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23 The Sabertooth is available in single- and double-hull configurations; this article is focused on the latter. With a launch weight of between 1200 and 1500 kg, the largest configuration of it has a length of nearly 4.1 m and a height of 67 cm. Its 30 kW/h battery capacity offers an endurance of more than 14 hours and a maximum forward speed of 4 knots on the 100 kgf generated by a pair of rear- mounted thrusters. There is also a lateral tunnel thruster capable of generating 90 kgf and three vertically mounted thrusters rated at 160 kgf. Using these in combination, the control system provides the vehicle with complete freedom of manoeuvre about the three rotational and three translational axes. The vehicle can be ordered with depth ratings of 1200 or 3000 m. Operating near the sea floor in close proximity to the infrastructure and equipment of the offshore energy industry demands high levels of ruggedness and reliability, Siesjo emphasises. He adds that Saab drew on its experience of building traditional ROVs to achieve that, using as many proven components as possible. As with all its underwater vehicles, the company also turned to its iCON technology platform, described as a network of distributed devices and software. It consists of building blocks for vehicle control, navigation and behaviours, maintenance management and power distribution. “Essentially, iCON is our component box that we try to re- use whether we are building an ROV or an AUV,” Siesjo says. Range versus manipulation In terms of its overall shape, the Sabertooth lies between two stereotypical extremes of the torpedo-like AUV and the boxy ROV. “Torpedo-shaped vehicles are nice because they have very low drag and so can go long distances on a small battery, but they are terrible when it comes to interacting with something,” Siesjo says. “They can swim around with scanning sensors, but they can’t really manipulate anything. “The other end of the spectrum are the traditional ROVs. They look like big boxes with propellers on the corners, and are terrible from a hydrodynamic point of view but are very manoeuvrable and great for manipulating things.” The requirement for the Sabertooth was for a vehicle that could swim out from a ship or docking station to a work site, so a reasonable range was essential. Then, once it reached its destination, it would need the manoeuvrability, stability and fine control to stop at the right spot and deploy sensors or tools. “What you end up with is basically a flatter, slimmer ROV redesigned to operate on battery power,” Siesjo says. The primary structure is made from ASTM A4-grade stainless steel, and takes the form of a backbone with outriggers. A lifting eye for launch & recovery is attached to the middle of the backbone at the vehicle’s nominal point of balance. On either side of the backbone is an ‘e-pod’ containing the pressure hulls that protect the battery packs, power conditioning electronics, computers, Saab Sabertooth AUV | Dossier Torpedo-shaped vehicles are nice because they have very low drag, but they are terrible when they interact with something Unmanned Systems Technology | February/March 2021 The Sabertooth was developed to spend long periods close to the sea floor, minimising the use of expensive support ships for launch & recovery (Courtesy of Saab)