MAIB PUBLISHES REPORT ON THE INVESTIGATION OF THE PARTING OF THE MOORING LINE BETWEEN THE TETNEY BUOY AND THE NORTH SEA SHUTTLE TANKER RANGDRID

8 Feb 2002 11:11 AM

The Marine Accident Investigation Branch (MAIB) today published its report on the investigation of the parting of the mooring line between the Tetney buoy and the North Sea shuttle tanker Randgrid, on the 20 December 2000, resulting in the discharge of 12 tonnes of crude oil into the Humber Estuary.

SYNOPSIS

This incident was reported to the MAIB by the vessel''s owner, Conoco Shipping, on 20 December 2000.

Randgrid arrived in the area of the Tetney monobuoy at 0055 on 20 December 2000, where she was met by the service boat Spurn Haven, and the tug Lady Debbie. Two Conoco berthing masters and two SGS cargo inspectors boarded while Lady Debbie was secured astern. With the pilot on board, and in south-east winds of thirty knots and seas of 1.5 to 2.0m, the vessel proceeded to her berth using her dynamic positioning system (DPS) during the final stages of approach to the buoy. Despite the difficult working conditions, berthing was carried out safely, and Randgrid was secured at 0135. Both berthing masters confirmed that the chain stopper was fully closed on to the chain before arranging for the messenger rope to be slacked back as usual.

The chief officer discussed the discharge with the cargo surveyors and went to supervise the pump and line set-up. The first discharge hose was connected at 0210, and discharge started at 0245 with a line pressure of eleven bar. A small leak caused a delay, but by 0350 the discharge pressure was back to eleven bar. At that time the bridge berthing master became concerned about the vessel''s movements under wind and tide, so arranged for the steering control to be changed from DP to manual. The chain stopper was also checked. Between about 0415 and 0430, the chief officer went to the bridge and shut down the hydraulic pumps controlling the power systems forward. Before going to his cabin, he told the duty able seaman to check the mooring at regular intervals. This was carried out between 0500 and 0730; the mooring being confirmed secure. By 0715, with the flood tide due, the berthing master arranged for the tug astern to maintain a slow astern speed.

At 0753, the aft discharge hose pulled away. The duty cargo officer stopped the pumps and started to close the valves. Shortly afterwards, the forward hoses broke away. On the bridge, the berthing master became aware that something was wrong with the mooring, looked up, and saw the first of the hoses pulling free. Tetney Terminal was informed, and the standard terminal emergency arrangements were implemented. The astern tug was brought into play while Randgrid''s main engines were started, and by 0812 the vessel was able to manoeuvre under her own power. Randgrid then went to an anchorage while terminal vessels contained and dealt with the oil spillage.

An investigation revealed that both spool pieces and flanges were damaged on the hoses, with slight deformation and cracking in weld flanges. The chain stopper was found in the closed position, but the chafing chain was missing. Subsequently, it was established that the chafing chain had been released from the chain stopper because the chain stopper controls had been operated accidentally. The pickup rope held the vessel until the lashing, securing the chafing chain to the pickup rope, failed at about 0750.

No staff were injured, but an estimated oil spill of about 12 tonnes occurred.

This report recommends that the owner changes the design of the chain stopper control and alarm system, as well as bridge management procedures.

RECOMMENDATIONS

Conoco Shipping Norge, with respect to Randgrid, is recommended to:

1. Review the current bridge control system of the chain stopper whereby a multi-functional screen uses the same function key to operate two differing, but critically interrelated, control actions. The object of the review is to ensure that there is positive separation between the two systems such that the likelihood of a similar error is either removed or significantly reduced.

2. Fit a chain stopper operating aural and/or visual alarm on the mooring tension indicators fitted on the bridge panel.

3. Install an additional viewing point aft of the chain stopper assembly but high enough to enable a watchkeeper to sight the chafing chain and pickup rope.

4. Review the Safety Management System (SMS) operating on board Randgrid to ensure that the system complies with, and contains, all the functional requirements for effective and safe operation of the Code. Particular reference should be made to establish authority and communication between ship and shore during an emergency.

Conoco Ltd, Tetney Oil Terminal is recommended to:

5. Review current practices regarding onboard liaison between ship masters and berthing masters, to ensure that both parties are fully aware of each other''s responsibilities, and that a full and open dialogue is maintained at all times between the two parties.

GLOSSARY OF ABBREVIATIONS AND ACRONMS

SGS - Societe Generale de Surveillance SMS - Safety Management System

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