Passionate About… Dynamic Positioning

22 July 2008 (Last Updated July 22nd, 2008 18:30)

IMCA chief executive Hugh Williams continues his look at topics that raise passions among offshore specialists.

Passionate About… Dynamic Positioning

This month I am turning my column over to Ian Giddings, technical adviser at IMCA, who joined in December 2006 from the Nautical Institute, the professional body for qualified mariners, where he worked as director of education and training.

IAN’S CAREER

Ian started his career at sea, serving for 14 years aboard a variety of vessel types and gaining his certificate of competency as a master mariner before coming ashore to work at Aberdeen College in Scotland within a team delivering courses to the maritime and offshore industry.

“I'll never forget the first time I watched a shuttle tanker inching towards an FPSO”

He helped develop the college's courses, including the installation of various simulators, for dynamic positioning, semi-submersible stability and self-elevating platform operations for the worldwide industry.

During that time he had the opportunity to gain experience as a dynamic position (DP) operator onboard a semi-submersible accommodation vessel and as a marine surveyor and consultant.

As a requirement of his work at the college he gained a further education teaching qualification.

Here Ian explains why people can become passionate about dynamic positioning:

JUST THE JOB

If a career in the offshore industry is known for anything, it's for the almost endless variety of interest and challenges it can provide.

Dynamic positioning (DP) is just one of the many specialist areas available to master mariners, deck officers, engineers and technicians – and the science of accurately controlling a vessel's position and heading turns out to involve a surprising assortment of skills, techniques and technologies.

DP has a critical part to play at each stage in the exploration for – and production of – oil and gas, as well as in marine construction, diving, hydrographic surveying, wreck investigation, underwater recovery, and site survey, inspection and maintenance.

In all these situations, the role of DP is to control automatically the vessel's surge, sway and yaw as wind, wave and current attempt to interfere with its intended position or track.

It achieves this through a combination of computing hardware and software, signals from transponders and gyrocompasses, and thruster controls, all pulled together at a central control console where the DP operator inputs the desired parameters.

Throw in lasers, global positioning systems, Ethernet, local area network (LAN) connections, transducers and hydroacoustic devices and DP can be seen to offer a tantalising array of technologies, all of which need to work in harmony to achieve the desired result.

FAST EVOLUTION

One of the things that always amazes me about dynamic positioning is just how far, and how fast, the technology has evolved since the first DP-equipped vessel – aptly named The Eureka – demonstrated her decidedly basic analogue control system in 1961.

Nowadays there are more than 1,000 DP-equipped vessels supporting an ever-increasing range of essential offshore activities.

Some are designed specifically for supporting divers; others have wider multirole functions, including diver support.

Life support is obviously the primary task for these diving vessels, and that includes ensuring that there is always a safe distance between the diver's umbilical and the vessel's thrusters and propellers.

As working depths increase beyond the 50m mark, DP vessels become involved in supporting saturation diving, where the divers live in and operate from a hyperbaric chamber, which becomes their home for up to 28 days at a time.

POWERS COMBINED

It's when you combine dynamic positioning with another offshore technological passion of mine, the remotely operated vehicle (ROV), that life starts to get even more interesting.

As with DP, the technology involved in these mini un-manned submarines is becoming increasingly sophisticated, which in turn is leading to wider, and many would say more demanding, applications.

ROVs are used either to observe what's going on beneath the sea during drilling for oil and gas, for carrying out an increasing number of the construction tasks previously handled by divers, for survey and inspection services prior to installation, or to monitor the condition of the installed infrastructure.

The fact that ROVs can operate at far greater depths than divers prompts a marked increase in their use as the search for new hydrocarbon reserves moves into deeper waters.

There's an essential partnership here between the ROV and the DP-equipped support vessel, where engineering decisions centre around the method of deployment and the need to maintain a safe operating distance from any other nearby vessels, drilling rigs or platforms.

"DP enables the sections of pipe to be welded, tested and coated on board."

Among the most interesting applications for DP are the accurate placing and tracking of seabed tractors and trenchers used during the laying and burying of cables and pipelines.

(This is where tracked crawlers are lowered to the seabed and driven along the line of the cable or pipe while the vessel is held accurately above by DP.)

DP enables the sections of pipe to be welded, tested and coated on board, with the barge periodically moving by the exact distance of each joint length.

Dynamic positioning also comes into play in controlling the placing (dumping) of rock on the seabed, either to protect pipelines or combat erosion, as well as in dredging operations.

In both cases, DP has another trick up its sleeve in the form of an auto-track function, which enables a vessel to track accurately along a line defined by the waypoints of an earlier survey.

I suspect the clever people who developed the first DP system for the Eureka Field could not have imagined that more than 47 years later their brainchild would have become the enabler of an entirely new era in offshore oil and gas production.

Oil and gas exploration in many parts of the world has moved way beyond the reach of conventional moored drilling rigs, so deepwater developments in the Gulf of Mexico, offshore Brazil, West Africa and the UK west of Shetland have really only become possible because of the way in which DP enables mobile offshore drilling units to be set squarely and securely over the well during drilling operations.

HOLD STEADY

I'll never forget the first time I watched a shuttle tanker inching towards a floating production, storage and offloading unit (FPSO).

The sky was black, the sea heaving with a constantly lurching swell and yet the tanker was able to close up on the FPSO with what appeared to be mathematical precision.

The reason, of course, was DP.

The technology not only kept the FPSO constantly weather vaning around its turret moorings to maintain a steady heading to the weather, but also enabled the shuttle tanker to make a safe and accurate approach so that its loading hose could be connected.

Offshore loading, whether via a tethered buoy, submerged turret, fixed tower or FPSO, always carries the potential for an environmentally damaging spillage – a risk reduced through DP's role in enabling precise alignment of the loading hose and minimising the chance of a collision.

Year by year new uses and developments are being found for DP.

Wherever there's a need for a vessel to hold its heading and position with near-pinpoint accuracy, you'll find a DP system quietly going about its business.

And that, in turn, means that more career opportunities are opening up for the people who will design, develop and operate the DP systems of the present and future.

It's the right place to be.