The Stirling Clyde back then pumping to a Brent Platform, probably using its DP1 system. Photo Derek Mackay.

This is an article written for a marine magazine back at the turn of the century. It contains a bit of history, and readers will see that the DP1 systems which were in place then have been replaced, in many cases by DPII systems. However the basic principles discussed can be applied today – the capability of the deck officers to actually drive the ship, rather than letting the computers do it.

The latest spate of supply vessel deliveries seems to have widened the gulf between the activities of platform ships and anchor-handlers in the North Sea. The cost of the latter due to the larger engine size and the winch installation has meant that they are generally less economic as cargo carriers and are often engaged in other tasks which relate more to the ability to pull things, than the ability to carry things.

In addition, the tendency for oil companies to farm out their marine activities to logistics providers has emphasised the requirement for large platform ships, which fulfil a schedule between several fields or platforms, and take in any mobile units which the operator may have contracted. This is in contrast to the tendency, in the early eighties, for operators to use a mix of anchor-handlers and platform ships, the former carrying cargo routinely and then taking on the task of rig moving when required. Of course, in places like the middle east this process is still followed, the division of services most likely being between the ships servicing platforms and those servicing mobile units. All the vessels serving the mobiles units will have winches, although to call them anchor-handlers might conjure up images somewhat removed from the actuality. Ageing UT704s are monsters in the world of Middle Eastern jack-up moving.

However, in the North Sea the division of the tasks, and the tendency for operators or logistics suppliers to hire anchor-handlers off the spot market has made the provision of cargo carriers a specialised activity. This in turn has caused the owners and charterers to focus on the specifics of the operation. The ships have to be able to carry large amounts of cargo on deck, a selection of commodities underdeck and have high pumping speeds for all bulk cargo. They must be able to transit between the base port and the fields at a reasonable speed without consuming an excessive amount of fuel. The Stirling Shipping VS483s for instance claim a service speed of 12 knots consuming 6 tonnes of fuel per day.

When in the field they are required to be capable of manoeuvring within the radius of the offshore cranes, and then remaining in position for hours at a time while quantities of deck cargo are discharged at loaded and bulk and liquids are pumps up. This used to be known as "snatching" but now that nobody ever ties up to an installation in the North Sea the term has fallen into disuse. The first oil company to adopt snatching as the means of maintaining the position of the ships was Britoil, operators of the Thistle platform in 1976. Not because they meant to, but because they forgot to provide any means of attaching the ropes to the jacket. Others followed suit and it quickly became apparent that if one did not tie up then it would be possible to work ships sideways on, and then it would be possible to use what were then pipe carriers.

The shipmasters at the time adapted their techniques and discovered that being sideways on usually made it easier to judge the distance between the ship and the rig - the most important parameter in this equation, and they were soon being assisted in their task by the joystick which offered single stick control of engines rudders and thrusters. Of course there were old seadogs who poured scorn on the use of such new fangled devices, claiming that the joystick lacked the sensitivity required for some tasks, and that its reaction time was too slow to react to sea and swell.

The one thing which the joystick offered was a guaranteed heading which once more made reference to the rig easier, and what-ever the misgivings of the traditionalists, guaranteed it adoption into general use.

In the early eighties there were rumours that some ships were fitted with DP - dynamic positioning, and that the master, once he had carried out the approach, just had to sit back and keep a general eye on things. At least part of the rumour was true. Edda Supply ships had fitted an AEG Television Tracker system to its advanced platform ships the Edda Fram and the Edda Fjord both of which were brought into service in 1982. The system worked using a television camera mounted above the bridge, which took two contrasting images of the installation and then interacted with the ship to keep the images in position.

The ships used the system without telling the charterers and in general the impression was maintained that the masters were both tireless and extremely competent. Those who remember it consider that it was, at least in part, successful because the masters were required to be constantly alert, in case a seagull happened to fly in front of the camera, or a particularly slow moving crane lift caused the ship to start following it. The impression was that the DP system operated like a trainee losing concentration, requiring the master to be constantly looking over its shoulder with fingers poised to take over.

From this some-what faltering start the search for a suitable referencing system continued and with the arrival of Measurement Devices Ltd "Fanbeam" it may have been found. Numerous fanbeams are now installed on ships built in the last few years and also some have been retrofitted to older vessels, replacing less reliable systems. The latest incarnation of the Edda Fram for instance, is fitted with a Fanbeam. However, despite the improvements resulting from the use of laser technology, systems using a single reference source are still not absolutely reliable.

Even the laser systems have failings. They are not keen on cement dust or heavy rain and tend to become less trustworthy as the movement of the ship increases. Such failings can lead to accidents, particularly if the bridge team have not been monitoring the strength of the signal or the use of power.

 Collisions, like any other accidents, require a combination of a number of circumstances and the nightmare scenario is as follows. A large platform ship is working to windward in increasingly adverse weather but the bridge team on the ship are unaware of the increasing difficulty the vessel is having in maintaining its position. Finally the rolling of the ship degrades the signal to a point that the DP computer works on its stored information while waiting for a new signal. It is only when the new signal fails to be established that the vessel begins to move out of position. The master, who has not been observing the trends, grabs for the joystick selects it and moves it in a direction to take the ship away from the structure. Of course under pressure it would be easy to select the wrong mode, or else to allow the joystick to select its own primary task, which might well be to restore the heading before moving the ship away. In any of these cases the ship could well end up landing heavily alongside the platform with resulting damage to both. As has already been mentioned, these platform ships are getting larger and some platforms are quite small.

In addition to the unease created by the lack of total reliability of DP1 single reference DP systems, which in the case of BP Amoco has resulted in their use being banned altogether, there is also an awareness that the increasing reliance on both the DP systems and joysticks may be resulting in a lack of competence in basic ship handling.

It is possible that deck officers are entering the industry and being assigned to vessels which are provided with extremely sophisticated joystick and DP systems, and that the masters routinely use such systems for all purposes, including berthing and unberthing. The trainee shiphandlers may therefore never actually work the ship "on the sticks". This expression means using the engine rudder and thruster controls individually to achieve the movement or non-movement of the ship. Perhaps the expression is even falling from use like "snatching".

The answer which is proffered, if such questions are raised, is that there are nautical training establishments with simulators, which are used to train bridge personnel. If one asks what is wrong with training them using the actual ship, it then usually transpires that the simulators are used to enact system failures and consequent emergency actions, and this seems to solve one of the problems resulting from DP system failure.  However, it must surely be necessary for all ship-handlers to be aware of the precise forces which are being engaged by the DP system or the joystick to maintain the ship in position, and it would seem that the only way of gaining this awareness would be to learn to drive the ship "on the sticks". Such training might be part of a structured programme which would take in simulator training as well.

Curiously, it can be seen that some bridge designers do not even expect the person at the controls to be doing anything other than operating the joystick. On some ships the throttles, rudder controls and thruster controls are suficiently distant from each other that the driver cannot operate them all without constantly moving around. 

MDL have developed a 7.5KHz repetition rate laser head which they claim improves performance in poor weather, and doubtless in cement dust laden atmospheres, and it may be that  in time an economical DP2 system will be developed which will solve more of the reliability problems, but this still leaves the need for competence. It is generally expected by charterers that supply ships will come with masters, and in some case other deck officers capable of driving them. This is not an unreasonable expectation, which should be fulfilled regardless of the positioning equipment on board. 

 
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