SNAP BACK ZONE

 SNAP BACK ZONE 

LOSS PREVENTION ARTICLE








A snap-back is the sudden recoil of a mooring line as a result of its failure under tension. A snap-back zone on a mooring deck is the space where it is anticipated that the failed mooring line could recoil with great velocity, possibly resulting in injury or even death to crew present within this zone.

Until recently, this guidance recommended the marking of snap-back zones on the mooring deck around the critical points such as the warping drum, roller fairleads and pedestal rollers. The aim of these markings was to warn the seafarers to avoid standing in these zones when mooring lines were under tension.

However, recent studies have shown that the nature of snap-backs is more complex than initially perceived. This is due to various factors such as:

• Mooring configurations.
• The nature of the mooring line used with regard to elasticity.
• Breaking strength which may influence the trajectory of a parted mooring line.

Hence the marking of snap-back zones on the deck, although convenient and simple, does not reflect the actual complex snap-back zone and may lead the seafarer into a false sense of security that they are safe as long as they aren’t standing in the highlighted area.

The latest version of the COSWP and MEG4 dissuades the marking of snap-back zones on the deck.

It recommends that the entire mooring deck should be considered as a potential snap-back zone and clear visible signage must be displayed to warn crew. It is also recommended that a bird’s eye view of the mooring deck is produced to identify potentially dangerous areas. The diagram below is an extract from the COSWP and gives an example of how the snap-back zone may be depicted on a mooring plan.


Image: The diagram shows the potential areas of danger (snap-back zone) when the spring line parts at the spring line fairlead.


Most mooring line accidents occur as the result of unexpected and violent mooring line movement. Lines can move for a number of reasons such as becoming snagged and snapping free, being mishandled on the drum or strong point, or simply breaking. Snagging conditions can develop due to surface defects on the dock or ship, or by simply having the mooring line in an unsafe location, to begin with.

It is essential that sufficient personnel are detailed to attend the mooring operation and that the activities to be undertaken are adequately explained and supervised by a deck officer. Personnel not involved in the mooring operation should be kept well clear of the mooring decks. In the event of an unusual or non-standard mooring operation, it is recommended that a new risk assessment be completed before the operation commences as they will potentially have associated hazards not covered within the risk assessment done for a standard mooring operation.

 
Case study of snap back zone:

This animated video depicts a mooring accident that occurred when a bulk carrier was discharging cargo alongside a mineral terminal. While repositioning the vessel astern the terminal, using only mooring lines and with the engine on stand-by, the master became concerned the vessel was developing excessive sternway.



On the poop deck, an able seaman tightened up the back spring winch brake and as the strain came on the rope, it parted with one end of the rope snapping back, violently striking the second officer. The injured seaman suffered broken ribs and serious internal injuries.


Recommendations of OCIMF and lessons learnt

The following recommendations and lessons learnt include those contained in the MAIB’s interim Safety Alert relating to snap-back; these should be widely promoted and shared:


1.      In the event of an unusual or non-standard mooring operation, it is recommended that a new risk assessment be completed before the operation commences as they will potentially have associated hazards not covered within the risk assessment done for a standard mooring operation.

2.      .*Maintain mooring equipment and ropes

3.      *Overtightening the winch brakes is dangerous

4.      *The whole mooring deck is a snap back zone

• When connecting synthetic tails to HMSF and wire mooring lines, the energy introduced because of the elasticity of the tails can significantly increase the snapback hazard.

• Elongation is proportional to the length of the tail. The fitting of longer synthetic tails, e.g. 22m tails, proportionally increases the stored energy and the amount of snap-back that can be expected.

• Elongation of the tail will increase the amount of stored energy in the tail when it is under load. Should a mooring line fitted with a synthetic tail fail, it should be expected that the snap-back will affect the entire length of the mooring line, irrespective of the type of mooring line used. It is important that ship’s personnel are aware of the increased snap-back hazard introduced by the fitting of synthetic tails.

• Ship owners/operators should ensure that the type of mooring lines and tails used for mooring are suitable for the task and that the dangers of snap-back are fully analyzed, taking account the mooring configuration employed. Mooring plans should depict the identified snap-back hazardous zones.

• Mooring lines led around roller pedestals and fairleads have the potential to create complex snap-back zones. Ship operators and masters should conduct their own risk assessments to ensure potential snap-back zones are identified and reviewed for every mooring configuration.

• Prior to any mooring operation, a pre-mooring tool box talk should be held to ensure that mooring teams are aware of the potential for snap-back in the proposed mooring configuration, and the probable areas of the mooring deck that are not safe when mooring lines are under load.

• For new-build ships, full consideration should be given to this revised understanding of snap-back and the ergonomics involved with positioning of both mooring equipment and mooring team to minimize the dangers to personnel. Issues such as the provision of clear line of sight between the winch operator, personnel signaling and personnel in supervisory oversight of the mooring operations should be considered.


To know more about Mooring and SDMBL please read the below article.

https://capt-philip.blogspot.com/2023/09/mooring-update-is-new-in-ship-mooring.html




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