Bourbon Dolphin capsizes

Bra jobba Stian

 

Let's review again what Charly posted:
"According to witnesses, as the vessel headed away from the Transocean Rather drilling rig with one of its anchors, it seemed to turn sharply and the anchor chain jumped out of the mechanism at the rear of the deck which held it. As the chain ran across the deck, the 75-metre tug lurched one way, then the other, before overturning."
It seems this does not coincide with the explanation in the sketch...
So...anchor on deck...rode chain attached to drilling rig....quick turn...rode chain shifts to the side....vessel heels....anchor slips also to the side...vessel capsizes....
Weight of chain hanging between vessel and drilling rig enough to turn vessel turtle....? Extra pull from the rode as the vessel turns...? Also flooding contributing...?
More info, please!

 

I'll certainly watch TV tomorrow night!

 

You're right, Guillermo.

The sketch does not explain what caused the rode to "jump" out of whatever restraining mechanism was used on the tug's rear deck. Also, several sources have said that standard practice when the tug is near the rig is that the rig winch holds most of the rode length, paying out as the tug moves away. If so, there might have been as little as 30-40 tons hanging from the tug. I keep coming back to a force at a wide angle from the line between the tug and rig, wondering if the rode snagged somehow. That would cause an off line force equal to the power of the tug's engines, which might explain both the sudden turn and the line's jumping out of a restraint and veering to the side.

One other point, on the question of flooding: photos by Ebbe Holsting show large air intakes located outboard at the rear of the deckhouse of the Maersk tug on which he worked, starting close to the deck and rising almost to the top of the structure. A similar placement might have been made on Bourbon Dolphin (speculation, but I have not seen them visible in the front and side view photos of Dolphin) The outboard location means that they might be subject to flooding at an extreme roll angle. Not as much water ingress as an open WT door, perhaps, but with the added effect of killing the engines whose prop is still in the water, eliminating any possible chance of "powering out" from the instability.

Anyway, everything is speculation until the investigation is complete.

 

Stian,

Thank you for translating the sketch captions!

 

Raggi,

Take very good notes, you'll be getting a lot of questions from us non-Norwegians after tomorrow!

 

Interesting....what could have been?

Joky note (with all respect to the casualties): Be careful not to open here a door to that that kind of speculative USO (Unidentified Submerged Object) explanations that flourish in the media when a sinking remains an unsolved mistery.

 

OK, Guillermo, you opened the door, (and this is directed at the press, not to take away from the genuine tragedy of seamen dying) as we say in the US, I'll mention the elephant in the room, the most popular USO always..... nuclear submarine ... very surprised no one in the popular press has asked that question yet.

 

Hi Charmac,
Engine room air intakes will (on the AHTS vessels I have worked) allow more water into the engine room than an open water tight door, see my earlier post

( - engine room blower intakes - at what angle did down flooding occur though them in the case of the Bourbon Dolphin? )

From the trim stability book of a 2005 built AHTS the Flooding angle has a min of 46deg, is this enough?

Many of the new builds I have worked on have the engine room air intakes outboard and low down, is this a contributing factor in the case of the Bourbon Dolphin?

On another point - the last AHTS I worked on had stability conditions listed in the stability book and when I looked closer found that 1 had the vessel well overloaded beyond her tropical marks and 2 more had the vessel trimmed too much by her stern (Max Draught Aft exceeded) and another condition was using a different light ship figure - the difference was very small but these errors led me to doubt the rest of the data in the book.
Could there have been errors in the paper work and the officers used the approved book and this led to a dangerous condition that normally would have caused no danger but when things went wrong resulted in what we have seen?

 

Riggertroy,

Your points are all possible contributing causes. I've checked several of the references cited by posters here. I am amazed that there appears to be no language dealing with stability calculations for the specific conditions of anchor handling. Even the paper from the 2005 Singapore conference, which begins by discussing the increasing role of anchor handling as a major function of modern offshore support vessels, does not list anchor handling among the various subdivisions of stability requirements which it later recommends be reviewed and updated! I see regulatory conservatism and reluctance to acknowledge new technology in the drinking water business all the time (technologies with multiple installations dating back 10-15 years are called "unproven"), but somehow I thought ship safety regulations were kept up to date. The dynamic forces introduced by offshore anchor handling are dramatically different from normal cargo carryiing. It's difficult to believe that there are no specific stability requirements for this function.

 

Thanks for pointing to the air inlets on the Maerks boat (shown below). I never looked at those pictures in detail but they have to be on the B.D. too. 16000 bhp needs a lot of fresh air and it has to come in through large openings. On the pictures it looks like they are at 40 deg. which is the minimum required for down flooding. Once the boat rolled past this downflooding point and stayed there on the side, progressive flooding started.
I am sure everything was buttoned down on deck. Those Norwegian crew are pros and they all know what happen when a hatch is left open.
We will modify one of our GHS model to match the B.D. and see how it respond under all the different scenarios discussed.

 

Is the figure for down flooding (40degrees) fixed or is there an allowance made for vessels where down flooding occurs before that? I'm sure I've been on vessels (older supply boats - funnels aft) where down flooding would occured before 40deg.

 

Stevns power accident

Attached is a report on the Stevns Power Accident, does not draw any firm conclusions on the cause of the sinking, but gives plenty for thought.

 

The weather was not too good. If the crew for some reason decised to use the tow pins it could have ben lifted out if the angle off the wire was right.

I was not thinking about this, but if the rig also is using it's own winch it's posible that this could have hapend since then the load would not be directly under the ship, but betwen it and the rig somewhere.

Maybe after this a-frames will be more used.

I'm keeping a eye on ulsteins own home pages since I think this will be the first place reabile information will show up. http://www.ulsteingroup.com/

 

A MARITIME trade union is urging the Norwegian authorities to examine the design of the Bourbon Dolphin as part of the ongoing accident investigation.

According to Nautilus UK ­ which represents 3,500 North Sea oil workers ­ the loss of the Bourbon Dolphin is similar to an accident in 2003 off the coast of Nigeria in which the Danish Stevns Power capsized while carrying out anchor-handling duties.

Eleven people lost their lives in the accident. An official investigation into the incident by the Danish authorities found that the Stevns Power capsized in less than a minute after water flooded onto the deck and into the engine-room during a turn.

The report also highlighted problems including the training and experience of officers, fatigue and time pressures.

A statement issued by the trade union this week said: "Nautilus UK is concerned that lessons from the 2003 disaster have not been learned and believes that the investigation into the Bourbon Dolphin needs to consider such factors as ship design, commercial pressures, seafarer fatigue and training."

Nautilus's head of communications Andrew Linington said that the union was concerned by the generic design of anchor-handling supply boats.

Mr Linington said that the investigation should look at issues such as the fitting of quick release mechanisms which would allow tugs to rapidly jettison anchor cables in an emergency.

But the suggestion of a link with the sinking of the Stevns Power has been rejected by Bourbon, the owners of the Bourbon Dolphin.

A spokesman for the Paris-based company said that the two accidents were "not comparable" as the Stevns Power was an old boat when she sank, whereas the Bourbon Dolphin was less than six months old and was fitted with all the latest technology.