Centralised control of Pioneer’s functions rests with two main computers. The first is ACUA’s C5 module, which is Linux-based and connects via four different CAN buses to most subsystems. It runs ACUA’s proprietary remote software (built around a NATS infrastructure-based middleware), and is passively air-cooled to avoid adding surplus motors and pumps. The other main computer is the powertrain control unit delivered via Robosys Automation, which is a Windows-based system running a bespoke derivative of Robosys’ AI Survey software and connecting to the various powertrain components via a dual redundant CAN bus. Moon pool The moon pool is designed with mounting points for standard ISO blocking arrangements, enabling anyone with an ISO container or payload they would like to install in Pioneer to pull up the ISO standards, find the spacing and adopt it to drop their system into the moon pool (including mechanisms for lowering payloads, ROVs and so on into the water, as well as retracting or recovering them similarly afterwards). “As Pioneer is mostly aluminium, the degree of aluminium needed to support ISO containers across the span of the moon pool would’ve been enormous, so we built the mounting booms from steel, which in turn means a galvanic mismatch because now there’s aluminium and steel in contact,” Mulcahy says. “But, once you recognise the problem, it’s just a matter of using appropriate galvanic isolation and protection measures, such as rubber sheeting or other materials, as well as a shorter maintenance survey interval to make sure the mitigation is holding up.” Detailed FEA simulations and studies have helped understanding and design optimisation of how loads carried in the moon pool are transmitted through the hull, as well as affirming that weight significantly exceeding the 6.5 t payload capacity can be handled by the structure amid extremes of sea states and movements in all three axes (wave-tank testing having played a key role here). “At the back end of the frontal transverse beam there’s an empty gland – a fire-rated, pressure-rated, gas-tight frame provided by Roxtec for wire management in a sealed manner through bulkheads – which can be used to electrically connect payloads to the forward electrical rack, with space and weight provision for up to three racks of equipment, such as computers for running payload systems,” says Mulcahy. Hydrogen systems ACUA Ocean’s initial approach for the storage and delivery of hydrogen will involve placing a hydrogen storage unit in the aft region of the central moon pool area. The unit is a modular frame that can hold up to nine cylinders of H2 stored at 350 bar (each cylinder holding up to 10 kg or 333 kWh of hydrogen gas), although just three cylinders are installed for the first sea trials. Gas travels from the module via a connection through the starboard-aft quarter to the fuel-cell supply valve, entering the fuel cell at approximately 7-8 bar; that fuel cell being a bespoke unit from US-based Nuvera. “Fuel cells are well-established among automotive groups like Hyundai and Toyota, but the marine context is very different from the automotive context, and it’s hard to find maritime fuel cells outside of giant, megawatt-level systems way oversized for our needs,” Anuyagu says. “Nuvera were very open to our concept, and the 45 kW net power output of our fuel cell fits our power delivery needs exactly, giving us plenty of capacity for extra payload systems in the future. Their tech is also very efficient, hitting 58% thermal efficiency, whereas most fuel cells are still only doing 50-52% at best.” Batteries and electrics The two main battery packs are Kreizel units, running on 21700-type, lithiumion, cylindrical cells, with each pack containing up to 63 kWh and providing a 400 V supply to the powertrain. “They’re very high-performance batteries, and I consider them equivalent to motorsport-level systems I’ve seen. For example, they can discharge up to 250 kW for 10 seconds, which can be useful in certain emergency or application-specific contexts, but most important to us is their 400 V DC bus and that their modularity enables them to be strung together in groups of many,” Anuyagu says. Dossier | ACUA Ocean Pioneer-class H-USV 34 February/March 2025 | Uncrewed Systems Technology Trident Marine was key in designing the electrical network, which is managed via a dedicated PLC; a straightforward system running reliable programming languages, certified under IEC 61508
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