Accident Investigation Report 19/2017
MAIB drone footage
At 0652 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.
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.
Video extract from TTI rope tests
ALP Maritime Services has been recommended (2017/135) to review its procedures with regard to the production of towing manuals to ensure that the guidance provided in them:
- 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
Published 7 September 2017