Hull balancing Zero has distributed Oceanus12’s subsystems across its structure, principally to maintain the centres of gravity and buoyancy, thereby minimising the degree of pitching caused by payload mass and making the vessel’s trim as easy to control as possible. “There is a collision bulkhead right at the front, with a fairly large void space behind that is going to carry quite a bit of electronics and computer power, as well as two day tanks,” Ratsey explains. The fuel system has two main tanks, collectively storing 750 litres of diesel, which pump into two day tanks of 100 litres each. The generators then draw fuel from the day tanks. This approach reduces the risk of fuel being contaminated (by water or another substance) in the main tanks and those contaminants reaching the powertrain. “Further back, we reach the main mid-section in which you see there’s two generators – one each side, port and starboard, as well as a fuel tank each side,” Ratsey says. “We also have our battery chargers and motor inverters in that section. “Then there’s another bulkhead, beyond which the boat splits into a payload deck above and a battery deck below, and then behind those we’ve got the RAD electric drives. They are a little bit like Volvo IPS drives; their shafts are able to rotate 180° and they can run in forward or reverse mode. That gives an effective, 360° rotation capability and also makes them somewhat like azipod thrusters, though with azipods you can rotate 360° but you don’t get a reverse-thrust setting – you just have to rotate 180° and thrust forwards, whereas we can do both and we get the same effect.” Beneath the vessel, the keel functions as a sensor strut, integrating survey payloads below the waterline, as well as cooling systems. While Zero was tempted to use the Mayflower’s pumped-seawater cooling approach, a conventional, closedloop, water-glycol arrangement was found to bring greater reliability than the former’s impellers or raw water pumps. “Since we needed a functioning water-glycol system onboard for our batteries and some other systems anyway, it made sense to share it among the other systems,” Ratsey notes. Maritime electronics Above deck, an A-frame arrangement houses sensors for the autonomy system. As well as cameras, W-band and X-band radars are installed. The former detects objects at normal amplitude and distance, while the latter gives close-up, high-definition resolution data. The radars were chosen over Lidar as the latter induces reflections and hence distorted images off almost any source of water, including waves, rain or splashes. Radar, by contrast, will operate in any realistic environmental condition. “Range is a key distinguisher. Radars provide for great obstacle detection at long range, whereas even with highquality Lidar you’ll struggle to get more than 200 m out of them,” Ratsey says. A Simrad HALO20+ device serves as the W-band radar, purchased COTS but tuned to function with Zero’s autonomy software. The hi-res X-band system, supplied by NavTech, can distinguish between fishing traps, small mooring buoys and swimmers within 1000 m of the USV. “It allows us to navigate among closerange objects, giving 3D information correlating very strongly with what we’re seeing on the cameras, and possibly of superior value over the vision data if visibility is poor,” Ratsey says. The cameras are COTS bullet-type cameras from IRIS, selected for their cost-effectiveness and field of view, by which five units installed concentrically around the USV give 360° visibility. 111 Uncrewed Systems Technology | October/November 2024 Subsystems are distributed across the USV to maintain the centres of gravity and buoyancy, and hence minimise pitching induced by payload mass An A-frame arrangement is designed to sit atop the USV for housing sensors key to the autonomy system – specifically, cameras, W-band radars and X-band radars
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