UK MAIB issued an investigation report on the grounding of the semi-submersible rig Transocean Winner, on the Isle of Lewis, following the loss of tow from its tug, due to inclement weather. The report provides a description of what happened and recommendations to prevent similar marine casualties in the future.
Transocean Winner main towing arrangement
Summary
On 8 August 2016, the Marshall Islands registered semi-submersible rig Transocean Winner grounded on the Isle of Lewis, following the loss of tow from the Dutch registered tug ALP Forward. The tug and tow was on passage from Stavanger, Norway to Valletta, Malta, when it encountered severe weather west of the Hebrides. The effect of the wind and waves on Transocean Winner led to the loss of ALP Forward’s ability to control the direction and speed of the tug and tow. After being dragged backwards by the tow for over 24 hours, the tow line, weakened by the repeated sudden loadings, parted and the tug was unable to pick up the emergency towline.
Port and starboard tow stops
Actions Taken
- Revised the Rig Move Planning Checklist to be used as a single document by all parties for the execution of non-self-propelled rig moves with a sign-off section that must be completed prior to commencing a move.
- Updated the Rig Move Plan Template, ensuring trigger, hold points and required actions are defined. This is to be used as a single document by all parties for the execution of non-self-propelled rig moves and includes a Responsibility Table.
- A Transocean approved Rig Move Supervisor holding a Marine Warranty certificate is to be on board the towing vessel of unmanned tows.
- Daily Reports for voyages and extended tows are to include, inter alia, the tow line tension and the percentage of MBL applied.
Conclusions
- The effect of the wind on Transocean Winner led to ALP Forward being incapable of controlling the wind and tow in the severe weather conditions. Without the necessary information, it was not possible for the master to predict the tug’s inability to hold the rig and change his passage plan in time to seek shelter.
- The planning of a passage so close to the coast left little sea room for the tug and tow to drift. When ALP Forward lost control of the tug and tow, it was very likely that Transocean Winner would have grounded even if the tow line had not parted.
- The tow line was in a generally poor condition, there was insufficient catenary in the deployed tow line which led, in the weather conditions, to repeated sudden loadings resulting in the tow line parting. It is quite possible that a new tow line would have also parted under the same circumstances and conditions.
- Improved guidance to tow masters on the importance of maintaining catenary and avoiding shock loading could have helped ALP Forward’s master mitigate the effects the heavy weather had on the tow line.
Transocean Winner aground
Recommendations
- Complies with the guidelines issued by the International Maritime Organization in MSC/Circ.884 of 1998
- Provides those responsible for the safety of the tow with all the necessary information, including tow-specific guidance on:
- The need to consider sea room and lee shores during passage planning
- The provision of an adequate catenary
- The need to report when control of the tow is lost
- The limitations/ functionality of the emergency towing arrangement when in adverse weather
- Provides its vessels’ crews and maintenance staff with comprehensive guidance on the maintenance, inspection and discard of tow lines
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Source: MAIB
