ABSTRACT

Subsea intervention tasks are becoming more complex at the same time as the consequences of operational failure have become more critical, and emphasis on cost control continues to mount.

Our present generation of work vehicles is being pushed to the very limit of its performance, so that almost without realizing we have increased the risk of operational failure, just when we should all be attempting to achieve the opposite.

Solutions to this potential problem are discussed including increased technical awareness among users and suppliers of underwater systems, a new generation of ROVs, and new ways of configuring existing vehicles.

INTRODUCTION

Work class ROVs have served the industry well over the last decade or so. One measure of their success is the increasing complexity and criticality of the tasks that they are being required to accomplish in harsher environmental conditions.

But, as with any type of machine there are limits to how much performance can be coaxed from these systems without compromising their ability to complete tasks safety, reliably and economically.

As we edge nearer to the performance limits of the ROVs in our existing fleets, operating crews are forced to work with less spare capacity that can be called upon when unforeseen circumstances arise.

Unless this trend is acknowledged and acted upon, we might well see a reverse in the continuing trends of flexibility, reliability and dependability that have been so hard won over the years.

History

Subsea Offshore has nearly twenty years experience of operations with work class ROVs. Ignoring some of the early vehicles (which are probably best forgotten), the arrival of Ametek's Scorpio vehicle in the late seventies set new standards of reliability for the industry and remains a much admired and copied vehicle.

The original Scorpios weighed about a tone and had a 15 horse power electro-hydraulic power pack for propulsion and the operation of auxiliary equipment such as a manipulator, cutters and so on. Available power was quickly increased to 25 and then 40 horse power.

After numerous refits, over the years, our remaining Scorpios typically tip the scales at about one and a half tones, are fitted with a 50 or 75 hp power pack and have been modified in many details to increase their operational flexibility and effectiveness.

This progression typifies the development trends in work class ROVs over the last decade or so

  • More power available for propulsion and other, work related, tasks

  • More data and control capability. This is primarily related to the more complex tasks now being required from the systems, because the vehicle control overhead on the data transmission electronics, is almost the same now as it was in those earlier days (i.e control of movement in four to six degrees of freedom, depth, heading indication and so on)

  • Increased size and weight due to the addition of more powerful propulsion systems, enhanced task capability and the need for larger payload capacity

These general purpose vehicles have been utilised for a great variety of tasks over the years.

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