Bourbon Dolphin capsizes

The oil companies certainly go to great lengths to keep their safety records clean, even in underdeveloped countries. Managers bonuses can dissappear if they have bad incidents on their patch because the company can be denied access to bidding for new exploration blocks in many countries. Responsible governments always demand access to their records before letting them bid for new acreage. If there was a company man on the drilling rig, then they will have some responsibility.
Some deal could be done whereby the UK and Norwegian governments raise a tax deductable levy across the industry and also contribute themselves, if it gets to the stage where a detailed ROV survey or even a recovery operation become necessary. As things stand, a lot of decisions are being made based on witness statements of what happened. The answers to what caused the incident may be in the wreck.
ROV's have cleared up the cause of many maritime disasters. I am thinking of the Gaul and the Derbyshire in particular, that were mysteries for years but now we can be pretty sure of what happened and why.

 

Murdo I see what your sayin, but ..........

And I ain't so sure about the 'Gaul' no matter what the so called evidence sez (don't ask why, I just ain't) but that's a different job!

 

I think there is a misconception about the capabilities of the vessels and the 'size' they need to be. I am very confident that my vessel would be fully capable of working the TO Rather chain in 3500' of water (which we have, in fact, done a few times in the GOM (both the TO Rather, and her sister rig the TO Richardson). It is not the size, or power, or even the 'capability' of the vessel that determines the safety of the operation involved. We have been maxed out on power countless times when setting the anchors, picking up the anchors, or trying to hold position in current with our two puny 600 HP tunnel bow thrusters screaming. We have had to get creative - including reducing power until the chain is on the mud (which reduces the force being acted on the vessel) and then repositioning back over the line and giving it hell again until we are too far off line again. It isn't fun, but I have never felt in danger.

The vessel I am on is quite similar in size to the BD, with less power, less winch capacity, less bollard pull, but has been working safely in water over 5000'. It is a very stable boat and has been used as the primary vessel on many moves.

I believe that the major problem of these newer vessels, like the BD, is that the boat and Oil companies want to jam more stuff on them. Bigger storage reels, larger ROV spreads, etc. which makes for far more weight aloft. It gets to the point where the capabilites of the vessel are more than the hull can handle from a stability stand point. The newest and largest vessel in the GOM, the Laney Chouest, leaves port with everything maxed out for storage. It is a very capable vessel, but at full power with everything full she may be a very dangerous platform. Who knows?

Does this make sense? I don't know if I made my point very well. I guess it is like having a small tug that is very stable moving a large barge around. It may be slid sideways and pulled around a bit, but will get the job done - whereas a large tug with more capability and power but less stability may be tripped and sunk if the barge gets around and girds it.

--Chuck

 

Sensible post, Chuck. Unduly rising the COG is not a good recipe at all.

 

Sometimes the best ship for two jobs, is two ships....

 

Yes, I agree. The professional tug members all seem to be happy with the size of the vessel.
There is something else that was mentioned previously that bothers me. When the bridge survivor was giving evidence he said that at one stage with 1500 mtrs of chain out they were registering a 'high' tension of 180 tons, they had called in the assist vessel at about 140 tons. About ten minutes before the capsize they had 1800 mtrs out and the tension went to 270 tons after the assist vessel again lost the grip on the chain.
Immediately prior to the capsize, just before they dropped the towing pin, they were at 330 tons.
I have read somewhere on here that the chain weighed 160Kgs/mtr so their share of the load would have been 144 tons and coupled with the Bollard Pull of 194 tons they should have had a load on the winch of about 241 tons from these two components.
Could the wind and tide account for 89 tons? If not, or if there is no other significant force at play, the figures don't add up

Murdo

 

Some more info on bigger vessels:

Green Anchor Handling
Six large and environmentally friendly anchor handling vessels, designed by Vik-Sandvik, are being produced by Kleven Verft in Ulsteinvik. The work is being done under contract with Siem Offshore Inc of Kristiansand. Siem also holds an option for another six vessels.

The ships are sophisticated anchor handling vessels, 91 metres long, with 22-metre beams and engine power of 19,000 kW (28,000 Hk). The combination of environmental friendly design and large capacity helps these craft to be especially well suited for North Sea operations. A key to this kind of performance is the vessel’s reinforced hull for work in icy conditions, and preparation for A-frame and ROV garage works.

http://www.klevenmaritime.no/index.php?page_id=1014

 

Another 'big boy', the Rolls-Royce's UT-751-E. On an overall length of 93 m and a beam of 21 m a cargo deck area of about 1,100m2 is available, and the deadweight is approximately 5,200 dwt at the design draught of 6.2m.

Read: http://www.rolls-royce.com/marine/downloads/article/vis_ut751e.pdf

 

Not that big, neither an AHTS (just an OSV), but recently launched in Astilleros Gondán, Spain: The EDDA FRAM for Østensjø Rederi A/S. See http://www.ostensjo.no/ostensjo/web.nsf/pages/EddaFram
The propulsion and steering is by means of two diesel-electric driven Voith propellers.

Also H.J. Barreras, in Vigo, has been assigned a contract to build four X-bowed seismic vessels for Eastern Echo.
See: http://www.marinelog.com/DOCS/NEWSMMVII/2007may00310.html

 

Here the Haviard 845 for Havila Shipping ASA.
http://www.havila.no/default.asp?menu=72

Loa (m)- 92,00
B (m)- 22,00
Draught max (m)- 7,50
DW at max draught (ton)- 4200
DP- AUTR
Deck Cargo (ton)- 1500
Deck Area (m2)- 750
Speed 100 % MCR (knots)-17
Speed economical (knots)- 13
Bollard Pull (ton)- 275
Total power installed- 20700 KW

 

Eminent sense, Chuck. You made the point well that stability is paramount in a working tug of any size. The photos you've posted here of your vessel demonstrate your point well. Compared to many of the newest vessels, her superstructure is both lower and (to my eye, anyway) less massive. You're probably right that as construction and operating costs rise, there are pressures to cram more "stuff" onto each hull.

Thinking about what a tug is supposed to do, as you said, pushing, pulling, getting dragged backwards or to either quarter ... stability would have to be the prime attribute in a design .... until the bean counters and the "cost engineers" arrive.

 

Murdo,
89 tons seems too much to me for wind and waves. Probably it has to see with the angle of the chain line.

 

Guillermo,
I have no working knowledge of these vessels although I have observed them at work dozens of times, the boredom on the platforms make anything interesting. I work on the vessels in port quite often adding and removing ROV spreads, A-Frames, Tugger winches, etc. so I know my way round them if nothing else.
What I have not seen in any report is the time that elapsed from when the assist vessel lost her grip on the chain and the time of the incident. From what I have read it seems to have been longer than 10 minutes. I can understand the tension going to 270 ton when the chain came out of the hook, the vessel would have been pulled backwards by this load but everything should have levelled out at about 230 tons (my previous figure of 241 did not allow for the weight of chain in seawater).
Was the witness confused and remembers 230 as 330? If the skipper and the mate were aware of this extra 100 tons why did they agree to lower the pin at that stage? What is broadwise tension that is mentioned in the safety flash, is this the transverse effect of tide and wind, and how high can it get? Is it a vectored add-on to the Bollard Pull? I have read somewhere that Bollard Pull is lowered by power going to thrusters.
I have watched a strain gauge on the mooring line between a FPSO and a 100,000 ton shuttle tanker and it seldom goes over 20 tons in normal weather.
Has anyone here experienced this amount of tension from a suspended chain?

Murdo

 

Chuck and Charlie - let me add my puny weight (as an ex mate) to that! Totally agree with you Chuck. When I spent some 17 years shoveing oil stores and rigs around it was ever thus! "Come on Cap'n just another two lifts!" was the usual cry! "We could put it on top of those lifts over there - stability? that's your problem cap'n we don't understand that, but if you don't do as we say, we'll get a skipper who can!" (and the only reason he will a lot of the time is because he is still not fully experienced and is still 'pushing' a little!

Yep and in the old days (when the mate ran the deck [by being on the deck] rather than was the second driver)I've walked off the deck a couple of times taking the crew with me - too bloody dangerous and the 'old man' was dithering because of the above problem! It does help him, but.........(ater all if your crew won't work you can't do much can you!!! It puts an enormouse strain on the mate too! (yeah I often looked in the 'Sits Vac' colume but when it came to it was usually vindicated!!!

 

After writing the above I realize that the transverse force from the wind can be substantial. I have tried to pull small vessels from midships onto a pontoon against a beam wind more than once and failed. I can imagine that a cross tide would be even stronger, so it could be that this 'broadwise tension' could cause the high load showing at the winch.
As all the forces end up in the chain, the catenary will be lifted as the tension increases. To decrease the tension, either more chain must be introduced or the vessel has to move backwards.
The first witness reports had the vessel turning sharply to starboard before overturning. The bridge survivor also reports the captain turned the vessel to starboard and that the tension dropped letting the mate drive the pin down.

If the tension was dropping then the vessel had to be moving astern, or in the direction of the chain, at the time that the load was allowed to transfer to the port side.
As Capt. Chuck has told us from his experience that moving backwards lowers the stability and given that this vessel had been known previously to have had stability problems, the shift in load at this point proved to be fatal.
There were probably other factors that contributed to the loss of stability, but that would have been the final straw.

Murdo