Poor condition of a towing line, bad weather and an insufficient passage plan were reasons why a semi-submersible drilling rig struck rocks in western Scotland in August 2016. These were factors in the grounding of drilling rig Transocean Winner on the Isle of Lewis while being towed by Dutch registered tug ALP Forward.
The UK Marine Accident Investigation Branch (MAIB) recommended that tug operator ALP Maritime Services should review its procedures and towing manuals following the accident. The rig was being towed from Stavanger, Norway to Valletta, Malta by ALP Forward, when it encountered severe weather west of the Hebrides on 8 August 2016.
MAIB investigated the accident and published the report on 6 September 2017. Its key findings were that high winds were a factor in ALP Forward being incapable of controlling the tow, and that the master did not have the necessary information to predict the tug’s inability to hold the rig and change his passage plan in time to seek shelter.
Another finding from the investigation was that the planned passage was too close to the coast, so it left too little sea room for the tug and tow to drift and recover.
“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,” MAIB said in a summary.
MAIB said the tow line between Transocean Winner and ALP Forward “was in a generally poor condition” and that there was “insufficient catenary in the deployed tow line”. This meant that, in the weather conditions, repeated sudden loadings resulted in the tow line parting.
However, MAIB did admit that a new tow line may also have parted under the same circumstances and conditions.
After weeks of remaining lodged on the Isle of Lewis, Transocean Winner was eventually refloated and towed to Malta.
In November 2016, ALP Maritime Services and Transocean were questioned by the UK Government about the grounding of a rig in Scotland. The grounding of the rig prompted renewed calls for the reinstatement of a second emergency towing vessel in the west coast of Scotland.
The MAIB report into the August 2016 accident can be viewed here.