In the fifth case of its latest edition of the Safety Digest, the UK MAIB presented an incident that occurred during mooring operations, which did not ended in loss of life, but indicated how important the efficient communication and conscious thinking are when letting go the lines.
An offshore support vessel was moored starboard side to. The mooring arrangements on the stern comprised two spring lines made fast on bitts on the inboard side and two stern lines made fast on bitts on the outboard side. In preparation for the departure, the vessel’s mooring and bridge teams
conducted a tool-box talk.
At the time of departure, the tidal stream was setting onto the vessel’s stern at a rate of about 1.5kts. For letting go, the inboard (starboard) azimuth thruster was set to counteract the tidal stream and the outboard (port) azimuth thruster was set to keep the vessel alongside. The master, chief officer and a harbour pilot were on the bridge. The master and pilot had discussed the manoeuvring aspects of the departure plan, but not the method or
expectations for unmooring. Communication between the bridge and the mooring teams was via hand-held UHF radio. The pilot was talking with the shore linesmen via VHF radio.
The aft mooring team comprised two ABs, one by each set of bitts. The shore linesmen first cast off the spring lines from the quayside bollards. The aft spring lines were recovered on deck by the AB at the starboard bitts. The AB on the port side then slackened both of the stern lines. The shore linesmen then let go the head and stern lines from the quayside and dropped their ends into the water. The lines were too heavy for the AB to recover
simultaneously and, as he heaved in one of the stern lines as fast as he could, the other line was sucked into one of the azimuth thruster suction inlets.
To make matters worse, the line being tended by the AB soon twisted around the line that was fouling the thruster. The AB handling the stern line quickly alerted the bridge to his predicament and asked for both thrusters to be stopped. However, the master realised that this would leave the vessel
without any means of control. The master did not know which of the thrusters was fouled, so he set the pitch of the port azimuth to zero and adjusted the starboard azimuth to keep the vessel alongside, as well as counteracting the tidal stream.
Meanwhile, the AB from the inboard bitts moved to the port side to assist. Even so, the two ABs were unable to hold on to the stern lines, which were pulled out of their hands. At the same time, one of the ABs inadvertently stepped into a bite in one of the lines that quickly tightened around his foot
and then carried him toward a fairlead, as the line ran overboard. The second AB saw what was happening so grabbed the other AB and managed to push his boot off just before it became fast in the fairlead. Fortunately, injury was limited to a bruised foot, and the vessel was re-secured alongside without further incident.