ABSTRACT

The development of Autonomous Underwater Vehicles (AUV's) has progressed considerably during the last years The capability of existing prototypes indicates that free swimming AUV's in few years probably will become commonly used for underwater surveys, just as Remotely Operated Vehicles (ROV's) and Remotely Operated Towed Vehicles (ROTV's) are today

A full scale cable and pipeline inspection survey with the prototype vehicle MARTIN 100 (Water Depth 100 metres) is scheduled for demo in 1998 The survey will be carried out from a mother ship following the AUV The AUV should be within a radius of 2 km from the mother ship for upload transmission of selected survey data and download transmission of high level survey commands

A new design initiative for AUV's is under development by Maridan It includes the addition of an AIP (Air Independent Propulsion) energy module based on the Stirling engine A new prototype MARTIN 2000 (Water Depth 2000 metres) is being constructed with a range of 500 km at a speed of 2 5 m/s (5 knots), submerged survey time 55 hours

INTRODUCTION

Free swimming Autonomous Underwater Vehicles (AUV's) are being developed at several universities and oceanographic organisations in U S A, Europe and Japan A few companies (including Maridan, Denmark) are now prepared to start marketing of AUV's for offshore Surveys

Figure 1 Autonomous underwater vehicle MARTIN 100 (Available in full paper)

Surveys that can be performed by AUV's include

  • External Pipeline and cable inspection (free span, anchor marks)

  • Route surveys, gravel dump surveys

  • Bathymetry surveys

  • Oceanographic surveys, environmental monitoring (oxygen depletion)

  • Search for dropped objects

  • Special surveys, hazardous or less accessible areas (mine hunting, chemicals, under-ice)

The advantage of using Awls instead of Divers, ROV's or ROTV's are that no physical connection to the mother ship is required This makes it possible to use an AUV on a remote location of up to a few kilometre from the mother ship The mother ship can therefore perform another job at the same, if required Another advantage is that the AUV can follow a straight line very close without being disturbed by forces from the cable This is of interest when performing synthetic aperture sonar imaging

The drawback by dropping the tether is the limited data transmission rate This means that video cannot be transmitted in real time Furthermore, the amount of energy onboard the vehicle is limited Therefore AUV's will not be able to replace ROV's on jobs that require manipulation or other tasks where on-line video is required

Sea Tests

During the last year, some 25 shallow water sea trials were carried out with the AUV prototype MARTIN 100 (Figure 1) from Maridan's base at the National Laboratory Riso(Roskilde, Denmark) The principal purpose of the trials was to test the navigation system MARTIN was controlled from shore using the radio communication mode with the vehicle near the surface and the antenna mast above the water (Figure 1) The steering control loops are closed onboard the vehicle using autopilots for maintaining heading, speed, altitude or depth

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