36 Dossier | ACUA Ocean Pioneer-class H-USV creates more heat than the vessel in operation,” Anuyagu says. “Each battery has its own primary, water-glycol cooling loop, which connects to a dedicated heat exchanger and a wider vessel-cooling loop; the latter, wider loop rejecting heat via a keel cooler.” As of writing, the keel cooler is scaled for optimal performance in sea water temperatures of 20 C (globally, they rarely exceed 25 C), but such is the thermal headroom of the two primary cooling loops that the keel cooling loop will mainly be needed when customers are maxing out the power consumption of the onboard subsystems. “Modularity depends on a solid foundation for the modular ‘Lego blocks’ to be stacked upon, and the cooling systems are a big part of that foundation in that they’re not modular, they’re rigid, and they’ll stay as they are because they’re what allow us to put the various other systems onboard,” Anuyagu says. Thrusters Through early system-wide analysis, Mulcahy identified the propeller as the highest potential source of efficiency losses: a 50% efficiency rate is typical with a decent propeller, whereas most onboard electrical and electronics perform with over 90% efficiency. “Hence, I focused on finding something highly efficient at the speed we picked, and we picked it on the basis of ‘must, should and could’. Our ‘must’ was 4 knots, our ‘should’ was 6 knots and our ‘could’ was 8 knots,” he recounts. It soon became clear that fixating on 4 knots and striving for 6 knots would be suitable for Pioneer’s drivetrain. After researching market solutions, ACUA Ocean decided that CJR Propulsion understood its requirements and matched its speed profile with a highly efficient propeller design, borne out of hundreds of simulation runs and manual adjustments of simulation models. “Then, CJR made use of an incredibly well-refined manufacturing process, heavily utilising robotics first to cut the moulds before they’re used for casting the propeller parts in a foundry,” Mulcahy says. “The rough-cast elements that come out of that are already quite precise, because they’ve been produced by Kuka robots in CJR’s factory, but they’re then put into a five-axis CNC machine and milled down to an incredibly precise and hydrodynamic finish. That gives us a propeller that is just over 70% efficient, which has very dramatic benefits for the endurance of the vessel, potentially making the difference of tens of days of endurance, depending on the type and quantity of fuel.” Forward from each propeller is a standard assembly of propeller shafts with thrust bearings and stern seals. The propulsion assembly enables differential thrust, with a 9 m beam that enables February/March 2025 | Uncrewed Systems Technology ACUA’s modular manufacturing approach stands to reduce vessel lead times by years, while the stability of SWATHs in high sea states could double the industry’s permitted survey days per year The propellers from CJR were designed, manufactured and finished to achieve just over 70% efficiency, adding potentially tens of days to Pioneer’s maximum endurance
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