Lessons learned: Up to date forecasts crucial for safe mooring

The incident

A cross-channel ferry was berthed starboard side to with its stern to the linkspan, loading passengers and vehicles ahead of an overnight sailing. There was a fresh breeze of 15-20kts on the starboard quarter, with forecast gusts of around 27kts. Winds during the day had been steady, but gusts above 30kts had been recorded, and some forecasts mentioned squally showers and winds up to Beaufort Gale Force 8 (34-40kts).

Due to the layout of the ferry’s berth, if the winds were consistently less than 25kts it was normal practice, with the master’s agreement, to remove the breast line at half tide or below in the period before sailing. This was because at lower states of tide the line obstructed the passengers’ route to the boarding access tower. This left the vessel moored with two stern lines and a spring line aft, all on self-tensioning winches.

About an hour before departure, as a squall passed through the area, there was a rapid increase in wind speed, with gusts up to 50kts. This bore on the ferry’s starboard quarter. After about a minute, the three after lines all
began to pay out together and the vessel’s stern moved to port, away from the berth.

A section of the passenger gangway, which was secured to the ship about two-thirds of the way from the bow, was drawn out from the embarkation tower until all its weight was on the lightweight lashings to the ship. These quickly parted, and the section of gangway fell into the water. Fortunately, a port employee operating the gangway spotted the danger developing and stopped two passengers who were about to board the ship.

As the stern moved away from the berth, the stern vehicle ramp hit two guardrail posts on the edge of the linkspan, carrying them away. The chief ofcer, present on the vehicle deck, reacted quickly, stopped any
further loading, and ordered that the stern ramp be raised. He also ordered the mooring party to heave on the mooring winches, arresting the swing with the ship’s quarter around 12m from the berth.

After an emergency start of engines and thrusters, the ship’s master manoeuvred the ferry back alongside. The wind had reduced to 10-15kts on the passing of the squall but, as a precaution, the breast line was re-secured. The remaining passengers and vehicles boarded over the stern ramp and the ferry departed an hour later than scheduled to allow more water over the submerged gangway. The gangway section was recovered with the aid of divers the following day.

Lessons learned

1. Self-tensioning winches are designed to work at a constant tension, and will heave in if tension is less than set and pay out if tension is greater. They are designed to keep a ship alongside in varying tidal or draught conditions. Here, in response to a sudden increase in wind speed, and a corresponding increase in forces on the ship and tension in the line, they payed out, operating as designed. If using winches in the self-tension mode, expected conditions for the period alongside must be carefully assessed, and if there is a chance that limits will be exceeded then use of higher tension settings, or holding on the brake with manual monitoring as the tidal height varied, could be considered.
2. While winds at the time of the decision to remove the breast line were within the pre-agreed limits, some forecasts indicated that winds could increase up to force 8 and had mentioned the possibility of squally showers. If considering reducing the security of a ship alongside, then the most up to date forecasts must be sought. If conditions are marginal, mooring lines should be removed only if other mitigations are in place.
3. The sliding gangway section had a minor defect that meant two doors had to be tied to the ship while the gangway was in place. As the ship moved away from the jetty, these ties prevented the gangway operator from disengaging the gangway and led to it falling into the water. Some seemingly minor defects can have major consequences – think carefully before putting of maintenance.