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A 20,000 gross tonnage cargo ship was unberthing with the aid of tugs. The tugs were each using a ship’s line for towing. Each line passed through a panama fairlead and was secured to a set of mooring bitts.

As one of the tugs began to increase its pull, the applied load exceeded the SWL of the ship’s structural mooring equipment. As a result, the mooring bitts failed along with the supporting structure for the panama fairlead. Consequential damage included buckled ship- side guardrails and bulwark.

The ship’s crew noted that the SWL of the fairlead was 8 tonnes (t). They therefore
took local action to highlight all mooring equipment rated at 8t, and instructed that this equipment was not to be used for towing, and included this information in pre-departure/ arrival toolbox talks.

Several months later, the same ship was arriving in a different port, again using tugs. A tug was secured with a ship’s line to a
 32t SWL set of mooring bitts with the line running through a ship-side fairlead. As the tug moved to reposition itself, additional load came onto the towing line, resulting in failure of the mooring bitts.

Following the incident, the vessel successfully moored alongside. About 12 hours later the prevailing wind and swell in the harbour caused the ship to surge along the berth and the mooring lines to tighten on another set of bitts (rated at 15t), resulting in deformation and failure of the structure.

The ship was built in 1977 and retained the original mooring equipment, which had been maintained to Flag State and Class requirements throughout its life. The mooring lines had been changed through life as technology improved the characteristics of available products. The lines in use at the time of these incidents were high modulus polyethylene (HMPE).

The manufacturer advertised this particular rope type as: ‘a lightweight, high-strength, floating rope that can grip on a capstan or H-bitt. The patented technology provides superior abrasion and cut resistance, but with a higher coefficient of friction than other high modulus polyethylene ropes.’

Source: MAIB - Safety Digest