Solar Xplorer is our solar powered autonomous boat. It is the only commercial offshore-capable solar powered autonomous vessel, and is the world’s fastest energy-harvesting autonomous boat. Consistent speed is one of the most important attributes for a reliable boat, since slower energy-harvesting vessels can easily be overpowered by strong currents and winds.
One of the greatest challenges in the design was coming up with a hull configuration that could support a large deck for an adequately-sized 1200 watt solar array, while still being seaworthy. A monohull simply doesn’t have the deck space and an overhanging deck creates other problems. A multihull (such as a catamaran or trimaran) is ideal in providing ample deck space, stability, and hydrodynamic shape, however, it is extremely challenging making a multihull self-righting, a necessary component of offshore voyaging.
After giving it much thought, our team came up with a patent-pending system of self-righting a trimaran through shape and positioning of the center of gravity and buoyancy.
The next step was developing a unique propulsion system. Our design is comprised of an inboard brushless electric motor. The large diameter motor does not require a reduction gearbox to reach full efficiency at cruising RPM, meaning greater efficiency, longevity and near-silent operation.
A magnetic coupling conveys the torque from the motor through the hull to the drive shaft connecting the propeller. A magnetic coupling using rare-earth magnets provides several advantages over a typical shaft seal including indefinite longevity, almost no friction, and no chance of leaking since there is no hole in the hull.
We have tested our drive system with a full-sized 24’ prototype, and results indicate that our vessel will move at our target speed of four knots with just under 100 watts input. With a solar array of 1200 watts and a LiPo battery system, the vessel should have no problem outputting at least 100 watts continuously in spring, summer and fall conditions. The vessel can move at speeds of up to seven knots for shorter periods. The motor and drive system are designed to run in excess of 10,000 hours between servicing.
A solar-powered boat has several advantages beyond speed over other forms (such as sail, wave and use of thermal gradient) of renewable energy. Maneuverability and speed control are much more precise, allowing the vessel to be used in congested waterways such as harbors, and to stay precisely on waypoints for data collection. Additionally, the energy can be stored in batteries allowing for precise rationing and consumption of available power as required.
The vessel is engineered to cope with sea conditions exceeding hurricane force, and it self rights instantly. The self-righting system is a passive design, offering infallible reliability.