66 Staying durable Naturally, the USV’s long endurance at sea depends not just on robust power but also on a strong hull, and Seasats has chosen a particular fibreglass-epoxy composite for Lightfish’s outer shell – a durable and lightweight material ideal for weathering ocean environments, as well as an easier choice than aluminium if the USV were to remain portable for hand carrying and launching. “The marine environment is a really hard thing to deal with. There are hydrostatic loads and hydrodynamic loads, both of which can be very difficult to predict, and so we went through several iterations on the USV’s hull structure, as well as the subsystems before reaching our current design,” Kramers says. As for ensuring subsystem survival against the ravages of the ocean, Rodriguez adds: “The last company I worked at was Ocean Aero [featured in Issue 9] for five years. That platform was submersible and an amazing piece of engineering, but if you make something submersible, you make it expensive and hard to disassemble. “Engineering is often a series of compromises, and with the Lightfish there’s been some optimisation that we’ve worked very hard on, so that all the subsystems are sufficiently water-proofed, but not a huge pain to take apart and not expensive.” Selection and testing of sealing solutions formed much of the company’s optimisations. Within the Seasats office one can find a two-storey, vertically disposed PVC pipe, which the team will periodically fill with salt or fresh water for high-pressure submergence testing of different housings and sealing agents (as well as key components such as marine connectors). “That pipe has proven its worth with the USV’s non-submerged components too. We’ve found antennas whose manufacturers advertise them as IP68, but they aren’t at all able to survive up to 30 minutes in 1.5 m depths of fresh water in the PVC pipe, which ‘IP68-rated’ is supposed to mean,” Rodriguez explains. “It might sound like an exhaustive level of testing, but you can see that without it we could’ve sent 20 boats around the world that were doomed to lose their comms links as soon as they got rolled over by waves for the first time.” In addition to the chemical hazards of the ocean, biological hazards are also a perennial concern for persistent maritime platforms. While many anti-biofouling approaches exist, Seasats has opted April/May 2025 | Uncrewed Systems Technology Extensive submergence testing has been performed to ensure the USV’s components can survive being rolled or temporarily submerged by Pacific waves As an added layer of GNSS-spoofing and -jamming safety, the Lightfish embeds the same physics model as the company’s simulator, enabling it to measure its movements against claims made by the GNSS data
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