200634 Mooring in strong tidal area

One of our tankers was in the process of discharging recently on a river berth where it was known that there was a large rise and fall of tide (up to six metres) with associated strong currents (in the region of five knots). On the change of tide the vessel was pushed off the berth by the flood tide.

The master and crew of the vessel were aware of this phenomenon. The vessel was a regular caller at the port and the nature of the berth was known to all concerned – even to the extent that additional shore moorings were taken by the vessel as a regular process in the mooring operation.

It appears there was an acceptance, by both the terminal and the vessel, of the fact that the vessel would normally lay slightly off berth under certain conditions of the tide. However since on this occasion the vessel was up to two metres off the berth, this situation was unacceptable to the terminal and the vessel was instructed to stop discharge. Regrettably this was the first intimation of a problem to the master and deck officers, who were either unaware of the situation or unconcerned. As a consequence the vessel took no proactive measures to remedy the situation until it had developed to a dangerous and unacceptable level.

Remedial action was taken onboard to bring the vessel back alongside the berth but regrettably the vessel did not take into account the limitations of the winch, which was limited to 14 tons' pulling power (governed by the safety relief valve setting on the hydraulic system). On this occasion it proved sufficient to pull the vessel back alongside the berth. Had the current been stronger and there had been significant wind effect on the ship's hull this may not have been the case: the vessel may well have been pushed further from the berth and even broken free from her moorings. The consequences would have been further aggravated, as the cargo arm was not disconnected at any time in this incident.

Recommendations

• Ensure that proper planning is in place to ensure that moorings are properly tended at all times;
• Take into account local conditions on the berth that may affect the safe mooring at all stages of tide and cargo operations;
• Make contingency plans for the potential dangers associated with berths acknowledged to be prone to difficulties associated with moorings, including but not limited to having tugs available at short notice to push the vessel alongside if needs be, or hold the vessel alongside throughout the whole operation;
• Ensure that ships' staff are aware of the limitations of the mooring equipment including maximum pulling power of winches and the effect of tidal currents and wind on the vessel as she lays alongside a berth;
• Ensure there are sufficient persons onboard to supplement the duty watch should it be necessary to significantly adjust the ship's moorings;
• Take account of the nature of the mooring ropes being used for the operation, elasticity breaking strain and general condition;
• If there is an accepted practice of the port that the vessel may lay off the berth while loading or discharging, limits should be agreed between the vessel and the terminal, and an agreed course of action be drawn up if these limits are exceeded, or it becomes apparent they may be exceeded.

Conclusion

It would seem there was a lack of awareness on the part of the vessel about the acceptable limits for the berth concerned; the likely effects of the tidal currents on the berth; the danger associated by being so far off the berth; and the likelihood that the vessel may have broken free from her moorings had the ropes being used to heave the vessel back alongside 'backed up' due to the power limit settings on the mooring winch hydraulics.