63 “The automatic collection is done by mechanical grippers,” Chardard adds. “And the CONOPS for navigation is initially for a general back-and-forth lawnmower pattern across the area to be cleaned. “The Mini Tortuga’s mapping and litter detection is delivered by umbilical tethers to the SeaCAT, so the mothership can deviate fromwaypoints to seek out and prioritise its collection.” Subsea Tech intends that the Tortuga should move faster than the Mini Tortuga, so that the former can more easily dart about collecting litter while the latter maps and scans with a slower, more stable motion. In situations where the density of litter is toomuch for the Tortuga to collect while keeping up with the SeaCAT andMini Tortuga, it becomes the primary navigation arbitrator, and the other two systems slow tomatch the Tortuga’s pace. As well as serving as the launch, storage and recovery platform for the ROVs, the SeaCAT is also their power source and the central ‘brain’ of the solution. All the control software for the ROVs is embedded in the SeaCAT’s computer, with commands transmitted down – and underwater sensor data transmitted up – via the tethers. “We supervised all three vehicles over 5 GHz wi-fi from a shore station, but all the autonomy was inside the SeaCAT,” Chardard notes. “We deployed a UAV from the SeaCAT for aerial litter detection on the surface or through very clear waters, and also for long-distance navigational safety; it can see incoming ships much further away as well.” The SeaCAT has an empty weight of 1075 kg and a 500 kg payload capacity. It is powered by a 12 kW diesel generator with up to 400 litres of fuel on board, and two unidirectional Aziprop electric thrusters for propulsion, enabling it to transit safely through sea states up to level 5. A system of electrical winches and tilting baskets enabled the launch, recovery and storage of the ROVs, with up to 300 m deployment range for the Tortuga and Mini. A 40 m tether powered the UAV, a DJI Matrice M210 RTK. USVs | Insight Uncrewed Systems Technology | June/July 2023 In the EU SeaClear project a SeaCAT USV from Subsea Tech has been cleaning refuse from seabeds, deploying a UAV to survey for litter and two ROVs to collect it (Courtesy of Subsea Tech) Zelim is constructing the nextgeneration version of its Guardian USV, refining its fully uncrewed search & rescue capabilities (Courtesy of Zelim)
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