Bourbon Dolphin capsizes

Bollard Pull and Load are 2 different things. Bollard Pull is the amount of force that a vessel can exert against an object based on it's engines and propellers. Load is the amount of force that an object can exert against a vessel based on it's weight and dynamics. The lack of bollard pull didn't capcize the BD, the load over the side did.

You will find that most large tow winches today are rated at 500-700 tns, but the vessels are only capable of bollard pulls of MUCH less. It is 2 different types of loads.

 

So many experts

I've sifted through the various comments in this thread, and can't find very much from those who are actually IN the North Sea Industry at the moment. I've worked on AHTS vessels in that region for over 25 years now, from the old tugs to the new Super Anchor Handlers, and from all the points that have been raised so far one thing is clear - this was an ACCIDENT! Whether it was caused by human error, or mechanical faults why don't we all wait and see what the outcome of the enquiry is?
All modern AHTS vessels are equiped with compter programs specifically for calculating the stability of the vessel, but is a sudden shock load is applied there is no way this can be calculated. (Can you calculate for hitting and iceberg???)
Contrary to other reports this is the ONLY accident of its kind that I know of. The Danish vessel which sank was being pulled back at a great speed when she capsized, and did not have the benefit of towing pins (I belive she only had quarter pins)

 

Not all Modern AHTS vessels are equiped as you say, I have worked on a number and found it crazy that they were not carry such programs as the nature of the work leaves little time for manually working stability.

I agree wait for the reports, but it is healthy to discuss what may have happened as it may lead to insights in to what could have caused the accident and may lead to preventing further accidents of this type.
One thing people seem to forget is that accidents do happen and no matter how careful you are, situations can build and you get to a point where so many things could go wrong that there is no "good" outcome.

 

Amazing

It would be helpful if people read what has posted about since the incident There have been many insightful posts about the abilities of the Bourbon and possibly and probably what did happen.... then some Dullard in a news room some where suddenly gets a hold of a number probably out of a spot near his back pocket and runs with it... prints in a rag and suddenly he has insight.... "give me break!! The Investigators that are working this case are the best that the world has to offer and leave no stone unturned (I know this from experience)and I am quite sure they will know the difference between dynamic load and bollard pull.... with by the way was in the neighbor hood of what she was handling I truly love these experts that just pop out of the wood work as far as I am concerned this is a disrespect to Master and men of the Bourbon they were doing a job that most can only view from a picture and can not imagine the scale or magnitude of what they did and still do out there so we can drive our cars and light our stoves and so on.... There are alot of questions I would like to see answered too about the Highland and Rig and sonar reports around the rig at the time The question that haunts me is what caused this pull to port? I can not believe that this instability suddenly showed up with not even a mention before now

Capt. F. Laursen

 

I gues that could be argued up and down in a 55 page thread all by itself.

If a generator is rated at 200kW and you pull 200kW your running 100%load.

If your running 180tonn bolard pull on a boat reated for 180tonn your at 100% off the capasety off the ship.

 

Bollard Pull VS Vertical Winch load

The point is that the Dolphin had two forces in effect: The horizontal force from her engines, and the vertical force from the weight of the chain.

The winch load is the vector sum of those loads, I believe.

To use a typical Engineering approach, explore the limits:

(1) Tug is pulling a heavy barge, applying a Bollard pull of 100T
-- Horizontal Force = 100 T
-- Vertical Force = 0 T
-- Winch Force = 100 T

(2) Tug is lifting a heavy chain and anchor, engines stopped:
-- Horizontal Force = 0 T
-- Vertical Force = 100 T
-- Winch Force = 100 T

(3) Tug is lifting a heavy chain and anchor, AND applying a Bollard pull of 100T
-- Horizontal Force = 100 T
-- Vertical Force = 100 T
-- Winch Force = 141 T

This is the simple diagonal of the triangle of the two force vectors.

It is easy for the indicated winch load to exceed the Bollard pull.

Of course, I'm sitting on my butt with a pencil, not out on the open ocean. What do you experienced skippers think?

 

Don't insist, Stian. I'm afraid you're wrong and Acearch is right. As Terry says the force induced by the mooring chain being pulled from the stern of the vessel has two components (in fact three, but we can forget the transversal one to simplify), one vertical and other horizontal. Propeller pull only 'takes care' of the horizontal one, not the vertical, which is contrarrested by the flotability of the vessel. Forgetting friction, again to simplify, the winch takes care of the vectorial sum of the components, which is in fact the tension in the line. So a 330 mt pull on the winch is perfectly posssible with a 194 mt bollard pull (that's the published bollard pull for BD). Remember also Bourbon Dolphin's had an AH drum able of 400 mt, if I'm not wrong.
Cheers.

(Note: 'mt' for metric tonnes)

 

Redian - of course it was an accident - and your definition of an accident is?

ther has been a lot of people post on this subject who know a lot about the sea and ever situation on it! People are not saying anything against the Master and Crew of the Bourbon Dolphin All we're trying to do is discuss the situation and try to find out what happened and how if possible to prevent it again! with ALL your experience I'm sure over your 25 years you've pulled a few anchors up and down the 'bar', that is what we are doing here, just happens to be a big bar.......think about it!!

 

BRAVO, the world is full of bloody (experts)
as we all know, x the unknown quantity, spurt, drip under pressure,
But well said ,I dont read such drivel, and you just have to try and ignore these people too, hard at times eh)
All the world has utmost respect for the Norwegian Maritime Industry, across the board,

 

Originally Posted by StianM
I gues that could be argued up and down in a 55 page thread all by itself.
If a generator is rated at 200kW and you pull 200kW your running 100%load.
If your running 180tonn bolard pull on a boat reated for 180tonn your at 100% off the capasety off the ship.

StainM, For your info the stall load on the winch on an AHT is normally much much higher than the bollard pull, and a vessel can experience loads that exceed the bollard pull. The Bollard pull is a result of the power that the vessels main engines can output, when breaking an anchor out you can easily exceed the bollard pull.
The figures that follow are from a lower spec vessel than the BD but give you an idea of the different figures dealt with - Bollard pull 83mt, Winch stall 150mt, Brake load is higher than the stall around ~200mt, SWL on Stern roller, pins and forks 300mt, and I have seen a winch stall on this type of vessel, and no excessive heeling or damage occured.

The bollard pull is not a measure of the maximum load that the vessel can handle but a figure that the vessel can work at when towing, look at how a bollard pull test is run, it is measureing straight line pull (towing) when the vessel is secured to a non moving strong point. It is not a safe working load figure.

 

If you runn a bolard pull at 180 tonn and the boat is pulling 180 tonn it's at 100%.

If I lift a weight it might be 100% off the capasety of my arm, but only 20% off the capasety of my feet.

The report say Bourbon Dolphin tok more load than it was alowed too and I gues when they say load they mean load.

 

Another example - the old Laga, 102tonne bollard pull and stability booklet has a 200tonne figure for load on the stern roller when handling anchors, a figure nearly twice the bollard pull. So she was at 100% load when you had 200tonnes load...

 

Let me try to make this simple to understand:

Bollard Pull is the amount of force that a vessel can exert against a stationary object. It is simply the amount of pull that can be developed by the propulsion plant. It simiply does not have anything to do with anchor handling in reality.

Stern Roller rating. This is the Safe Working Load that the stern roller is designed to be able to absorb without damage. This is purely a structural issue and has nothing to do with force exerted by the vessel to the object that the vessel is handling. For example, if a stern roller is rated for 400 tons, that means that the DESIGN SWL is 400 tons; i.e. the roller can take a point load or radial load anywhere on its length of 400 tons without damage.

Tow Pin/Shark Jaw Rating. Similar to stern roller. The rating is the SWL the component can physically take without damage.

Tow Winch Rating. This will usually be given in 2 ratings:

1) Maximum Pulling Force, which is how much the winch will pull against a stationary object. This is a function of the hydraulics and the position of the pulling force on the wrap on the drum. Empty drum pull is more than full drum pull.

2) Maximum Brake Capacity, which is how much the winch brakes can absorb without slipping. This is always quite a bit higher than 1). For example, a 500 ton winch is capable of exerting a pull of 500 tons against an object in the lowest speed range of the winch at bare drum, and will likely have a brake holding rating of 150/200 tons more than the 500 ton pulling capacity.

So now that this is explained, NONE of the above was the reason the BD was lost. As all reports account to, the load that the vessel was seeing from the combined components of the bollard pull [we assume they were still pulling], and the cantenary load of the chain/anchor, and possibly the added component of ballast, all contributed to a load that exceeded the vessel's ability to remain upright when these loads shifted to over the side rather than over the stern.

Still can't figure why they let the load off the tow pin. I don't remember any vessel turning over longitudinally.

 

The vessel I am operating has a winch line pull of approx. 350 tons. And a bollard pull of 140 mt. We have pulled until the winch has stalled out many times working in the deeper water. An example is trying to unseat an anchor. Sometimes it is necessary to pull until the winch stalls, and then increase power to pull the anchor out of the mud. With this example you can see that the forces involved at the anchor by pulling until the winch stalls and then increasing the power to the maximum bollard pull exceed the rated load on the winch and of maximum bollard pull.
-Capt. Chuck

 

Acearch has it right.

The thing I can't understand is how the vessel listed to 90 degrees while the wire was still trapped inside the pins (all the witness testimony had the wire still inside the port outside pin). From what it looks like in the inquiry is that all they were trying to do was shift the wire from the Starboard inside pin to the port outside pin to help the vessel work its way back to Port. When the wire shifted the boat listed 90 degrees. I don't think the side-load happened until the vessel listed and lost power.
Just my $.02
--Chuck