Bourbon Dolphin capsizes

Discussion in 'Stability' started by Crag Cay, Apr 12, 2007.

  1. Guillermo
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    Guillermo Ingeniero Naval

    To be accurate and of real use in an emergency, stability computers need to be continuosly monitoring and inputing tanks levels, (or then draughts ahead and astern), heaving amplitude and rolling period, as well as how much time the vessel 'sleeps' at the sides of the rolling movements. Previously the program has had to be fed with data and adjusted aboard for a long time in operating conditions, so the program 'learns' about the difference between the natural period of rolling and the waves' induced one. Also not movable cargo has to be previously input. For a fishing vessel this can be even more tricky as they lift weights (nets,etc) when at sea. I don't know how the programs presently used aboard work, but what I know is that the mathematics for the computing routines to integrate all this are not an easy task.

    As a matter of fact I know at least one programs developing company that wasn't able to solve the whole of the problem and went for simplified versions that really only offer a clue to what's happening (no that it is of no use, of course, because it advices the master something may be wrong, but it is far away from 'perfection').

    Somebody can explain how the present stability computing for AHTS vessels works? (Other than Chuck's spreadsheets..;) )

    Cheers.
     
  2. riggertroy
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    riggertroy Senior Member

    Last offshore company I worked for had the attitude that as a computer program (even an excel spreadsheet) is not mandatory the company is not going to supply (pay for) one. A few companies may pay, but I would say most will not. Hence I make my own easy to use spreadsheets so that we can quickly check the vessels stability and prework loads, who here works their vessels stability out long hand using pen and paper?
     
  3. Nigel1
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    Nigel1 Junior Member

    Stability Program
    The company I work for has the same program fitted on all the anchor handling/supply vessels. On the newer vessels, those fitted with tank data/sounding systems, the tank sounding system is used as an input to the stability program.
    The program is based on the data from the Stability Booklet, and the program is Classed, and is included in the annual Load Line Survey, where various conditions from the stability booklet are compared to conditions inputted into the computer.
    Since the BD incident, the program has been modified with an anchor handling module. The operator inputs the expected static weight of the mooring system, and from this, the program will show the maximum bollard pull which the vessel can use to stay within the limits of the criteria laid down by the NMD. A margin has been built in for expected dynamic forces.
    In a previous post, I put up a screen shot of the program


    Murdo,
    Yep, your right about simply extending chain lengths in some cases.
    Newer rigs purpose built for deepwater work are built with much larger chain lockers and more powerful winches. This avoids the vessel having to locker any chain from the rig, and more importantly, does not need to have the rigs anchor on deck. Some rig operators have gone to the trouble and expense of converting older rigs to deepwater capability by fitting larger chain lockers and bigger winches. As an example, a few years ago we worked a 25yr old rig which had been converted to deepwater work, and we moored that rig in 2200 meters water depth using a conventional wire and chain configuration. No chain was on the boat. The whole operation was carried out with the vessel not exceeding 60% of maximum power and the maximum winch load was in the region of 150 tonnes and only when stretching out the system prior to landing the anchor on the sea bed.

    In other areas of the world, notably off Brazil, the use of prelaid systems is now common (I dont know why the MSF says the use of prelays is not practical). The prelays use either specially designed vertical lift anchors (anchors which remain embedded even with an upward force), or torpedo (suction pile) anchors. To these are fitted either wires or a combination of wire and soft rope, and moored off with a buoy. With the rig on location, the rigs wire or chain is then pulled over to the buoy by the anchor handler, the buoy is then decked and removed , and the two parts of the system connected on the deck of the boat and then released overboard.

    With the present proposals by the NMD and the MSF, anchor handlers will be graded, and in the North Sea, they are now audited prior to any rig move. Boat owners/operators now have to be supplied with full details of the mooring operation at the tendering process to see if their vessels are suitable.

    However, as you said, there are still rigs out there not designed for deepwater work, but are none the less working in deepwater, putting boats and crews at risk. I hope that one day, this issue will be addressed, and we can do away with 2 or more boats working on one anchor and having to use J Hooks and grapnels
     
  4. murdomack
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    murdomack New Member

    Hi Nigel

    It's good to see from your post that some moves are being made in the right direction.

    Thinking about your comment the other day about old drilling rigs, I wonder if the BD inquiry has led to required improvements and regulations for the Anchor Handling Vessels but missed out the equally much needed upgrading of deep-water rigs and their anchoring systems.

    Maybe the focus has been too intense on the shortcomings of the sunken vessel to realise that it was not necessarily the sole cause of the tragedy.
     
  5. Guest-3-12-09-9-21
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    Guest-3-12-09-9-21 Senior Member

    The TO Rather was actually in the Gulf of Mexico and I have participated in moving it numerous times in water depths over 3500'. The big problems with the TO Rather and the TO Richardson are that the winches were absolute garbage. It was not uncommon to be stuck on a leg for over 24 hours while the rig crew scavenged parts from other winches to get the one winch operational. To get the winches to pay out it was often required to pull at very high power settings to get it to dynamically pay-out. I also remember that the mojo (chain/wire connection) were huge - the chaser had a hell of a time going over the connection. I was stuck for over three hours once wearing out a little stretch of water trying to get the chaser to get over the mojo so I could get back to the rig.

    Not sure what the operations of the BD were doing with the adding chain, but the rig itself should have been able to handle that mooring depth without any troubles.
     
  6. Nigel1
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    Nigel1 Junior Member

    Hi Chuck,

    Seems to be a common problem with Transocean rigs, winches come second place to drilling equipment.
    I believe that at the time when the T.O. Rather was working off the Shetlands, the boats were using J Hooks to break out the anchors as they were having problems getting the collars over the mojo.
    One method I used with the Scarabeo 7 which had similar mojo's was to get the mooring master to calculate the actual depth at which the mojo lay, and then when chasing back, would shorten the work wire so that the collar was at the same depth, and then trickle the boat slowly over the joint. That seemed to work, and the Saipem guys were well happy as they reckoned that previously, boats had been stuck on the mojo's for up to 6 hours
     
  7. Guest-3-12-09-9-21
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    Guest-3-12-09-9-21 Senior Member

    The method we used to get off the mojo was pull like hell after we got stuck and then throw everything in neutral and slingshot back...at some point there is a pop and the chaser shoots over the mojo. Sort of caveman techniques, but effective nonetheless. By pulling hard the chaser gets jammed on the bottom end and the top of the chaser is over the top of the mojo - then when the power is reduced the system relaxes until, at some point, the bottom of the chaser pops over the bottom edge of the mojo.

    Brute force and ignorance sometimes works better than finesse...which is good for me.
     
  8. Guest-3-12-09-9-21
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    Guest-3-12-09-9-21 Senior Member

    It is interesting reading the anchor handling manual - for the most part it seems fairly well written. The one big difference I noticed is that the scope used to run out seems somewhat overly long. We have been using 1.2 X water depth for working anchors in the GOM for years now and it seems to work well. It is usually possible to pull the anchor off bottom even without shortening up - I imagine this is written for shallower water depths as a rule.

    Most of the rig moves we are involved in anymore are 4000' to 5500' for this class of vessel. The difference in 1.2 and 1.4 is fairly substantial at these depths.

    The stability section is a good read..makes me wonder what is going to take place over the next few years in the US. There is really no push that I've seen to even address the stability issues of the BD.
     
  9. Guest-3-12-09-9-21
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    Guest-3-12-09-9-21 Senior Member

    Here's a video showing a typical stern to stern transfer during anchor operations in the Gulf of Mexico. You have to get close enough to pass a heaving line between boats and then keep them apart when the load is transferred between vessels. Makes for some exciting times when things go wrong.

    http://www.youtube.com/watch?v=puY0gmGlY_s
     
  10. Guillermo
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    Guillermo Ingeniero Naval

    Chuck,
    It seems there is (or I have) a problem when trying to access the link you posted. It takes a tremendous amount of time to download, making me quit in desperation. Has any other member experienced also this difficulty....? :confused:

    Cheers.
     
  11. riggertroy
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    riggertroy Senior Member

    I had no problems, wroked well, was able to show the wife what I used to work at, thanks :)
     
  12. Guillermo
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    Guillermo Ingeniero Naval

    It seems to have been a temporary problem here. I have been able to access and watch it without problems now. Thanks a lot.

    P.S. I have been watching your other videos, Chuck. You really have a risky job on that deck!
     
  13. Guest-3-12-09-9-21
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    Guest-3-12-09-9-21 Senior Member

    My job is easy - it is my crew that has the hard job. My job is only hard if you think about the risks involved :rolleyes:
     
  14. Knut Sand
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    Knut Sand Senior Member

    The company got a 5 000 000 Nok fine (bot) for this accident.

    http://www.dagsavisen.no/innenriks/article390012.ece

    Is in Norwegian though...

    The captain were not given enough time to know the ship, the job, the crew, and the company had not good enough safety instructions, if I understand it correctly.

    edit; the crew got no blame.
     
    Last edited: Jan 5, 2009

  15. Guillermo
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    Guillermo Ingeniero Naval

    Thanks, Knut.
    So, who's guilty for the loss of several human lifes? It's just a matter of a fine? No responsible of the company is going to jail?

    Cheers.
     
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