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49 USVs | Insight designed as a system of replaceable cartridges or ‘pods’. That means it can be modular in terms of its carrying capacity for systems such as payloads, avionics or power banks. The Accession also has a reverse-bow design, a shape increasingly adopted by vessels for heavy weather, to make it more stable when taking images of coasts, seafloors or marine infrastructure. “You can have a bespoke length of, say, 3.5 m, and then the stern detaches and you can integrate an extra 75 cm or 150 cm length of hull,” says James Williams, director of USS and managing director of Swathe Services, which supplies maritime survey technologies. “As well as more batteries or payloads, users can add a diesel generator to ramp up their Accession’s endurance. As a result, the 3.5 m version runs for about 12 hours as standard, the 5 m version for about eight days. “Also, if required, a user could obtain just one USV and then half-a-dozen different payloads through Swathe Services, which they’ll be able to use in any combination of as many or as few as they want,” Williams says. The company’s method for joining the USV’s different sections is currently proprietary and cannot be disclosed, but Williams says it should take survey operators roughly 30 minutes to replace a mid-section of the vessel if a different operation needs to be carried out. That would include unplugging the USB connections for power, as well as Ethernet connections for data, but otherwise the pods are designed as turnkey systems. In operation, the main system batteries can be recharged while the mid-section is swapped out. The USV has largely been designed to work as a force multiplier with a mothership such as a 12 m port authority catamaran, or a bigger vessel needing a more nimble, long- endurance survey tool. As well as providing a high degree of payload modularity and thus a range of survey possibilities, the company sees a major application of the craft as a launch- and-recovery platform for UAVs. “Swathe Services also represents Planck Aerosystems, which has developed the capability to launch and recover UAVs from moving platforms, whether that’s flatbeds or UGVs on land or boats, or USVs in motion across water,” Williams explains (and as featured in UST 25, April/May 2019). “The US military is taking great interest in that platform, and even looking into developing tethered versions, and we are integrating Planck’s Shearwater UAS into our USV to provide an unmanned force multiplier across air and sea.” That might also include integrating a UAV charging station into a future mid- section pod of the Accession, potentially to charge the Shearwater from the onboard diesel generator. “Of the nine months we spent on developing the craft, most of that time was spent on modelling, to place sensor combinations sensibly and prevent bubble-wash – which can harm sensor performance on a lot of USV designs, especially sonars – and to ensure that we had the design right before building the moulds for bulk production.” Unmanned Systems Technology | June/July 2019 The Accession USV is made from three detachable sections, with the middle part customisable across different sizing options If required, a user could obtain just one USV and then use several different payloads in any combination – as few or as many