In February 2005 ILV Granuaile was chartered by Marathon Oil, owners of the Kinsale Gas Field, to assist in a pipeline survey. For three days Marathon engineers staying on board used the latest remote operated vehicle (ROV) technology to inspect numerous pipelines and manifolds in the gas field.
Gas production companies carry out such surveys regularly to ensure that there is no loss of either gas or hydraulic fluid through the pipework. The pipelines are inspected by means of an ROV, which is a mini-submarine and which come in many sizes. Granuaile herself carries a small ROV that is used for various underwater inspection tasks. Marathon's ROV was significantly bigger.

An ROV basically consists of one or more underwater cameras mounted in a box-like frame with several spotlights and three small propellers. Two propellers are used for forward or reverse manoeuvring and the third, mounted on the top, for diving or surfacing. A trailing cable to the ship allows an operator to drive the sub and control the lights and cameras. A transponder on the ROV communicates with another transponder protruding below the ship's hull through the moon pool. This allows the operator to know precisely where the vehicle is in relation to the ship. This is important in order to keep the sub clear of the ship's propellers and also to guide the ship to follow the sub as it tracks along the seabed.

Most people nowadays are familiar, even if unknowingly, with ROVs: one was used to film the opening scenes of the movie Titanic, where shots were taken of the actual wreck at the bottom of the Atlantic Ocean.

The whole venture nearly ended in failure before it started, when last minute technical problems with the ROV before it left its home in Skibbereen appeared irreparable. The ship, meanwhile, waited patiently in Cobh. However, after hours of checks the problem was found and repaired, and at 0100 hours on 13 September the people and equipment were embarked and the ship sailed at once for the gas field. Early next morning, the vessel was on site and sitting over the first area of inspection.

After assembling all the equipment, including the mandatory bunch of computers, and then a final series of checks, the ROV was ready for launch. This in itself was a complicated operation. The ROV is an expensive and delicate piece of apparatus and great care must be taken to avoid damage while placing it in the water. For this purpose, a long slip line was used, running high above to one hook of the ship's crane and down to an eye on top of the ROV. When slipped, the ROV was free to manoeuvre. The cable from the ROV ran back through a block on the crane's second hook to a cable drum and ultimately to a junction box connected to the operating system.

The ship's buoy workshop was commandeered by the Marathon engineers as the ROV operations centre and soon became very congested with both equipment and people. Our Electrical Technical Officer connected up the central ROV monitor to the ship's CCTV system so that a live feed of the underwater action was available throughout the ship, including the bridge.

As the ROV dived through the water little could be seen on the display monitor except for a wall of fine bubbles. Only when it approached the seabed did the picture become clear. At 93 metres deep it quickly came into view with startling clarity. Flat, sandy, and featureless, it looked almost like a desert with water on it!
The plan was to track north-south across the seabed until the pipeline, which ran east-west, was encountered, then to turn and follow it west to a large manifold called a tree-a sort of pipeline junction where the gas emerges from the seabed and has numerous valves and connections, rising some 5 metres above the seabed. This tree, known to the engineers as Well 48/25-E, require regular survey as the valves are operated by hydraulic fluid in separate pipes, in the same way as the brakes of a motor car.

I had always thought that the pipeline system in a gas field consisted merely of one line from each well running to the nearest platform; then a line from there to the main platform, where they combined into the main gas line that ran to shore. How naïve I was. The seabed in a gas field system is a virtual spaghetti junction of pipelines-gas lines, hydraulic lines, electrical lines, and whatever you're having yourself!

In our case no pipeline appeared but after some consideration and a little repositioning, sure enough, it loomed into view. Not an actual pipe, but a large mound of rocks, called simply a rock dump, that covered it in a sort of armour. The ROV turned and scooted along the line with the ship slowly following on the surface. Following the line was a bit like trying to follow a road from a helicopter. There were no signposts so you continually checked the map for junctions that could tell you where you were. It turned out we were over the right road and eventually, after only one hour's searching, the tree appeared out of the gloom. It is a large steel structure that, to the untrained eye, is an incomprehensible maze of pipes, valves and connections. The engineers smiled happily, talking among themselves in their own incomprehensible jargon.

The engineers had indications of loss of pressure but there was no sign of anything amiss. The rov circled several times but the only thing of interest (to non-experts) was the variety of marine life that appeared. In contrast to the barren sea earlier, these trees act as a sort of assembly point for many types of fish and crustaceans much like a coral reef. Several types of crab, shrimp, and various silver-coloured fish moved eerily through the manifold.

It was decided to get the Kinsale Alpha platform, some three miles away, to pump along the hydraulic line some fluid to which a green dye had been added. The effect was instantaneous. A green cloud could be seen coming from a large box manifold beside the tree. Success! The whole thing was recorded on video for analysis so that a repair programme could be devised. Deep-sea divers, working from a specialised dive-support vessel, would carry out these repairs at a later date.

After detailed examination of the whole area, the ROV was recovered. This was almost an exact reversal of the launch operation except that this time the eye on top of the sub had to be hooked using a long pole with a karabiner clip attached. This was the most delicate part of the operation, as it had to be done quickly to prevent the ROV from bashing on the ship's side. Our chief hooker, Harry, soon became expert at this tricky manoeuvre! After that, the transponder had to be removed from the moon pool before the ship could move on.
In the next 2½ days, more pipelines, trees, and pipe line end manifolds (plems) were visited and studied carefully, and each time the operation was a success. With the exception of the second evening when weather deterioration caused a temporary suspension of operations, the conditions were very good for the season with sunshine and calm seas. After three days and six ROV sorties the operation was successfully concluded and the ship sailed again for Cobh where men and equipment were disembarked.

For the crew of Granuaile this was a new experience and very different from our usual activities. Of course, all experience is valuable and next time we will all be nodding sagely when we hear mention of manifolds, trees, plems, skids, mattresses, rock dumps, and other arcane terminology.
Next day it was back to the normal run of operational dut

ies and buoywork on the south-east coast.
Ah well….

© R. Mullins, 2005