Autonomous boat defies the waves

A boat whose bulk is underwater – with only a narrow element jutting above the surface – is largely unaffected by the swell of the sea. The vehicle was conceived as a ‘wave piercing’ craft to provide a stable platform for underwater surveying. It can easily be made small and autonomous, and run at a fraction of the cost of a conventional work boat – and an even smaller fraction of an unmanned underwater vehicle. It has been proven as a working prototype and is about to be used commercially as a survey tool. If ever built large enough, it could form the basis of ferry craft that could transport passengers with very little risk of inducing sea sickness. The craft, developed by a team at Autonomous Surface Vehicles (ASV) in Chichester, moves about under robotic control – either pre-programmed or remote – and undertakes surveying and observing tasks largely unaffected by waves. Technical director Daniel Hook, told Eureka during the recent Unmanned Underwater Vehicle Showcase: “We are looking at boat replacement. It is powered by the same type of diesel engine, uses the same type of sonar to do surveying and GPS for navigation, but comes at a fraction of the cost. It is also exceptionally stable.” The prototype vehicle, recently seen on the dockside at Southampton, has a weighted keel, a main body constructed like a torpedo, and a tall fin – on top of which sits the engine compartment and GPS antenna. It is this configuration that delivers the stability. As it passes through a wave, the change in displacement caused by rise of the wave profile relative to the volume of the fin is very small, compared with the overall displacement of the vehicle. This means that the increase in upthrust is insufficient to make the vehicle rise significantly within the time it takes to pass through the wave. The prototype has a pair of hydroplanes for active control, but Hook says they proved to be unnecessary, and will be removed from future designs. Torpedo appearance Research into the feasibility of the idea began with the aid of a Link Award in 1998, followed by a DTI Smart Award four years ago, and a joint development programme with the University of Southampton. This led to construction of a 2m demonstrator followed by the current 6m version seen at the show. Despite its torpedo-like appearance, it is simply constructed – from foam, aluminium alloys and fibreglass – with a fairly straightforward mechanical transmission from the engine to the propeller. Managing director Stephen Phillips insists it is around a hundred times cheaper to run than a conventional workboat, and very robust: “If you were to take a hammer to it you wouldn’t make any impression,” It is also cheaper than Autonomous Underwater Vehicles (AUVs) because it does not have to withstand depth pressures, or be equipped with a dead reckoning inertial navigation system. In addition, should something go wrong, it is much easier to find than an AUV. The company has recently completed the design of a 5.5m semi-submersible version for C&C Technologies in the USA. Construction has recently begun with demonstration trials planned for 2007. The vehicle will be fitted with a number of sonars and is intended for commercial hydrographic survey activities: charts of rarely used waters are often found to be inaccurate, so harbours, rivers and estuaries must be constantly re-surveyed to discover accumulations of material that could damage ships and large boats. Wrecks and other underwater objects also have to be accurately located and marked if necessary. The new vehicle operates at a speed of 8 knots with a maximum speed of 10 knots and an endurance of 48 hours in rough sea conditions. Unlike the current 6m vehicle, the new one will have its engine in the body. “This makes it much easier to launch and recover,” said Hook. The original idea of having the engine on top of the fin was to reduce noise that might interfere with sensitive underwater measurements, such as the assessment of fish stocks. There has been lots of interest in using the design for other applications. Because it provides a stable camera platform, it could be used for marine surveillance, or to locate illegally used vessels – since it is cheaper and much less obvious than a coastguard cutter. While its above-surface superstructure makes it unsuitable for undertaking sneak attacks, it can be used as a stable platform for mounting mine-hunting sonars. The vehicle is also suitable for fishery and marine research and environmental monitoring. Daniel Hook said of its prospects: “Over the last few years, unmanned vehicles have taken off because of advances in technology and their low running costs. We look on ourselves as a platform supplier. What we have is a sea truck on which customers can mount whatever payloads they please.” Autonomous Surface Vehicles Pointers * The basic configuration is hardly affected by waves, so that it works as a stable sonar surveying or video surveillance platform * As a surface vessel, it is much cheaper to construct than an AUV; being autonomous and small, it is much cheaper to run than a work boat * A commercial version is being built and will begin trials in 2007