SeaCAT and the SeaClear project | In operation biofuels, but finds them insufficiently carbon-neutral in their planting and processing stages, and their lower energy density compared with diesel poses another drawback. Back ashore Once a coastal sweep is done, the SeaCAT is designed to be lifted by standard harbour cranes and stowed on a ship or quay with a four-point mooring system. Ideally however it should be hoisted directly onto the rails of its container and cleaned with a powerful freshwater hose to prevent fouling or corrosion from seawater. The infrastructure for the Mini Tortuga and DJI 210 can then be dismantled, the navigation masts can be folded down, and all systems can be stowed in their containers. Overall, the recovery, cleaning and disassembly takes about 2 hours. SeaClear Phase Two The second phase of SeaClear began in January, with the first phase set to conclude at the end of this year, after further public demonstrations this October when the consortium returns to Dubrovnik, so technically there is a oneyear overlap between the two phases. The second phase is aimed at improving various performance aspects across the autonomous ecosystem. To that end, a USV like the SeaCAT but larger and with integrated solar power is in the works. On that USV, the stern ROV will be replaced with a smart grappling arm to be designed by the Technical University of Munich and equipped with sensors and thrusters, which will increase the weight capacity per lift to 250 kg. That means objects too large and heavy for the Tortuga or professional divers can now be removed from the sea, such as discarded household appliances, industrial vehicle tyres and motorbikes. An A-frame and winch will lift and lower the smart grappler to grab waste from up to 300 m below the surface. “Also, the larger USV will be paired with a much smaller USV we’re working on, which we’ve called the Tender Shuttle,” Chardard explains. “It will be hydrogen-electric, and its job will be to go back and forth between shore and mothership, taking the litter loads from the large USV and transporting them to coastal sanitation workers.” For the company’s purposes, having a hydrogen fuel cell and bottles of hydrogen gas on the Tender Shuttle makes sense, as it is to be a small USV with a small powertrain, one that is relatively inexpensive compared to the size of fuel cell and hydrogen storage that the SeaCAT or its larger successor would need. The Shuttle’s frequent trips back to shore also dictate an energy storage system that can be quickly replenished, so the hydrogen bottles can be replaced and refilled within a few minutes. With all these changes to the operation, Subsea Tech expects that about 20002500 kg of litter will be collected each day. “One thing I want to add is that we didn’t want to collect surface litter during phase 1 of SeaClear, as there are small USVs and static systems that already do that, but in phase 2 we’ll add that capability,” Chardard comments. “We’ll hang a frame and net with room for 500-1000 kg of litter between the inflatable hulls, and the catamaran will sail over floating litter, making for a more complete cleaning solution.” At the time of writing, Subsea Tech had the capacity to produce up to five SeaCATs a year, although it was confident it would find and partner with as many subcontractors as needed should more of the USVs be required for SeaClear, similar research projects or organisations who want to take on the project’s concept on a more industrial scale. 63 Uncrewed Systems Technology | October/November 2023 SeaCAT USV Catamaran with rigid inflatable hulls Diesel-electric hybrid Dimensions (inflated): 6.83 x 3.1 x 2.15 m Dimensions (inflated): 5.78 x 2.15 x 2.15 m Weight: 1075 kg without payload Maximum payload: 500 kg Maximum speed: 6 knots Maximum sea state: 4 during operations, 6 during transit Some key suppliers Diesel engine-generator: Kubota Thrusters: Fischer Panda Coordination intelligence software: Fraunhofer USBL: Blueprint Subsea USBL: Applied Acoustics Imaging sonar: Blueprint Subsea Single-beam bathymetry sonar: Airmar Multi-beam bathymetry sonar: Norbit 3D Lidar: Norbit or Velodyne Specifications Litter picked by the Tortuga is deposited in a cage deployed on the seafloor by the SeaCAT at the start of operations
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