Direct Drive
During the mid-1980s, Professor Brad Blackford used direct drive on the first windmill boat that he built and entered into a trans-harbour sailboat race at Halifax, Canada. He sailed directly into a prevailing headwind to win the race. Axial-flow wind turbines would still generate power when set at 45-degrees from water surface, with flexibility to divert up to 20-degrees horizontally from headwind direction. An angled driveshaft on Blackford’s boat connected the windmill that was mounted high above the bow to a propeller submerged below the stern, perhaps setting a precedent for larger scale, future wind-powered catamaran vessels.
Number of Blades
The original into-the-wind boats built by both Jim Bates and Prof. Blackford were propelled into the headwind using 3-bladed axial- flow turbines. Peter Worsley has built wind-powered vessels that sail directly into the headwind using 6-bladed rotors. He set each blade at a maximum angle of 45-degrees to the driveshaft, resulting in a slower turning turbine that drives a propeller and has sailed a vessel directly into a headwind. Recent developments in dual-rotor axial-flow wind turbines include designs where upstream and downstream rotate in the same direction and also designs where upstream and downstream rotors spin in opposite directions.
Test results involving a pair of 5-bladed rotors counter-rotating on the same horizontal-axis suggest possible future application in vessel propulsion. Wind turbine powered vessels are subject to limitations on blade diameter along with its weight and height above the deck. In such operation, each of the rotors would be installed on a horizontal-axis upstream and downstream sides of a gearbox placed at the top of a tower, with concentric counter-rotating vertical driveshafts inside the tower. At the bottom end, bevel gears and a differential would recombine power from the vertical shafts to drive a propeller with steering capability.
Vertical-axis Turbines
A vertical-axis turbine offers the advantage of being able to directly drive a propeller, including an axial-flow propeller operating on a vertical axis and using inlet and outlet ducts to redirect water to achieve propulsion. A Voith- Schneider type cam-type mechanism located below the turbine assembly would continuously reset turbine blade angle during each assembly rotation cycle, to allow forward thrust below water to exceed wind
drag above water. Vertical turbine blades that resemble air foil sails would continually change angle and duplicate the sail angles of a sailboat tack-sailing into a headwind.
Installing a narrow-angle deflector upstream of counter-rotating vertical-axis twin turbines of small diameter that inter-mesh like gears, would redirect the headwind to the downstream side of each turbine and reduce drag by shielding the upstream side from air flow. The air deflector would allow the vessel to sail within 15 degrees of wind direction, assuring that both turbines provide propulsion. At larger angles from the headwind, a single turbine would remain operational and assisted by either deck-mounted sails or airborne kite-sails. Both a single turbine with movable blades and twin counter rotating turbine would require further research and testing.
114 | ISSUE 106 | DEC 2023 | THE REPORT
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