200850 Ramp door near miss

During her maiden voyage, the CO of a new ro-ro ship was preparing to set the stern quarter ramp door for cargo operations. After confirming from crew members located at several internal decks that all the cleats were fully open, he operated the hydraulic winch control at minimum speed to gently open and lower the ramp door.

Instead of a controlled, slow, movement, the winch started to pay out at a very high speed, causing the 80-tonne ramp door to accelerate in a free fall towards the wharf. Moving the remote control lever to stop position had no effect as the winch continued to pay out freely, and the mechanical brake was unable to check the momentum. Responding to the shouts overheard on the portable VHF radios the master, who was busy with arrival formalities, ordered the CO on the VHF to move the winch control lever to ‘full hoist’ position, while he rushed towards the after deck.

On moving the winch control lever to ‘full hoist’, the winch responded by gradually slowing down in its rotation, stopped briefly and then slowly began to hoist the ramp inwards. The location of the operating console was about 20 metres from the winch and, with the CO stationed there, the master, who was at the winch, observed that there appeared to be a mismatch between the remote control lever and the actuator control on the winch. As soon as the ramp door reached the closed position, the master ordered all the securing cleats to be locked and the winch’s emergency stop button was activated.

Result of investigations
Foreign matter (pieces of rag and chipped weld bead) in hydraulic oil in the winch control circuit was found lodged in winch’s lowering actuator. This kept keeping the valve stuck open, regardless of the control lever’s position.

Lessons learnt
Hydraulic systems must be kept scrupulously clean and lines that are open during installation and/or maintenance must be adequately covered to prevent entry of foreign matter.
Before ramp door operations, with the ramp secured and the winch drive out of gear if possible, the movement of winch actuators must be confirmed to be in synchronisation with the remote control lever.
Magnetic and barrier filters must be regularly opened up and cleaned or renewed as per maker’s instructions.