MAIB reveals findings after Zarga LNG carrier’s mooring line failure
The UK’s Marine Accident Investigation Branch informed that on 2 March, 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.
Following the accident, MAIB commissioned a series of tests and trials designed to measure the elongation and snap-back characteristics of the mooring lines used on board the Nakilat owned Q-Max carrier Zarga. A Safety Bulletin was issued to highlight urgent safety lessons that have arisen in the early stages of its investigation of the incident.
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 and the officer in charge was instructed to tension the spring lines to move the vessel back into position. After several failed attempts the spring line parted and injured the OIC, stands in the accident report.
The 5-year old mooring lines fitted to the vessel were 44mm diameter sheathed ultra-high modulus polyethylene with a length of 275m and a minimum breaking load when new of 137t. On board Zarga, 11m tails were originally fitted to reduce peak dynamic loading, but these were replaced with 22m tails after peak dynamic loads were experienced that had led to a series of line failures. However, the 22m tails had much greater elasticity and this, and the routeing of the line, introduced a significant snap-back hazard to the outer section of the failed UHMPE mooring line, MAIB said in its bulletin.
The trials revealed that when sections of the UHMPE rope were loaded to the point of failure the average maximum elongation was about 2% and minimal snap-back was observed. When the trial was repeated with the Euroflex tail attached the elongation was significantly increased. Similar to the accident, it was the UHMPE section of the line that parted, and the failed end that was attached to the tail snapped back over 15m in less than 1 second.
MAIB found that among other things mooring teams should be aware of the potential for snap-back in all types of mooring lines and that, 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.
LNG World News Staff; Image: MAIB