The Hazards of Mooring Line Snap-Back

Although well documented in accident reports and publications such as the Code of Safe Working Practices for Merchant Seamen and OCIMF’s Mooring Equipment Guidelines and Effective Mooring guides, numerous incidents are still occurring where crew members are injured as a result of the snap-back of mooring lines which have parted under load.

A lack of awareness and a failure to properly assess potentially dangerous snap-back zones during the planning of mooring operations results in crew members being positioned in dangerous areas. In the event of the mooring line parting this poor positioning can result in serious or fatal injury.

A critical factor in the planning and assessment of the risks associated with a mooring operation, is understanding the properties of the mooring lines in use. Consideration must also be given to the effect any tail will have on the characteristics of the mooring rope. This is particularly relevant when fitting synthetic tails to high modulus synthetic fibre (HMSF) and wire mooring lines, both of which have less elasticity than synthetic ropes.

The increased elasticity and the increased elongation of synthetic ropes will increase the amount of energy stored in the tail when under load. The longer the tail the greater its potential elongation and so the greater the energy stored in the line.   Should the mooring line fail, then the entire length of the mooring line could be expected to snap-back as a result of the increase in stored energy. If the line has been directed around rollers, then it is likely that complex snap-back zones will be created.

The potential for complex snap-back zones being created, and the potential for the elastic properties of the mooring line to be significantly changed, highlights the importance of properly planning mooring operations, ensuring all personnel involved have identified potential snap-back zones and are positioned clear of these areas throughout the mooring operations.

OCIMF recently conducted an investigation in to a serious incident resulting from a mooring line failure on board a large LNG carrier and published their findings entitled – The Hazards of Snap-Back www.ocimf.org/media/57482/The-Hazards-of-Snap-back-Initial-learnings-from-a-serious-incident-of-mooring-line-failure.pdf in September 2015.

Further guidance on mooring operations can be found in North’s Loss Prevention Briefing – ‘Mooring Operations’ www.nepia.com/lp-briefings and in our ‘Mooring Operations’ Hot-Spot www.nepia.com/Hot-Spots