Issue 39 Unmanned Systems Technology August/September 2021 Maritime Robotics Mariner l Simulation tools focus l MRS MR-10 and MR-20 l UAVs insight l HFE International GenPod l Exotec Skypod l Autopilots focus l Aquaai Mazu

26 integrated into the harness and fixed to the internal structure. When the decision on whether to do that was being debated, the issue of the impression its appearance would make on customers came up. According to Hovstein, the worry was that it didn’t look expensive enough, so the team pondered whether they should put the computer in a nicer-looking box. “But the practical solution won,” he says. Maritime Robotics recommends that customers invest in a spare to avoid downtime, but none has yet taken up this option, Hovstein adds. “We take this as a good sign in terms of proven uptime.” Perhaps surprisingly, water jet propulsion is another example. Often associated with high-speed vessels and marginal efficiency at low speeds, water jets are nonetheless well-liked by seismic survey operators, Hovstein notes, because it is the option that gives them the most uptime and is safer than a conventional propeller for anyone who is in the water at the same time and is less prone to becoming clogged. Kristoffer Fortun, the company’s chief sales officer, points out that a propeller is normally the lowest point of a vessel, while the water jet intake is flush with the hull and the bucket does not protrude below it. He also emphasises that controllability is not a problem. “We have excellent line-tracking software, and we don’t see any issues with using water jets at low speeds,” he says. Propulsion and back-up Mariner’s prime source of propulsion is a 195 bhp Yanmar diesel engine that is mechanically coupled to the water jet, from Hamilton, which has a steerable bucket. Alternatively, the water jet can be driven for short periods by a battery- powered electric motor. There is also a back-up propulsion system consisting of a pair of stern-mounted electric thrusters and a bow thruster from Torqueedo that are driven from their own battery bank. The main source of electrical power is the battery, which is topped up by the engine- driven alternator, although a separate diesel generator is offered as an option. The system operates at a nominal 12 V, which in practice is 13.8 V. Electrical power can be provided in any form needed to support the payloads, with 24 V DC or 110/240 V AC being the most common. Total battery capacity depends on customers’ individual configurations, as additional batteries can be installed to power payloads, and conventional lead-acid and absorbent glass mat batteries and lithium-ion types can be accommodated. The vessel’s own vital systems, including the engine electrics, navigation-related sensors and computers, draw power from their own battery bank, with payloads normally provided with their own separate bank. With a maximum displacement of a little over 2 t, the Mariner can reach speeds of up to 25 knots, depending on the payload installation, although a more representative operational speed would be 4 knots, at which it has an endurance of 200 nautical miles in calm weather over 50 hours of operation. Capable of operating in up to sea state five (although that usually precludes gathering any useful survey data), the vessel can survive in up to sea state seven. The Mariner needs only 80 cm of water in which to operate. Operation, navigation and safety Operated principally as a remotely supervised vessel, the Mariner relies on an autopilot based on a custom- built embedded computer with a low- energy ARM processor. The software is Maritime Robotics’ proprietary autonomy framework developed in-house over the past 15 years, and is written mostly in C++, with C used for low-level drivers. August/September 2021 | Unmanned Systems Technology A Yanmar marine diesel engine drives the water jet through a mechanical coupling in the current Mariner. Hybrid and fully electric options are in the pipeline