Unmanned MW systems: a simple concept that’s challenging to deliver
The “system-of-systems” approach required by next generation, unmanned MW systems must guarantee mission success, often in difficult conditions, time after time. Key to this challenge is the system’s workhorse: the unmanned surface vehicle (USV). The needs are complex and specific, and, while selecting an apparently suitable boat from the market and adding autonomy may appear financially attractive, doing so can ultimately be disastrous.
Complex needs favour dedicated design
The USV must handle a set of unmanned vehicles, which may vary with mission or future developments. Here, flexibility means designing for maximum payload. It must be rapidly deployed too, transportable by air and road. Both directional and positional stability are required for optimum sonar coverage, and secure launch and recovery. Also, the USV will be approaching mines. If they detect its signature and detonate, the result may be the loss of a significant investment. The myriad of detailed needs behind these broad areas points clearly to the need for a dedicated design.
A holistic approach is essential
This complexity is compounded by numerous interactions and trade-offs. Addressing one need in isolation may see another compromised, or simply not met. Maximising payload favours a large boat, but this trades off sea keeping qualities—putting high-value equipment at risk of shocks and damage; a catamaran is highly stable, but its beam-to-length ratio will rule out air transport; and so on. As well as dedicated design, meeting navies’ needs requires holistic thinking—from the conceptual stage on.
Hull form: a major piece of the jigsaw
Getting the hull form right is a key step. A semi-planing hull enables the deck size to be maximised, while still sizing for recovery to a mothership using conventional davits, easy access to an aircraft cabin by ramp, and unescorted travel on roads. It also offers good directional stability—avoiding the side-to-side movement that hamper sonar operations. When combined with the careful placing of elements like bow thrusters, a USV can achieve good positional stability too. This allows it to “hover”, underpinning launch and recovery—and fostering an accurate sonar picture.
Signature control and shock resistance: key to safe and secure operation
But all this counts for little without considering both signatures and shock. Good acoustic design from the conceptual stage is essential, for example, choosing tunnelled shafts and acoustically efficient propellers, rather than the noise-producing water jets used by many USVs. For magnetic signature, materials are the key. Even the magnetic environment in the constructor’s factory has a long-term effect on signature, something that must be carefully analysed. Structural layouts of most off-the-shelf boats would simply not survive in certain operating scenarios. Conversely, selecting panel sizes, internal stiffener and bulkhead locations that are optimised for mine shock resistance will result in a highly rugged boat, more than capable of standing up to the tough environment of MCM operations.
Detailed design: an exercise in the mastery of detail
Having made the essential choices, designers must then optimise the detail. The deck must maximise the space available for payload handling and storage. This means hard thinking about maintenance and careful wheelhouse design if the USV is to be optionally manned. The stern must be as close to the water as possible, requiring careful choice of deck angle and transom height. Finally, but crucially, all on-board equipment needs to be carefully considered from the beginning. Mine obstacle avoidance sonar illustrates the point. Deployed through an opening in the hull, it protects the USV from moored mines, and the risks of retrofitting such critical equipment to an off-the-shelf boat are high.