A passenger ferry was attempting to moor on a berth with a strong groundswell in strong winds when, without warning, one of its mooring line bollards was ripped from the deck. The ferry had to be taken out of service for several days to facilitate repairs to its deck plating and a roller fairlead. Fortunately, nobody was injured.
The effects of the groundswell in the port, and the difficulty of berthing in strong winds, were well known to the ferry operator. Between 2015 and 2017 the company recorded 21 instances of mooring line failures, with some causing minor injuries to ships’ crews. The main solution to the problem was to equip the vessel with stronger mooring ropes.
In normal benign conditions the crew used 48mm diameter, 8-strand polypropylene plaited rope to moor the vessel. In more difficult conditions they used larger 64mm diameter ropes. In the worst conditions, a 9m long, 80mm diameter mooring rope was used as a back spring. This 80mm rope had a soft eye spliced at each end. The minimum breaking load (MBL) for the 48mm, 64mm and 80mm ropes was 43t, 75t and 116t respectively. The safe working load (SWL) of the damaged bollard and roller fairlead was 20t and 12t respectively.
Prior to arrival in the port, the master’s mooring plan and decision to use the 64mm mooring lines was explained to the deck crew during a toolbox talk.
However, during the mooring operation, the 80mm rope was used as the back spring. The back spring was passed through one of the vessel’s roller fairleads and its eye splices were looped over bollards on the deck and the quayside.
It was evident that the forces acting on the mooring line - because of the combined effects of the wind and groundswell - did not reach its MBL but significantly exceeded the SWL of the vessel’s deck fittings. This happened because the SWL of the deck fittings had not been properly considered when the size of the mooring line was increased.
1. The problems caused by vessels surging on the quayside in exposed ports are well known and do occasionally lead to mooring lines parting. Masters should assess the suitability of a berth when considering the prevailing weather conditions, review their risk assessments, and establish a clear mooring plan that should include the disposition, size and types of ropes to be used.
2. The parting of a mooring line creates a significant hazard to a ship’s crew; however, snapback paths can be predicted and safe zones identified. The failure of overloaded mooring equipment and the subsequent path of failed components is much less predictable and therefore potentially more lethal.
3. Vessel operators and crew should ensure that mooring line strength does not exceed that of the load limitation of installed mooring equipment such as deck bitts/ bollards, rollers, fairleads and winches. It is recommended that ships’ staff make themselves aware of load limitations of equipment and mooring ropes used before using a rope that deviates from that included in the design of the vessel.
4. The SWLs were not clearly marked on the vessel’s mooring deck equipment. This made it difficult for the crew to understand the potential consequences of using stronger mooring lines.
5. The practice of putting soft eyes over mooring bollards or bitts on both ends of a mooring line is contrary to good seamanship practice as it makes it impossible for crew to slacken or release a taut line safely in an emergency.
Source: MAIB - Safety Digest