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31 five-axis CNC machine. The mould splits to allow the finished hull to be extracted. The top comes off and the sides come away, and it is possible to see the split lines on the finished part. Before the mould goes into the roto-moulding machine, it is fitted with stainless steel inserts to provide holes to which other components can be attached during integration and assembly of the vehicle. Some inserts are threaded and simply provide local attachment points, while others, for example those to which the cross-beams attach, are tubes that take the compression loads associated with through-bolting. GRP gondola The gondola is a glass reinforced plastic (GRP) moulding that ASV lays up in its own lamination facility, while the cross- deck beams that connect the hulls and to which the gondola is mounted are 6061 aluminium alloy extrusions, which are anodised for aesthetic reasons. The company considered making the hulls in GRP, which would have saved weight, but polyethylene’s toughness won the day. “It’s the gondola you should be taking care of, because it contains all your expensive equipment,” Daltry says. “It is above the water and it won’t ever touch the beach, so we were happy to make that in GRP for the weight benefit.” The company keeps several manufacturing operations in-house. It designs and fabricates the aluminium components, populates some of its own printed circuit boards and produces all of the wiring system apart from any that comes with subsystems it has bought in, such as the motor controller and propulsion drives. At heart, however, ASV has come to view itself as a control systems company that makes unmanned boats. “We very much started off doing boats, but our engineering team is dominated now by software and electronics people,” Daltry says. “We have a team of nine naval architects and mechanical designers who do the boat designs, but we have 40-odd software and electronics people.” Energy and power The C-Cat 3’s energy budget is predicated on the need to do a full day’s work with the associated propulsion, payload, control and comms loads. As much of the boat’s work will be carried out in relatively shallow water, this will enable operators to use very high-frequency multi-beam sonars, which Daltry points out are nothing like as power-hungry as those used for some of ASV’s previous applications. “We have done a lot of work with the bigger USVs in water up to 200 m deep, and you end up with several hundred Watts of payload running,” he says. “In the C-Cat 3’s case a lot of the payloads run on less than 100 W, although the boat will support more powerful sonars. There is also volume and payload to spare for extra batteries to power sensors or other equipment if the operator needs them.” Almost all the power and propulsion system is bought off the shelf from Torqeedo, a well-known marine electric propulsion supplier. Components include the lithium-ion batteries, the thrusters Unmanned Systems Technology | February/March 2018 ASV Global C-Cat 3 USV | Dossier The lithium-ion batteries include an integrated battery management system, a waterproof pressure equalisation membrane, water sensors and waterproof cabling (Courtesy of Torqeedo)