Unmanned Systems Technology 027 l Hummingbird XRP l Gimbals l UAVs insight l AUVSI report part 2 l O’Neill Power Systems NorEaster l Kratos Defense ATMA l Performance Monitoring l Kongsberg Maritime Sounder

94 The forwardmost and rearmost hatches are simple storage compartments, where ropes and other mooring equipment can be stowed if desired. As well as providing the moonpool, the design and manufacturing teams at Kongsberg can mould sensor payloads directly into the fibreglass of the hull if requested. Also, inside the bow area, a steel backing plate is fixed onto the inner fibreglass layer. The plate can be used to mount additional payloads if a user wants to collect data at the front of the craft, without having to lower a particular sensor into the water. These would then be connected through to the Sounder’s power system, or they might use their own separate battery if enough space had been left on the plate. As well as being compatible with such systems as Kongsberg’s various multi- beam echo sounders (and other sonar- based imaging sensors), the Sounder can also use the Simrad SX90 low- frequency omni-directional fishery sonar. This cylindrical transducer transmits sound waves 360° horizontally around the boat, and is programmed to generate radar-like imagery of the direction, distance and size of schools of fish. The first Sounder with an SX90 has been sold to TASA, the largest fishing company in Peru. It will be used to look for large groups of fish up to 2 km away from the USV, and can be combined with a downward-facing echo sounder. After navigating to above a given school of fish, that will enable the Sounder to take acoustic measurements inside and around the school to determine the school’s size distribution. Based on the general size of the fish, the crews operating the Sounder will then be able to determine whether the school should be tracked down and hauled in by a trawler, or whether it should be left to mature in favour of another catch. Propulsion The Sounder has a maximum speed of 12 knots, while the recommended operating speed is from 4 to 8 knots. Up to 20 days of endurance can be achieved if operations are typically run at 4 knots. Propulsion is delivered by a single fixed-pitch propeller, powered by a Steyr SE 126E25 diesel engine. Selecting this particular engine rested on a number of considerations by both Norsafe and Kongsberg. “We wanted to keep the propulsion as simple as possible in how it operates, using a marine engine that would be familiar to operators and technicians in hydrographics, mine countermeasures, fishery surveys and other applications for which the Sounder is intended,” Kristoffersen explains. The Steyr SE 126E25 is a four-stroke, turbocharged six-cylinder engine. Each cylinder has a bore of 85 mm and a 94 mm stroke, for a total displacement of 3.2 litres. It uses direct injection, has a top operating speed of 2500 rpm, produces a maximum torque of 390 Nm at 1800 rpm, and a dry weight of 340 kg. While the design team’s targets for speed and endurance could have been satisfied by a smaller, four-cylinder engine, they went with the straight-six Steyr as it produces less vibration than the four-cylinder models that matched the mission envelope. Less vibration naturally means fewer blurs in the survey imagery. The engine also has a lower specific fuel consumption between 4 and 8 knots than the four-cylinder marine engines that were investigated, so the relatively larger engine was selected to aid endurance and fuel efficiency. As the propeller is fixed pitch, no gearing is used to rotate the angles of the prop blades; instead the speed is linked to engine rpm. The drivetrain comes with a separate marine gearbox to provide the transmission for running the propeller at operating speeds and maximum speed. “We experimented a bit with different propeller sizes, iterating with different versions to achieve the optimum endurance with that engine set-up,” Kristoffersen says. Norsafe’s emphasis on choosing the Steyr six-cylinder also came from it being a SOLAS engine: this is a standard for maritime use that enables automatic shutdown (therefore helping platform stability) among other things if the Sounder should accidentally flip to 90 º . Once it rights itself, the oil settles and the engine can be restarted. A generator has been mounted on the engine’s flywheel to power the various onboard computers, sensors and other systems. It produces up to 4 kW, although that can be increased if requested. August/September 2019 | Unmanned Systems Technology The Sounder’s propulsion uses a Steyr six- cylinder diesel engine to drive a single fixed-pitch propeller. Steering is provided by three rudders