The paper describes the development and use of novel unmanned data gathering platform well suited to offshore surveys. The technique is that of unmanned wave-piercing vehicles (UWVs). These vehicles combine many of the advantages of unmanned surface vehicles(USVs) and unmanned underwater vehicles (UUVs). They can have the endurance, economy and speed of the former, combined with the stability of the latter to give a mobile, stable instrumentation platform for sensors in significant sea states. The concept has evolved since 1998. Research has culminated in development for clients and private venture and an order to design a vehicle specifically for offshore survey.
Unmanned systems have well known and proven applications on land, at sea, in the air and in space. They generally provide cost effective alternatives to manned systems engaged in activities involving significant danger, which are tedious or repetitive, or where the optimisation of unmanned systems can provide significant commercial or technical advantage (for example by miniaturisation).
At sea, unmanned craft have taken the form of surface or underwater vehicles, or hybrids of the two, underwater vehicles clearly have the advantage of being able to dive to depth to give excellent image resolution but suffer from lack of real endurance and speed via a power umbilical. Likewise, the transmission of data to and from the underwater vehicle is also very limited unless via a data transmission umbilical, thus real-time communication and position fixing are particularly restricted.
Unmanned surface craft can operate with diesel power to give markedly better operational availability and can use normal radio and satellite data communications for real-time data transmission and position fixing. Traditionally, however, small surface vehicles have been limited by their seagoing ability.
By the use of unmanned wave-piercing craft, this seagoing limitation has been significantly reduced and, in addition, their use in combination with fully submerged daughter vehicles enables data from the seabed to be transmitted in near real time. This technology permits small wave-piercing vehicles to deploy sensors for gathering data from below or above the sea at significant distances away from a ship, a platform or from shore, positioned by GPS and communicating by ratio. It is because they are inherently surface vehicles and thus float at operating depth that they remain stable at slow to zero speeds, and it is this feature that enables them to deploy sensors to depth either from winches or from daughter tethered remotely operated vehicles (ROVs) pr untethered UUVs.
Autonomous Surface Vehicles (ASV) Ltd has researched this technology and developed a number of such craft. Its concept originated in 1995 discussions concerning the high peripheral costs associated with data gathering. In 1998 development started with small research vehicles to explore new ideas (see Figure 1), progressing to a large, 6m, diesel-powered prototype which proved the wave-piercing technology at full scale. This has developed into the ASV 6000 SASS Q, often abbreviated to SASS, standing for survey autonomous semi-submersible. ASV is now designing and building commercial unmanned wave-piercing vehicles for survey and visual surveillance. Plans for further research and development are well advanced.
