The UK Marine Accident Investigation Branch (MAIB) has published the result of its investigation into the failure of a mooring line on board the LNG carrier Zarga on
March 2nd 2015, which resulted in a deck officer suffering serious injury. At 19:08 on the date of the incident the officer-in-charge of the forward mooring party was struck by a mooring rope that parted during a berthing operation at the South Hook LNG terminal, Milford Haven. The high modulus polyethylene mooring rope had been deployed as a spring line and was being used to warp the vessel along the berth. There were strong gusting winds at the time.
The injury occurred because the victim was standing in the snap-back zone of the spring line when it parted. Because a thorough snap-back assessment had not been carried out by the vessel operator, the area where he was standing was designated as a safe area; there was also a perception that high modulus polyethylene ropes did not recoil on failure.
The spring line parted due to tensile overload, even though the load being applied to the line at the time was less than a quarter of its specified minimum breaking load. The predominant cause of the rope’s loss of strength was found to be axial compression fatigue.
MAIB said that factors that contributed to this included high cyclic loading at exposed ports, repeated and prolonged bending around deck fairleads and radial compression exerted on the load bearing core by the rope’s tightly bound jacket.
Although the Zarga’s mooring lines had been subjected to regular visual inspections by the ship’s crew and the rope manufacturer’s representatives, their condition had always been assessed to be good. MAIB said that the ropes’ jacketed design prevented the identification of key discard criteria such as broken yarns and fused fibres. In addition, other high modulus synthetic fibre rope condition degradation phenomena, such as creep, could not readily be assessed without physically dissecting the rope.
The MAIB investigation concluded that:
1) the arrangement of Zarga’s mooring decks contributed significantly to the rope’s loss of strength and the officer being injured;
2) the mooring lines used on board Zarga and similar vessels in the same feet were not suitable for the application;
3) the primary influences on rope degradation and failure modes were not fully understood by the user, or appreciated by the shipping industry.
As a result of its initial findings, the Marine Accident Investigation Branch issued two Safety Bulletins: the first relating to the snap-back injury and the second to the difficulties of inspecting jacketed ropes.
The vessel operator, Flag State, rope manufacturer and industry bodies had all taken action to improve awareness of the issues identified in this report, MAIB said. The Oil Companies International Marine Forum had undertaken to consider “carefully” the findings of this report during the revision of its Mooring Equipment Guidelines.
Recommendations have been made to Shell International Trading and Shipping Company Ltd, The Oil Companies International Marine Forum, Bridon International Ltd and Eurocord. https://assets.publishing.service.gov.uk/media/59400114e5274a5e4e000239/MAIBInvReport13_2017.pdf
Also, from July 2015: https://www.gov.uk/maib-reports/safety-warning-issued-after-mooring-line-failure-on-board-lng-tanker-zarga-resulted-in-serious-injury-to-a-deck-officer