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47 to its target at speeds of up to 28 mph. Emily is tethered to its origin and once it has made contact, having ropes on each side it can pull the survivor back to shore or will give them something to hold on to until a rescuer arrives. It has loudspeakers so that the lifeguard navigating it can give instructions to the person being rescued. It also has a sonar device that can scan for underwater movements associated with distressed swimmers. Having established Emily in the marketplace in 2009, Hydronalix has gone on to develop an untethered autonomous mobile buoy (AMB) on essentially the same platform using Piccolo autopilot technology for navigation via satellite link. Initially still electrically powered, the latest development has been to use an internal combustion (IC) engine, as described here. An IC power unit is inherently heavier but this engine was developed to increase the buoy’s endurance. With this it is intended to support missions ranging from search and rescue, bathymetric mapping and underwater ISR (intelligence, surveillance and reconnaissance), to meteorological station keeping and data gathering, even in challenging marine environments. The IC-engined AMB is equipped with sensors that include three types of sonar, a weather station and X-band radar. It is designed to loiter in a certain place for a very long time, sometimes for a period of months. It will sit and drift, and when it drifts to a certain point it will start its engine to power back to its original location. It thus stays in the general area assigned to it. Indeed, the AMB is sometimes dropped into the (still water) eye of a hurricane, being programmed to follow its movement, collecting data. The requirement The AMB’s IC engine is used for electrical power generation and, once in position, station keeping. Normally the buoy travels slowly, at around 3 knots. Part of the brief was that the engine has to start and stop autonomously rather than under remote control. The brief from Hydronalix was also for a light and fuel-efficient engine of at least 2 bhp that radiated so little heat it wouldn’t heat the buoy’s engine compartment by more than 10 F above ambient temperature. Engine emissions were another concern since the buoy is intended to operate in a marine sanctuary environment, and its exhaust needs to be discharged under water. Thus the engine also had to be clean burn and EPA-compliant. The brief was also for the engine to be durable enough to run 1000 hours or more between overhauls. It also had to be as light as possible to help the craft get up on plane when required to move swiftly. There is a standard rail system in the buoy that allows the power unit to be switched between this one and an all- electric drive. It follows that the IC engine power unit had to fit the same envelope as an existing electrically driven version. The battery box of the electrical version was replaced by the fuel tank, and the IC power unit was then engineered into the space available within the vee (cross- section) hull. “We exploited every nook and cranny to accommodate the engine oil pan, the water pump and so on; it is all tightly arranged and conforms to the shape of the vehicle,” notes HFE’s Tom West, lead designer of this power unit, the H70. Since the H70’s location was predetermined by the design of the existing electrically driven version, much of the unit sits below the waterline. That has the advantage of keeping the centre of gravity low, assisting the self-righting capability of the buoy. It also brings challenges, as we shall see. HFE H70 marine powertrain | Dossier Unmanned Systems Technology | October/November 2016 We exploited every nook and cranny; the engine oil pan and so on are all tightly arranged to conform to the vehicle’s shape The H70-powered autonomous mobile buoy as used by the Los Angeles County Fire Department Lifeguards