Inadequate passage planning causes hull damage

In its Safety Digest, UK MAIB describes an incident of hull damage of a ro-ro ferry, highlighting the importance of having a passage planning, even when crews are familiar with a route, as well as of using correctly ECDIS as an aid to navigation.

The incident

During its normal daily service, the ferry was approaching harbour at its full sea speed of about 20kts via a particularly narrow channel. It was mid-afternoon, the weather was fine, sea calm, visibility good and it was low water on a spring tide. The unusual tidal conditions in the area meant that there was about 3kts of tidal stream setting the ship off course to port even though it was low water.

The master was very familiar with the route and was using the visual leading transit marks for the harbour approach as the primary means of positional awareness. The chief officer was also on the bridge as well as the OOW and a helmsman, who was steering by hand. The ship was fitted with an ECDIS system and the crew were certified for ‘paperless’ navigation. The ECDIS safety contour had not been adjusted for the local conditions and, although the cross-track distance (XTD) settings were appropriate, the audible alarm had been switched off.

As the ferry proceeded down the channel, the master observed visually that it was slightly to port of the intended track and made a succession of 2° heading alterations to starboard; however, these adjustments were insufficient to regain track and the ferry raked over a charted, rocky pinnacle. A heavy, shuddering vibration was felt throughout the ship as the outer hull was damaged along most of its length.

The hull was breached in several places but the subsequent flooding was contained in the double-bottom void spaces. The master thought that the vibration had been the result of the vessel’s propeller or rudder picking up some fishing pots, and instructed the OOW to look astern. Nothing was seen. No alarms sounded on the bridge or in the engine control room and the ship responded normally to wheel and engine orders as the propellers and rudders had not been struck.

The crew took no immediate action to identify or assess for damage and the vessel proceeded to its berth as planned. A subsequent, pre-planned dive survey soon found the hull damage.

Lessons learned

Passage planning is critical for every voyage even when the bridge team are extremely familiar with the route. In this case, neither the very low tide nor the effect of ‘squat’ when at high speed in shallow water had been taken into account. Had either of these factors been properly considered, it would have been apparent that it was going to be unsafe to attempt a high speed passage through the narrow channel. The master, chief officer or OOW could have completed accurate navigational calculations prior to the passage; had they done so, the danger would have been apparent. In addition, the master’s alterations of course were insufficient to regain track given the strength of the tidal stream.

Bridge teamwork is vital. Because the master had not verbalised his plan beforehand and there had been no briefing, there was no shared appreciation of the plan among the officers on the bridge. This meant that the ability of the chief officer and the OOW to assist the master was limited as they were unaware of his intentions. A shared ‘mental model’ of the plan and a strong team ethic will help underpin confident, safe pilotage.

Even in pilotage waters when visual references are the primary means of positional awareness, ECDIS still has a role to play as an aid to navigation. In this case, the ECDIS was effectively being ignored; it was not set up correctly for the local conditions and the audible alarm was
off. Had the safety contour been adjusted correctly, it would have been apparent that the channel was not safely navigable at low water. Equally, when the vessel passed outside the XTD, the alarm could have alerted the crew to danger. Under all conditions of navigation, including pilotage, it is important to ensure that ECDIS is correctly used.

Despite a shuddering vibration, the ship was not immediately checked for damage. This is understandable as there were no alarms, the ship was responding normally and the command priority was to enter harbour safely. Nevertheless, the crew should have taken immediate action to check for damage. Had this happened, the void space flooding would probably have been detected sooner.