Dynamic Positioning: Should I rely on DP 2 or DP 3?

In the last article, we pointed out why the offshore industry needs dynamic positioning and what challenges shipping companies are facing as a result. However, there is an even safer dynamic positioning system called “DP 3.” As described before DP 2 is used in avoiding a fatal single point of failure by providing the ship with redundant systems.

For example, a ship with DP 2 might have two, three or more separated engine rooms, separated switchgears and further critical equipment. Therefore, even a fire within one of these engines rooms would not take the vessel out of service. Using three engines rooms and losing one completely to fire casts the ship back to 66% operating power.

As long as a service ship can use DP to stay on a certain spot, it does not have to abandon its tasks. How precise and stable (wind, waves) the DP needs to operate depends on the kind of required service.

What is Dynamic Positioning 3

Dynamic Positioning 3 provides all the single-point-of-failure-safety that DP 2 does, but avoids, in addition, being beheaded. DP 3 vessels own a second bridge and are therefore, able to operate under all circumstances. As a shipping company and as a charterer, one needs to ask the question: is this really of use?

Which leads us to the interesting question: how this…

The Mumbai High North Field; Copyright Owner unknown, please contact us when you are the owner; Source farm2.static.flickr.com/1097/1463943403_f315fee022_o.jpg

Becomes this…

Burning rig; Copyright Owner unknown, please contact us when you are the owner; Source www.canadian-wellsite.com/images/Photo%20Gallery/BFM/bp1.jpg

The burning rig in the picture is the Mumbai High North platform, which became a disaster for the entire Indian Oil Industry and took 22 lives. MHN was the processing platform of the Mumbai High North Fields, formed of four platforms interlinked by bridges.

A cook, two fingers and a gas tank

The incident started as the unlucky cook of the multi-purpose service vessel “Samudra Suraksha” cut off two fingertips while preparing food in the galley. Bleeding heavily and being in shock, the cook was to be transferred in a basket by crane to the MHN platform where he could undergo medical treatment.

Before the accident the MSV Samudra Suraksha was supporting a diving operation. “While approaching the MHN on the windward side, the MSV experienced problems with its computer-assisted azimuth thrusters so the MSV was brought in stern-first under manual control and the injured person was transferred off the MSV.” Source: home.versatel.nl/the_sims/rig/mhn.htm

During this operation, strong waves pushed the helicopter platform of the MSV into the external gas export risers, crushing at least one of them. The gas shot out, flushing over the helideck, hitting the bridge and igniting. Drifting below the Mumbai High North Platform, the fire ignited the other four external gas risers, the 10 fluid import riser and shortly after, the whole platform.

MSV Samudra Suraksha after rimming some gas export risers; Copyright Owner unknown, please contact us when you are the copyright owner; Source farm2.static.flickr.com/1397/1464798756_fb1b282587_o.jpg

DP 3 Necessity

When the multi-purpose service vessel approached the platform, it had just come from a 60-meter deep diving mission and was holding six divers in its pressure chamber. As it was impossible to open the pressure chamber without killing the divers, the crew of the MSV Samudra Suraksha had to abandon them. Before the crew left, they lowered the air pressure to 80m depth as they assumed the ship would sink to the ground, which might enable the divers to escape, granting them a minimal survival chance.

As it later turns out, the vessel was floating away from the scene. Emergency units started a dangerous rescue attempt by cutting the chamber open, running the divers over deck of the rescue boat to a special pressure chamber and throwing them in, hoping for the best.
All divers were rescued after 36 hours in the MSV.

Does the offshore industry needs Dynamic Positioning 3? Yes, because a vessel without a manned bridge has no use for redundant engine rooms or switchgears.

The Mumbai High North Field incident cost 22 lives, causing the loss of two platforms, a 100-meter long service ship, one helicopter and 10% of the annual Indian oil production. Despite this, an oil spill had to be contained as a huge amount of gas leaked out because of some 12km long risers having been damaged. They only possessed two emergency shut down valves (one being at every end).

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