with a circular deck to maximize the area available for a photovoltaic array. The buoy was 2m in diameter and had a foil shaped keel 1m deep. A 12 V DC thruster combined with a 36 cm. model airplane propeller propelled the buoy at a speed of 0.50 m/s in calm water. The 210 peak watt solar array charged a bank of six 55 amp hour gelled electrolyte lead acid batteries and provided the power to operate the electronics payload and for propulsion. The Ranger testing program included a measurement of the effective power of the hull at the B.C. Research tow tank facilities. Experiments in the tow tank revealed that a design speed of 0.50 m/s required 4 watts of thrust, and that a static aft trim was required to prevent the buoy from submerging into its own wake. Extensive inshore tests were performed on the Ranger buoy in Elk Lake, near Victoria. These tests showed that the actual power required to propel the buoy at 0.50 m/s was 32 watts. Downwind drift tests showed the buoy travelled at a rate of 5% of the lm wind speed. Upwind, the combined effects of surface drift, waves and wind drag reduced the forward buoy speed by a factor equal to 5.4% of the wind speed, and the maximum speed in which the buoy could make forward headway was 10 m/s. A simulation based on the results of these experiments was performed to predict the performance of an active drifter deployed at Ocean Station Papa (50°N, 145°W). At this site, the average wind speeds are 10.5 m/s, with surface drift currents equal to 3.3% of the wind speed. With an average daily total insolation of 9.6 MJ/m² the buoy would be able to motor 12.7 hours a day. In these conditions, the active drifter could reduce the annual drift rate to 43% of a comparable unpropelled buoy. This is comparable to a deep-drogued spar buoy, indicating no significant improvement inperformance over the less sophisticated buoys commonly in use. The simulation shows that for an active drifter buoy to become a practical alternative to buoys now available, changes must be made in the hull shape to reduce drag and the effects of winds and waves on buoy mobility.