200651 Gas Tanker Off Berth

A coastal gas tanker was a regular caller at a river berth, which is subject to exceptionally large tidal range (up to six metres) and strong tidal currents (up to five knots). While discharging cargo during a recent call, the moorings were inadvertently allowed to lie slack at the time of low water. Soon afterwards, the flood stream that began to flow strongly through the gap between the hull and the wharf caused the tanker to be pushed offshore by more than two metres, requiring emergency stopping of cargo operations as the hose came under tension.

The crew then rushed to man the mooring stations and managed to heave the ship alongside, but only with great effort as the pressure relief valves on the hydraulic systems kept cutting in. Had the current been stronger and had there been significant wind effect on the ship's hull, a very hazardous situation would have rapidly developed, with the possible parting of the cargo hose and mooring lines.

Root cause/contributory factors

1. Failure to tend to moorings as dictated by tidal predictions and good seamanship;
2. Large range of tide and strong tidal stream;
3. Auto-tension mooring winches either not fitted on board or not used correctly.

Other lessons learned

1. At all times, there must be sufficient persons on board to supplement the duty watch for tending the moorings.
2. Where practicable, it may be prudent to include a mooring plan as part of the passage plan, especially in this case, as the vessel regularly called at this river berth.
3. A mooring plan would be subject to minor changes on pilot's or terminal's advice, weather and tidal conditions, but the final mooring configuration must be tended continuously by observing good seamanship. Moorings must never be allowed to become slack under any circumstances, especially when cargo operations are in progress.
4. Mooring winches and lines must be maintained at peak efficiency at all times, both must be of sufficient power/strength for overcoming occasional 'high' loadings safely.
5. Contingency plans for the potential dangers arising from failure or slackening of moorings must be carefully prepared and exercised, involving the shore terminal, agents and harbour authorities, whenever possible, including but not limited to, having tugs available at short notice to push the vessel alongside if need be, or hold the vessel alongside.
6. Ships' staff must be aware of the operational methods and limitations of the mooring equipment including maximum pulling power of winches, the nature, condition and strength of mooring ropes in use, and the effect of tidal currents and wind on the vessel.
7. Position tolerances of vessel with reference to the terminal Chiksan arms must be clearly marked on the shore and be also communicated to all concerned and must be continuously monitored.

    

   Feedback February 2007

   In this report it was erroneously stated under one of the root causes that 'Auto-tension mooring winches either not fitted on board or not used correctly.'
   
   It has been rightly pointed out by one of our members that under ISGOTT recommendtions, such winches, even if fitted, must not be used in auto-tension mode due to the possibility of the vessel being automatically warped up or down the berth and presenting a serious hazard to the cargo hoses and chiksan arms.