ABSTRACT

The Unmanned, Untethered, Underwater Vehicle MARTIN was launched by Maridan, Denmark in 1995. MARTIN is being instrumented for bathymetry and inspection of offshore installations (pipelines, sea cable). Sea trials are continuing. UUV are expected to become a feasible supplement to ROVs for many types of offshore surveys. An occasional ship can be used as mother ship since dynamic positioning (DP) is not required for UUV-operations.

MARTIN is currently being operated in UUV-mode with the operator onboard the mother ship. The navigation system make it possible to fly very close to the seabed for pipe tracking. Path control including obstacle avoidance is automated. Path calculations are carried out in a horizontal plane based on input from a high resolution multibeam sonar.

The Autopilot based on an adaptive controller takes care of the low level control of rudders and thrusters. Positioning is carried out by tracking MARTIN from the mother ship. Position data are downloaded to the vehicle for updating of its own positioning system.

INTRODUCTION

The AUV (Autonomous Underwater Vehicle) MARTIN was developed for oceanographic and industrial surveys in shallow water down to 100 metres. The depth rating is currently being upgraded to 600 metres to cover oil industry requirements. The hull and basic power and propulsion systems are based on the prototype vehicle MARIUS1,2,3 developed under the European Community Programme Mast (Marine Science and Technology). Tank tests and sea trials with MARIUS have proved excellent manoeuvrability of the flatfish shaped, low-drag hull4 (Figure 1).

Figure 1 : The two vehicles, MARIUS (photo) and MARTIN, have the same shape (Length 4.5 metres) (available in full paper)

Typical applications include pipeline and cable surveys, bathymetric surveys and surveys in connection with construction of new offshore installations. A modular design f compartments for instruments and navigation system was adopted in MARTIN due to its flexibility in different operating modes. The modular design allows easy installation of specific payload instrumentation. Electronics is housed in several small cylindrical compartments (Diameter Ø200 mm) connected through a CAN network (well known from the automobile industry). A new type non-metallic low-weight GRP-based composite material was used for pressure compartments.

Unmanned Minisub For Offshore Inspection

The low level Path Control and steering are automated. However, Mission Control is taken care of by an operator onboard the mother ship. The operator controls MARTIN by transmitting high level commands.

The communication link is based on acoustic communication between MARTIN and the mother ship. Today the maximum distance for acoustic communication in a horizontal channel is 2 km, but future UUV-surveys may be carried out at a distance of 30km or more form the operator. This seems possible as acoustic network communication systems are being improved.

For sea trials in very shallow water, a floating antenna enables transmission of video and sonar images to the operator via radio signals.

The four operation modes commonly referred to for unmanned systems are ROV-mode Tether mode, UUV-mode and AUV-mode (figure 2)

Figure 2 Different modes of operation from ROV to AUV with increasing autonomy (available in full paper)

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