Remotely Operated Vehicles (ROVs) presently perform a wide range of tasks in a variety of underwater scenarios ranging from research, through commercial oil support and on to military applications. A number of technology leaps, during the period from the mid-70s to the present day, have meant their greater operation has also greatly improved through this period, and operational availability in wider weather windows has added to their attractiveness as an alternative to divers. Deeper waters have also led thoughts along the path of necessity-if commercial operations go deeper, then ROVs may become even more attractive.

So what is expected of future ROVs? The simple answer at this moment in time is ‘autonomy’, but to make the present-day ROV autonomous may not be a short-term task--or will it?

BACKGROUND

There exists a large number of ROV users who would like to operate their present vehicles in a more economic fashion and see technological advances as a means of achieving this as they venture into the deeper, and deepest waters. Figure 1 shows a typical ROV operational configuration of equipment. This system can be found in similar forms in most kinds of ROV application today. Figure 2 shows the ‘ideal’ autonomous ROV operational configuration and the savings that could potentially be achieved are immediately apparent. Assuming that an autonomous ROV contained its own power supply, in-built control and navigation systems as well as full data-logging capability, then the equipment savings could be summarized as:

  • No large generator/ships supply requirement.

  • No umbilical.

  • No umbilical winch/associated power pack.

  • No control cabin/power distribution system.

  • Minimum control console requirement. Acoustic intervention control possibly, with some video feedback.

  • No subsea Tether Management System (typical in deep water applications).

Fig. 1 Ship/rig.(available in full paper)

Fig. 2 Small ship or rig.(available in full paper)

At first glance, the capital equipment costs could be slashed, and with the possibility of adding reduced ship costings into the equation then the autonomous ROV looks very attractive. To achieve this, what would it mean in terms of technology?

PRESENT-DAY ROVS

In almost all of today's ROVs, the umbilical or tether is identified as the single most restrictive item. If a ROV needs more power for a task then the umbilical grows, hydrodynamic drag increases and more power is required. Umbilicals also tend to get snagged from time to time or damaged by other means. In some ways umbilicals may be considered as operational consumables, but very expensive consumables. The handling equipment required for an umbilical system adds significantly to initial capital cost. Thus, the ‘umbilical must go’ school of thought has been a great supporter of the autonomous ROV of the future.

However, the functions that the umbilical provide have to be provided in the non-umbilical system.

These include.

  • Power supplies for hydraulic/electric systems including propulsion, power tools etc.

  • Power supplies for instruments (electronics, video, navigation equipment etc.).

  • Data link/telemetry lines (fibre optic, copper twisted pairs).

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