Bourbon Dolphin capsizes

Initially I thought of the possibility of the chain snagging in the locker on the rig, but dismissed it as at that length the catenery would maybe have caused the boat to stop but I doubt if it would be more!!

Similar experience in shallower water (forties field) years before when running anchors the other vessel came up hard - all standing! the backend went under the water (covered the roller and a short section of the deck momentarily)! On investigation it was found the cable had knotted in the locker of the rig and jammed hard in the pipe! Lots of smoke **** and cursing but nothing else! Come to think of it she was some distance away so in retrospect it is possible it might be possible .........

 

I've been away for a few days, just catching up now.

When Mike/Walrus stated earlier that there was no point in reviewing the design data and modeling based on stability calculations, it seemed to me that he has a valid point, although, in true Walrus style, he perhaps "went overboard" a bit. Rayk's question above addresses the same point: based on various witness accounts in the preliminary hearing, it appears that a series of events occured which placed a load on Bourbon Dolphin well outside her design limits and prudent safety factors. This abnormal load, i.e. the sudden shifting of close to 300 tons of force from the rear deck to the portside close to the winch area, is what caused the ship to capsize. While all factors must be investigated carefully by the board, which will review the design and stability calculations, it does appear that operational factors, rather than design factors, contributed most to the disaster.

To put it more simply, the ship was placed in danger by a series of events, some of which were the result of poor decisions.

I think Rayk is correct. The recommendation to lower the starboard pins would only have been made as part of an attempt to get the vessel out of trouble.

One possibility is that the intent was to shift the chain to port and secure it between the port pins, allowing BD to turn to starboard so she could apply full power to move back to the proper position. She was being pulled to port, and at the current heading she could not generate enough power to stay in position. Shifting the load to the port pins would increase stability in a starboard turn; the load would begin to lead off to starboard as the tug's head came around. Once she was headed opposite to the main force she could head straight upwind/upcurrent to get back in position.

Pure speculation, I know. But I am convinced that Mike is correct: the answer lies in the maneuvering. Rayk is correct also: the recommendation from the rig had to have a purpose. I think preparing for a hard turn to starboard by shifting the chain to the port pins is a possible reason for lowering the starboard pins. That the maneuver resulted in the chain's snapping all the way across the deck and around to the port side was the unforseen and tragic result.

 

The picture linked below shows, I think:

1. The large forces involved in rig anchor handling. Look at the deckhands and the size of the gear. Handling all that, very precisely, in seas ranging upwards from 2-3 m is a difficult and dangerous task.

2. There is a noticiable difference in size and design of the towpins on the two tugs shown. Mike pointed this out earlier, and this picture shows that the difference can be significant.

http://www.shipsandoil.com/PicoftheDay/Picof the day images/Tony Poll 061031.JPG

 

Hello Gentlemen

If the chain had been fed from the port locker and an force was applied from underneath the starboard side like possible the lenth of chain and anchor and possibly the HV regain pressure on the chain in a lower section of the chain so now you have a loop sort of speak .The tension on the chain be removed for a brief moment and then reinstated creating an almost sling effect. The precureser to the roll? How Much chain was released at that moment from the Rig if you calculate the forces of a stuck anchor release and "dropped " we would have a a situation where the load of the Bullard pull from the second ship and the anchor chain and anchor all placed on the BD at the same moment this would certain explain the unusal effects that are being reported including the slow release of the emergency release
I would like to know what HV was doing during these moments what was their location were they tring to regain some of the chain? could this be the "Snag"
I have followed the this unfortunate event since April 12 at 5:21

I handle alot of anchors in the Gulf found the work to intense for the old MV Rivers Inlet so went back to deep barges and transfers

With all due respect
Capt.F Laursen (RT)

 

One thing is painfully obvious (to me at least) given the sizes of chain etc and the depths I DO believe thaty those boats are far to small for the job! the original (?) plan when I left the industry some seven years ago was that in the west of Shetlands (DEEEEP water) the idea of using rigs and chains was imposible drill ships on Dynamic Positioning would be the only way to go!! what happened cost to high? so What is the Price they are prepared to pay? What's the lives per ton rate at the moment and is it on the increase/decrease? In other words how much does the world need oil? (Don't forget there's other parts of the world were people are dying for oil - they may not know it but that's the prize)

 

Mike,

One fact I've noticed in the past few years that supports your statement is that more fleets are adding 20,000 bhp + and approaching 30,000 bhp anchor handling tugs. Every AHTS Maersk has built since 2000 has been 24,000 bhp or more. No one is adding that much power unless there's an absolute requirement for it. If anchor handlers that powerful are being placed in service for depths of 3000 ft and more, then it follows that 16,000 bhp tugs like Bourbon Dolphin may be marginal, at best, given the weight of chain to make a secure anchorage at those depths.

 

In the GOM we moor at 2500m routinely, however with suction piles and synthetics, not anchors and chain.

State of the art is not particularily relevant. The new Boeing 777 is a state of the art aircraft, but it is not designed to fly to the moon. The operator must use the equipment for what it is designed to do. As a designer of this type of vessel, there is no way that I can anticipate every operational situation that the operator can put a vessel into. I have to trust that the operator uses sound and purdent judgement in selecting jobs that the vessel can do, or at least have the good judgement to confer with the designers when they are unsure of the vessel's true capability.

On the increasing of HP in recent designs and consideration that the BD might have been underpowered, I personally don't think that this had a real contribution to the accident. I don't see how more power would have got them out of a situation that they should never have been in to start with. The only impact that more power could have contributed is that with more HP the vessel as designed/built likely would have been too small to handle a greater HP and therefore the vessel would have been physically larger and therefore more suited for the job.

My opinion only...........

 

Acsearch,

I didn't express my thought as clearly as I might have. I did not mean to imply that BD was underpowered as a design. I was using horsepower ratings as one indicator of boats more powerful overall. The ones I spoke of, the Maersk A Class and many newbuilds with 23,000 bhp and more, are proportionally bigger in length and beam, with more powerful winches, more spooling capacity, bigger thrusters, higher Bollard pull, etc. They are larger boats in every respect. The original plan for anchoring at this depth with chain had BD in an assist role. This seemed to take her capabilities into consideration. Changing her role at the last minute from assist to primary tug seems like a case of using the tools available, rather than the proper tools, for the job. As you said, the designer has to trust that the operator will use sound and prudent judgement in selecting jobs within the boat's design capabilities.

 

hi again .I have another question that may be out in left field. I do know a little bit about lifting and crane work on land and im trying to find out if a strong curent pushing sideways on the cable and the bd would be like wind loading on land .it might sound crazy but wind load on a very small piece being lifted can make that piece go off center by alot. the cable in this case being very long and having a good curent runing would be subjected to large sideways push would it not. Would that explain the bd being hauled towards the other anchor and not being able to keep course .Would it also explain why the cable went over the side so quick if that is what happened when the pin was dropped. Sorry if that dont make to much sence .

 

The simple answer is yes; current adds to the dynamic load pretty much in the way you described. The force is significant, since water is so much more dense than air.

 

Guillermo,

Our revised lightship: W = 2673 T, VGC = 25.6'
These values are based on the IMO 10% burned out condition with 740 T of deck cargo 1m abv deck.

The height of the VCG is reflected by the drop of deck cargo capacity: 740 vs 800 as per Sales Dept. spec sheet.
The additional equipment weight is also reflected in the 2130 T deadweight vs 2500 T @ 6.5m LL as per Sales.
This info is just to help you 'calibrate' your model and has no bearing on the stability at the time of the accident (especially since the deck cargo was only ~ 20T). These boats can easily meet IMO stability criteria depending on tankage status (from stiff to tender). I suspect the tankage they had selected was for a slow comfortable roll.

 

Thank you, smartbight. Too busy and tired these days, I'll be a little slow to work on the simulation and post results.
Chhers.

 

Ace, Charlie - thats what I said wasn't it? the jobs getting to big for the boats UNLESS specific boats are used! and using the correct tool for the job is down to the tradesman not the builder/maker of the tool! So Ace mate no matter how you design the damn thing if the user uses it wrong it will go wrong and theres not a damn thing you can do about it! the only thing is that (theoretically at least) if that happens the designer can't be blamed!! He will be but he shouldn't be!

 

Hi SmartBright
Attachments are excel work book for 2 types of vessels, one an old UT 704, and the other a new 66m AHTS.
I made the work books as the stability information for conditions was very limited and doing a manual work up was not practical considering the time constraints we were often operating under. The New vessel had half the conditions that the old one had!
There may be errors in the work books and I'd appreciate them being pointed out!
I tested them against the vessels stability book conditions and found they worked out very close - giving a more conservative answer as I did not have the full model to work with.

Maybe it is time for the IMO, Class Societies, Flag Administations to require all vessels to have a stability program onboard. Not to mention updated criteria for towing and something for Anchorhandling - ie depth of water limitation, weight of gear. Or is that going to far???

I also have a workbook for an older American built AHTS 205ft LOA - I will tidy it up and post it if people want me too?

 

Smartbight,
My colleague Javier Cordeiro is performing some stability calculations on the vessel I mentioned before. It is an offshore tug with the same appearance and layout as a last generation AHTS, except for the tanks. Size is a little bit bigger than the BD (83.0 m LOA, 17.6 m BMax, 8.7 m moulded depth).
At the departure from port condition for this vessel (100% consumes, no paying load, 4289 t), which has the lowest GZ at 30º, and considering lightship's condition's VCG at deck height (8.7m), a hanging load of 330 tonnes acting at the staghorn produces a heel angle of 29.5º.
Calculations have been done using Hydromax.
Making a rough and quick estimative based on the posted curve, around 460 tonnes are needed to turn it turtle.
We'll revise this and next week we'll post something else (Javier promises!)
Cheers