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20 H umans have been harnessing natural forces for our own purposes for thousands of years, and there are few things as satisfying as making use of what is essentially free energy for propulsion, something that sailing-boat builders have turned into a fine art and a precise science. Wave energy, however, has not been exploited to anything like the same extent for propulsion, or anything else for that matter. That suggests we have been missing a trick for a long time because at sea, waves are almost always present – flat calms are rare and usually short- lived – and wave propulsion systems can be designed to take advantage of waves from any direction to propel a boat in any direction, slowly but with almost no limits on range or endurance. That is what UK company AutoNaut has achieved with its family of foil- driven USVs that range in length from 2 to 7 m, with solar panels to charge its batteries and power its navigation, communications and payload systems, the steering and an auxiliary electric thruster for when wave power is not enough. The foils convert the vertical motion caused by waves lifting a boat up out of the water and dropping it down again into forward thrust. It’s a process of such simplicity that it raises the question of why it hasn’t already been widely exploited, despite a history of experimentation stretching back to 1895, when Hermann Linden of the Naples Zoological Station built his original Autonaut. This 23 ft boat with flexible flaps mounted at the bow and stern was able to reach a speed of about 4 mph (3.5 knots) while towing two boats carrying two people each. When Mike Poole, executive director of AutoNaut, revisited the technology and began his own experiments in the Rock and roll February/March 2017 | Unmanned Systems Technology The hull is designed to exploit waves that impinge on it from the side as well as on the bow and stern to provide propulsion power (Courtesy of AutoNaut) Wave propulsion’s time looks finally to have come with this simple, reliable and long- endurance USV. Peter Donaldson reports