On 12 April 2007, the Anchor Handling Tug Supply (AHTS) vessel ‘Bourbon Dolphin’ was engaged in anchor handling operations for the semi-submersible drilling rig ‘Transocean Rather’ in the Rosebank oilfield to the west of the Shetland Islands.
The vessel was turned so that the chain on the stern was moved clear of the inner starboard tow pin against which it was resting, which was then retracted into the deck. The chain then moved sideways rapidly across the stern a distance of 2.7m until it was hard up against the port outer tow pin, the inner port tow pin having been retracted into the deck previously.
The vessel subsequently listed dramatically up to 30 degrees to port, which lasted about 15 seconds, before the vessel righted herself. At this time, the vessel briefly blacked out and the starboard engines stopped.
The vessel then listed over to port a second time and then rapidly capsized at 17.08.
While preparations for towing were underway, the ship sank three days after the incident in the Chevron field, 85 miles west of the Shetland coast.
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A total of 7 crew members were rescued, but another eight did not make it. Among the deceased were the Master and his 14-year-old son, who was visiting the ship.
The official investigation report identified several safety issues leading to the casualty:
-Design and Stability:
- The ship was found to have a lightship displacement of 3202t, while she was originally designed to be 2810t, this was reportedly due to poor weight control of component parts during her construction.
- Although the vessel was only in service a short time before she was lost, operational experience found that the vessel had to operate with large quantities of bunker fuel onboard so as to maintain adequate stability, and had previously experienced a large unexpected angle of heel whilst engaged in a towing operation. All precursors to the fact that the stability of the vessel was an area of concern.
- The vessel did not comply with all the load line stability requirements.
- The instructions for Master in the Stability Book were found to generic and did not contain any instructions specific to the vessel, particularly the fact that the roll reduction tank should be empty during anchor handling operations.
-Rig Move Planning
- There was lack of Hazard Identification and Risk Analysis prior to operations commencing,
- The rig move procedure also lacked in that weather limitations were not specified in line with the requirements of interested parties,
- No pre-rig move meeting was held prior to the operation where all interested parties were represented.
The Master onboard… had stated that his vessel was not suitable for the operation due to the fact that a bollard pull of 194t had been calculated as being necessary to break out the anchors from the seabed, whereas the capacity of the vessel was only 180t. The Master therefore subsequently believed he would only be used as an assisting vessel engaged in grapnel work.
- Although the vessel was rated at 180t bollard pull, excessive use of the thrusters would have put demands on the shaft generators that would have reduced the power available to the main propellers, possibly dropping the available bollard pull down to 125t.
The bollard pull requirement for the weight of the mooring system alone in the rig move procedure was 160t. This was a great deal higher than the bollard pull available to the ‘Bourbon Dolphin’ as she battled to get the vessel back to the track using her thrusters and propellers. Therefore the vessel was chartered when at best her available bollard pull could have been considered as borderline for the task of anchor handling for this particular operation.
- It was found that the winch capacity specified was too low for the dynamic forces which could have been expected during the operation.
- The Captain was only given 90 minutes to familiarize himself. Neither the Company nor the operator ensured that sufficient time was available for the changeover of the crew.
- The vessel was small, compact and uniting several requirements such as bollard pull, anchor handling demands, powerful winches, big drums and equipment for handling chain.
- The Company was unfamiliar with the design of the vessel and should have carried out more thorough critical assessments.
- The Company had not noticed the fact that the vessel had experienced an unexpected stability incident two months after delivery.
- The vessel did not have sufficient stability to handle lateral forces and the winch’s pulling-power was over dimensioned in relation to what the vessel could withstand regarding stability.
- The Company itself had not researched whether the vessel was suitable for the operation it was to carry out.
The ISM Code demands procedures for key operations. Despite anchor handling being the main function there was no vessel-specific anchor handling procedure. The Company did not follow the ISM Code requirements that all risks are identified and the company did not make sufficient requirements for the crew’s qualifications for demanding operations. The procedures demanded the use of two vessels operating in close proximity.
In January 2009, the owner was fined €530,000 after a Norwegian government Commission of Inquiry raised doubts about the ability of both the vessel and its crew to handle large anchors in such deep water. Norway's national prosecutor also stood at the fact that the new captain had not been given enough time to learn the ship, as he only had 90 minutes to take over.
The incident highlighted necessity of the inclusion in a vessels stability book of anchor handling specific stability conditions and situations that prove the stability of the vessel is adequate. This information should be vessel-specific rather than the standardized generic information which is provided to different vessel types.
Issues regarding inadequate personnel training, both formal and simulation, in anchor handling operations were also raised.
It also raised concerns regarding the length of time for the handover of personnel, which should be specified by operators in their Safety Management System, especially when crew are joining a vessel they are not familiar with, so as to ensure that they are sufficiently informed about the vessel and its characteristics prior to the departure of the relieved crew member.
Additionally, the report recommended that planning and the rig move plan should be improved, with the plan being operation specific, provided to all parties well in advance of the operation and an onshore meeting help of all critical personnel.
Risk assessments must also be conducted for the overall operation and also for the operations to be performed on each vessel.
Finally, the report underlined that risk assessments used onboard AHTS vessels for these operations mostly focus on the dangers of the anchor handling operation from the perspective of what is to be done on the working deck, while little attention is paid to the dangers affecting the actual vessel. So it was recommended that this would be included in pro-forma risk assessments used onboard prior to operations commencing.
Explore more in the official report: