Mooring Line in Tunnel Thruster

While carrying out a mooring operation in port, the vessel was using increased bow thruster power to maintain position against an astern wind of approximately 13 knots and the low-friction characteristics of the quay fenders. Following the securing of the aft moorings, the forward mooring party sent a spring line ashore using a heaving line. A second heaving line and bow line were connected in a "daisy-chain" arrangement to facilitate handling by shore linesmen.

The berth arrangement required linesmen to receive the heaving line and then move it along the shoreline to a dolphin. The shore route consisted of uneven, rocky terrain. Communication between the vessel and shore personnel was limited to verbal and visual signals.

As the bow line was being paid out, a crew member observed the attached heaving line moving towards the bow thruster area. The exact reason the line became uncontrolled could not be determined; it may have been inadvertently released, become detached, or slipped from the control of shore personnel. The heaving line entered the water and was subsequently drawn into the operating bow thruster by suction forces. The attached mooring rope was then also pulled towards the thruster.

The bridge was immediately informed, and bow thruster power was reduced. However, Thruster No. 1 tripped and shut down after ingesting the line. The vessel began to move off the berth but was safely brought back alongside using Thruster No. 2, and an additional bow line. Once safely moored, all thrusters were shut down, and it was confirmed that a rope had become lodged in Thruster No. 1. 

Divers were mobilised and successfully removed the rope by hand. Inspection and operational testing identified no damage to the thruster or propeller, and the unit was returned to service.

To view this MSF alert in full, click the 'Download Alert' button.