Unmanned Systems Technology 006 | ECA Inspector Mk2 USV | Antenna systems | Northwest UAV NW-44 | Unmanned ground vehicles | Navigation systems | Lunar X challenge

The conflicting speed and stability requirements demanded an innovative hull design, as survey ships are usually dedicated to their sedate role and not expected to perform target tracking tasks at high speeds in a homeland security application as well. “The design of the hull is a very big compromise,” Clavier says, although he would not be drawn further on the details of that. However, one area of compromise in 25 solutions to good steering control and very accurate path tracking at speed in high sea states include combining a unique and proprietary hull design with water-jet propulsion; ECA determined that water jets provide finer directional control at critical speeds. This chimes with the acknowledged advantages of well-designed water jets, which include elimination of any deadband – a lack of steering response immediately adjacent to the dead- ahead position – along with the ability for infinite adjustment of the split-duct thrust reverser between full ahead and full astern so that the vessel can be held against a current or crept ahead or astern, plus plenty of steering authority. Like the hulls of most small powerboats, the Inspector Mk2 functions as a displacement hull at low speeds, at which its weight is supported by its buoyancy, and as a planing hull at high speeds when hydrodynamic lift dominates. For ECA, it was critical to ensure that the boat would always climb onto the plane at a speed much higher than the patrol speed to ensure that any instability around the transitional drag- increasing ‘hump’ between buoyant running and planing cannot degrade the performance of the underwater sensor during surveys. hull design for boats that must operate over a wide speed range is in deadrise, which is the sharpness of the hull’s vee- shape or, more technically, the angle the bottom makes with the horizontal when seen from in front or behind, and which is a strong determinant of the speed at which a planing boat runs most efficiently. Flat-bottomed boats – with little or no deadrise – are more efficient in smooth water but don’t handle rough water very well, while the opposite applies to deep-vee hulls – with large deadrise angles – which cut through waves well but produce more drag. This is a sound reason for customers who want their USV system to perform one role only to select their own boat, perhaps from another manufacturer, and have ECA integrate its sensors and so on into it, Clavier says. Unlike many boats of this size, the Inspector Mk2’s hull is made of aluminium rather than a composite of fibre-reinforced plastics. Clavier explains that the prototype was built from aluminium because at the beginning of the project the team wanted to be able to make any changes to the hull easily. For example, they considered including a well to accommodate a through-hull sensor. Recent developments in new alloys, and fabrication techniques including cutting and welding, along with inherent corrosion resistance and impact toughness – particularly important in rivers where semi-submerged logs can be hazardous – and growing familiarity with drawbacks such as delamination, blistering and structural fatigue of composites, have increased the popularity of aluminium as a hull material. The riverine environment is important to some of ECA’s customers, Clavier says, “So for all our applications the best compromise was aluminium because we thought that for river applications it would be better than fibre.” Aluminium also makes it easier to include strengthening members to support the removable top of the cabin roof, which is important to Unmanned Systems Technology | February/March 2016 Unlike many boats of this size, the Inspector Mk2’s hull is made of aluminium rather than fibre- reinforced plastic Optionally manned, the vessel can be driven conventionally or autonomously with the onboard crew of up to six acting in supervisory mode