Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

88 A daptability through modularity was central to Unmanned Survey Solutions’ concept for its Accession Class USV. The craft can be operated in its 3.5 m-long base version, or extended to 4.25 or 5 m by inserting a modular hull section either 0.75 or 1.5 m long. Equipped with combinations of extra payload and diesel fuel, these modules increase the USV’s endurance from 12 hours with a DC-only version at typical hydrographic survey speeds, to up to 20 days for a hybrid version. All the hull sections are independently watertight, buoyant and fitted with bilge pumps. They are built from glass- reinforced plastic, the structure consisting of resin-infused laminates forming two skins separated by a core. We caught up with company director James Williams and his team at the Ocean Business 2022 show in mid- March, where they were demonstrating the pre-production vessel in its Accession 425 configuration with the 0.75 m central hull module. The USV’s hull is designed to USS’ specifications by Jack Gifford Marine Design. “I’m not a naval architect, I’m a hydrographic surveyor, and I use that expertise to create a design brief for the architect,” Williams says. “The final design then goes to a professional boat builder, who builds the bare hulls. These then come to us, where we fit them out with everything from command & control systems to sensor payloads.” The propulsion system is a series- hybrid configuration, with a diesel generator to charge the lithium-ion battery pack and powering electric thrusters directly. There is also an onboard charger so that the boat can plug into shore power to top up the batteries when required. Functional sections The vessel is arranged in functional sections from bow to stern. The forward section has a detachable beak, behind which is a watertight hatch over the compartment housing the command & control systems, the power management system, the dual 4G modem and all the wi- fi equipment, with the batteries underneath. A set of back-up batteries is kept charged by a solar panel for redundancy. Williams says, “In the event of losing primary power to the boat, we can establish contact through a separate Iridium installation and tell the boat to restart and boot up.” The compartment containing this equipment is divided from the rest of the forward section by a vertical bulkhead, aft of which is the diesel generator and two hull- skin fuel tanks that hold about 170 litres. Aft of the 0.75 m hull module, which houses payload equipment, is the stern section that supports a pair of steerable DC electric thrusters, although there is no rudder. “We wanted both azimuth steering and variable thrust, so that if we lose one thruster we can still manoeuvre the boat,” Williams says. “We can turn one to the left and run it in reverse and the other to the right and run it forwards, so that the boat can do a 360 º turn on the spot. She is highly manoeuvrable in close conditions.” Good sea-keeping qualities are vital for survey vessels, a requirement that drove a couple of distinctive aspects of the hull design. “She has a reverse bow, so Whether it’s Port Authority operations or offshore surveys, this modular USV can handle it. Peter Donaldson looks at its development Multiple choice June/July 2022 | Uncrewed Systems Technology