Unmanned Systems Technology 033 l SubSeaSail Gen6 USSV l Servo actuators focus l UAVs insight l Farnborough 2020 update l Transforma XDBOT l Strange Development REVolution l Radio telemetry focus

25 S ubSeaSail’s sixth-generation unmanned sailing vessel has an unusual configuration that places most of it under the surface. This enables it to keep acoustic sensors clear of wave noise, leaving only the wingsail and a small section of the flotation module that supports it above the surface, where they provide space for comms components, small payloads and solar panels. Described by the company as an unmanned semi-submersible vessel (USSV), it is now in service with its first customer and is also offered for missions in the realm of ocean science and defence, including weather and water monitoring, surveillance, intrusion detection and even cargo delivery. Some versions will have the option of submerging completely to avoid bad weather, collision or hostile interference. The original concept came from a requirement issued by the US National Oceanographic and Atmospheric Administration for a way to move small ‘daughter’ UUVs long distances and release them for limited-life missions. The concept was subsequently greatly expanded, and the initial patent went from eight claims to more than 20 that conceived a series of sizes and forms for the USSV. The Gen6’s main hull is a streamlined cylindrical body connected to the flotation body by two members that form a triangle with the float at the apex and the hull at the base. The forward member is the structural keel, while the post around which the rudder pivots forms the after-member. “Pushing a streamlined body through the water produces less drag than the same volume would on the surface, because you don’t have to generate a wave train,” SubSeaSail’s co-founder and lead technical partner Chris Todter explains. “You have friction and viscous drag, but not wave-making drag, so you can get away with substantially less power from the sail, in turn reducing its size and complexity.” The wingsail is supported on the flotation module (buoyancy section) by a static mast, at the top of which lightweight antennas, cameras and lights can be mounted. Pivoting freely around the mast, the sail is hollow, transparent and floodable, and needs no powered actuation. Transparent materials are used for the wingsail because several potential customers envisaged applications in which low observability in terms of visual, radar and thermal signatures was important. The wingsail is open at the SubSeaSail Gen6 USSV | Dossier Solar power generation and wingsail propulsion give this semi- submersible practically unlimited endurance. Peter Donaldson reports on how it was conceived and developed Sailing orders You have friction and viscous drag but not wave- making drag, so you need much less power from the sail, reducing its complexity Unmanned Systems Technology | August/September 2020