Summary
On 2 March 2015, a deck officer on board the LNG tanker, Zarga, suffered severe head injuries when he was struck by a mooring line that parted during a berthing operation at the South Hook LNG terminal, Milford Haven. The officer, who was in charge of the vessel’s forward mooring party, was airlifted to a specialist head injuries trauma unit for emergency surgery.
Zarga was declared all fast alongside about 40 minutes prior to the accident and the attending tugs were let go. The vessel subsequently moved out of position in the gusty wind conditions during which time the mooring teams were fitting chafing guards to the lines.
As the tugs had already been released, the master instructed the officer in charge (OIC) of the forward mooring party to tension the forward spring lines to warp Zarga back into the correct position. The OIC positioned himself aft of the forward springs’ port-shoulder roller fairlead, and positioned a second crewman forward of him in order to relay his orders to the winch operator. As the winch operator attempted to heave in on the springs, the winch repeatedly stalled and rendered.
Zarga for’d mooring deck: winch and crew positions
After about 10 minutes, one of the spring lines began to rattle and creak, and then suddenly parted. The section of the line between the break and the port-shoulder roller fairlead struck the OIC on his head as it whipped back before going overboard through the fairlead.
Location of OiC found after rope failure
Lessons learned
Zarga forward spring winch (Note: Inboard forward spring line shown was a replacement to the failed rope and was of a different manufacture and construct)
- When connecting synthetic tails to UHMPE, HMPE and wire mooring lines, the energy introduced due to the elasticity of the tails can significantly increase the snap-back hazard.
- Elongation is proportional to the length of tail. Increasing the length of the tail will increase the amount of elongation and hence the amount of energy that can be stored in the line when under load.
- Ship owners/operators should ensure that the type of lines and tails used for mooring lines are suitable for the task and that the dangers of snap-back are fully considered.
- Mooring teams should be aware of the potential for snap-back in all types of mooring line, and the probable areas on the mooring deck that are not safe when lines are under load.
- Mooring lines led around roller pedestals and fairleads can lead to potentially complex snap-back zones. Ship operators and masters should conduct their own risk assessments to ensure potential snap-back zones are identified, and are reviewed at regular intervals.
- Not withstanding the ongoing investigation into the nature of the failure of Zarga’s spring line, where doubt exists on the continued use of a mooring line, the vessel operator should obtain guidance from the rope manufacturer on the conduct of detailed line inspections
Location of rope failure
Safety issues
- 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 ship builder 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 Bridon to achieve the required specified MBL for Zarga’s mooring lines was flawed. The realisation 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
Failed rope on pallet for delivery to MAIB
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 fibre ropes, and the advantages and limitations they present when used on board ships for mooring line applications.
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Source: UK MAIB
