MAIB: LNG tanker’s mooring lines were “not fit for purpose”

Zarga alongside at Milford Haven

JUNE 15, 2017 – Five year old mooring lines on the 2010-built LNG tanker Zarga were “not fit for purpose,” says the U.K. Marine Accident Investigaton Branch in its report on a May 2, 2015 incident in which a deck officer suffered severe head injuries when he was struck by a parted HMPE (ultra-high modulus polyethylene) mooring rope during a berthing operation at South Hook LNG terminal, Milford Haven.

The area where the officer was standing was clearly within the snap back zone of the rope, says the MAIB, but had previously been designated as a safe area.

The perception on board was that HMPE ropes did not recoil on failure, and the elasticity introduced by the rope’s tail had not been properly assessed.

The vessel’s mooring lines were not fit for purpose, they did not have the minimum breaking strength specified at build. they were not compatible with the vessel’s mooring deck fittings and the required working load limit was too high.

The predominant failure mode, axial compression fatigue, had not previously been associated with HMPE rope failures.

The rope’s tightly bound jacketed construction increased the likelihood of axial compression fatigue and prevented the crew from inspecting its load bearing core and identifying key discard criteria.

Guidance provided by the rope manufacturers and shipping industry bodies for the selection and use of high modulus synthetic fiber mooring lines was limited and often contradictory.

Safety issues identified by the MAIB were: Thorough snap back zone assessments had not been carried out for Zarga’s mooring lines

Weakness were identified in the command and control prior to and during the mooring operation

Had tugs been recalled to assist in the re-positioning of the vessel the accident might have been avoided

The officer in charge of the forward mooring party got directly involved in a specific task and lost his overall view of the mooring operation

The residual strength of the parted mooring line was below its accepted working load limit

The manufacturer’s recommended safety factors for the rope were not taken in to account by the shipbuilder or vessel operator

The diameter of the vessel’s deck fittings were too small for the HMPE ropes

Mooring line condition monitoring routines on board were ineffective

The rope’s jacketed design made it difficult to identify key discard criteria

Axial compression fatigue had not previously been considered as a likely failure mode or significant cause of strength loss in HMPE rope

Strength testing methodologies, designed for the offshore sector, were inappropriately applied to ships’ mooring ropes

The test methodology used by the rope manufacturer to achieve the required specified MBL for Zarga’s mooring lines was flawed. The realization factor applied was unrealistic and the results were higher than previously or subsequently achieved

Insufficient information was exchanged between the vessel builders and the rope suppliers to ensure the ropes were fit for the purpose

Recommendations

Recommendations have been made to Shell International Trading and Shipping Company Ltd (2017/119 to 122), The Oil Companies International Marine Forum (2017/123 to 125), Bridon International Ltd (the rope manufacturer) (2017/117 to 118) and Eurocord (2017/126) aimed at improving the levels of knowledge among ship owners, managers, builders and crew regarding the complex properties of high modulus synthetic fiber ropes, and the advantages and limitations they present when used on board ships for mooring line applications.

Read the MAIB report HERE