Unmanned Systems Technology 009 | Ocean Aero Submaran S10 | Simulation and testing | Farnborough report | 3W-110xi b2 TS HFE FI | USVs | Data storage | Eurosatory/UGS 2016 report

24 Dossier | Ocean Aero Submaran S10 more, with the ability to submerge to 10 m and the option of an electric thruster for underwater propulsion. Glass-fibre reinforced plastic (GRP) is the primary hull material with, for example, G10 glass epoxy laminate used for the internal bulkheads. Childress emphasises the S10’s lightness, quoting its complete dry weight as 127 kg. Measuring 4.14 m in length and 2.45 m high with the wing sail up, it has a keel to balance the heeling force from the pressure of the wind, its moment arm terminated by a bulb weighted with lead. Made from machined and anodised aluminium, the keel is bored down the centre to accept cabling for sensors that can be installed in the keel bulb. The hull has a slot along the deck in which the wing sail sits after folding down before the boat slips under water. Twin angled ruddervators – which act as rudders on the surface, and elevators when submerged – pivot on the rear of the hull. Fully floodable, the hull also contains four additional ballast tanks (for stability and trim control), lithium batteries, control electronics and payload bays with a total capacity of 23 kg. The solar panels are laminated into the deck. The solar panels and batteries provide a little over a kilowatt of power, with the panels able to recharge the battery system fully with about six hours of sunlight, giving it an endurance measured in months. “If it gets about 18 hours of sunlight a week, that is typically enough to keep it going continuously,” Childress says. So far, S10s have undertaken voyages lasting a week to 10 days, but the company is planning much longer trips. “The boats have performed very well with only minor glitches with stuff like sensors and software,” he adds. Sensing and comms The baseline set of sensors includes an anemometer on the masthead to measure wind speed and direction. An inertial measurement unit and GPS receiver measure wave height and frequency in addition to their navigation functions, while other sensors measure air temperature, water temperature, speed over water and speed over the sea bed. These all provide data that the S10 needs for navigation and control. For comms, the S10 relies on an Iridium satcom system for global coverage, and cellular and wi-fi systems for higher data rates over shorter ranges. It also features an automatic identification system with listen and selective broadcast modes, and Novatech iBCN Iridium beacons from MetOcean that enable it to be tracked around the globe. Initial funding from investors including Teledyne, which currently holds a 37% stake, enabled Childress and Ott to build and test the first prototypes, and they had been joined by engineer Vance McClure, “a brilliant guy who did most of the design work on the early vessel” according to Childress. By early 2013, the prototypes were working well and the submersible sailing boat concept was gaining traction with potential customers including the US Navy, giving Childress and Ott the confidence to set up Ocean Aero in December of that year. Four months later they invited retired US Navy captain Eric Patten to join the company as CEO. Sinking a sail boat Most sailing vessels must be as buoyant as possible for obvious reasons and, equally obviously, sinking one involves filling it with water. Beyond the obvious, however, fine control was a challenge, one that the team addressed with a dedicated prototype. “It took us a long time to develop the buoyancy changing system so that once the boat was flooded with water, we could then control the additional volume of water required to take it on down,” Childress says. “So we’ve developed a pretty unique buoyancy system that uses a combination of water and compressed air balanced against each other. “We built a whole boat that was nothing but the hull with the ballast system in it that we called the Mule. And it spent its life in Teledyne’s test tank in San Diego going up and down trying to work out all the subtle things.” One example is the sensitivity of buoyancy control to bubbles, which must be kept to a minimum in the ballast water. To begin the submergence process, the ballast trim tanks are pumped full to what Ocean Aero terms the “buoyancy August/September 2016 | Unmanned Systems Technology The S10 rigged for surface running with wing sail folding, angle setting and flap adjusting mechanism visible at the base