BANK REJECTION

June 27th, 2012 by JCB
Posted in Incidents & Investigations, Technical and Training | No Comments »

Photos : MAIB

It would appear that my Royston Grange article in the October 2011 issue was published just too late to avoid an almost identical collision scenario which features in the latest MAIB digest! Fortunately on this occasion there was no loss of life but the following edited extract from the MAIB report highlights the need for caution when navigating in narrow channels.          JCB

A 10,000 tonne container vessel, with a pilot embarked, collided with another vessel which was proceeding in the opposite direction of a narrow channel. Both vessels suffered extensive damage and were out of service for a considerable period while costly repairs were undertaken.

Prior to the collision, the container vessel had increased speed to overtake a small barge as she entered a long, narrower channel. The overtaking manoeuvre resulted in her being on the extreme starboard side of the channel, close to the bank. A short time later the vessel then took a sudden and uncontrollable sheer to port into the path of a vessel proceeding in the opposite direction.

Analysis of information obtained from the container vessel’s VDR showed that she was influenced by bank effect and squat prior to the collision. The vessel’s speed was excessive, and she was closer to the bank and in less water than the bridge team had planned for. In shallow water, with reduced under keel clearance, the vessel’s pivot point would have moved aft, reducing her steering lever. Close to the edge of the bank the large forces associated with the high pressure area around her bow and the low pressure area around her stern caused the sudden sheer to port which the helmsman was unable to correct before the collision occurred.

Fundamental to incident was the decision to overtake the barge at the entrance of the smaller channel. This decision to overtake was taken to avoid following the slower barge along a channel where overtaking would have been difficult. However, the decision was made without sufficient communication between the bridge team or consideration of the consequences of the manoeuvre.

The Lessons

1. The cause and effects of interaction should be recognised and taken into account. Speed is critical, since the magnitude of forces created by both bank effect and squat increases with the square of the vessel’s speed through the water.

2. The requirements of planning and executing a safe navigational passage must be clearly and fully understood and implemented by all bridge officers. SOLAS Chapter V clearly defines the requirements for the planning and conduct of a safe navigational passage and the key elements of these are:

Appraising, Planning, Executing and Monitoring

When a pilot supplements the bridge team, these requirements do not change; if anything, the ship’s permanent team should be even more vigilant when monitoring the execution of the mutually agreed passage plan.