Damage sustained to the tanker Osco Star during cyclone Justin

Summary

On 8 March 1997, the Australian tanker Osco Star was in the southern Coral Sea south of Lihou Reefs, on a loaded passage from Geelong to Port Moresby. The vessel had been experiencing east-south-easterly gale force winds since passing Fraser Island on the evening of 6 March.

To the north of Lihou Reef, a tropical depression, moving slowly in a south-westerly direction, had been developing to cyclone status and had been allotted the name 'Justin'.

During the early evening of 8 March, Osco Star experienced a gradual decrease in the wind to force 2, then the wind backed to the east-north-east and increased in strength, indicating the vessel had passed close eastwards of the cyclone's centre. By late evening the wind had shifted to the north-north-west, at gale force, and the engine speed was reduced due to the heavy weather.

Towards daybreak on 9 March, the wind increased to storm force. At 0620, an earth fault alarm in the engine control room led to the eventual discovery that seawater had entered the emergency generator room, located on the port side of the poop deck, and was sloshing up underneath the emergency switchboard.

During attempts to rectify electrical faults in the emergency generator room, fuses were removed in the 24-volt rectifier/charger unit, inadvertently stopping all engine room pumps. The main engine, however, continued to run, and only stopped once the fuses had been replaced nearly two minutes later. At about 0841, as the fuses were replaced, there was a complete loss of electrical power.

The main engine was restarted from the emergency manoeuvring position at 0925, but short circuits had damaged the 220-volt section of the emergency switchboard, causing the loss of some engine room instrumentation. Seawater had also caused the failure of the 24-volt rectifier/charger unit. The 24-volt system had switched to battery back-up and the batteries were discharging. By about 1100, the battery voltage had fallen to the point where the contactors in the pumps automation system started to drop out. The main lube oil pump stopped, the stand- by pump failed to start and the engine continued to run until, following some confusion, it was manually stopped by the Chief Engineer.

After carrying out checks on the engine it was restarted but, at 1248, was again stopped for a brief crankcase inspection after loud metallic banging was heard as speed was increased. Nothing was found amiss during the inspection. After again getting under way, there were more noises from the engine and it was noticed, later that afternoon, that the crankshaft had moved about 25 mm forward.

That evening, debris from the crankcase, including paint flakes, white metal, shards of steel and brass shims started to block the lubricating oil strainers which required cleaning at 11-minute intervals.

The ship was nursed to Brisbane where, upon opening up the main engine, it was found that the ahead pads in the thrust bearing had been dislodged, and the crankshaft had moved at least 30 mm forward. The engine had suffered extensive damage to the crankshaft, connecting rods, main bearings (which had been carrying the thrust), crossheads and the axial vibration damper. The bedplate had also suffered damage.

Conclusions

These conclusions identify the different factors contributing to the incident and should not be read as apportioning blame or liability to any particular individual or organisation. The following factors are considered to have contributed to Osco Star sustaining considerable damage during tropical cyclone Justin:

1. Timely action was not taken to avoid an encounter with the tropical cyclone.

2. A proper appraisal of the possible movement of the cyclone was not made, and no account taken of the steady fall in barometric pressure and lack of wind directional shift, which resulted in Osco Star passing close to the centre of the cyclone.

3. There was no full exchange of views, in line with Bridge Resource Management procedures, on the developing situation and the appropriate action to be taken. 4. Reliance was placed upon the wind conditions being experienced beyond the immediate area of effect of the cyclone, rather than on the Bureau of Meteorology's predicted wind strengths.

5. The poop and boat decks were not properly secured against the ingress of water into the steering flat and the emergency generator room, which occurred during the cyclone and which initiated the events which led to electrical, and subsequent mechanical, damage.

6. The design of the bulwark around the poop deck prevented the rapid freeing of water trapped in that area and probably contributed to its ingress into the emergency generator room.

7. The design of the weathertight, rather than watertight, doors and flaps and the poor design of the access to the emergency generator room for electrical shore connections, contributed to water gaining access to those spaces which open onto the poop deck.

8. The design of the ship's 24-volt system and associated alarms was such that the battery voltage was able to drop to a critical point where the engine safety system was disabled, without the ship's engineers becoming aware of the situation.

9. The ship's staff appeared unaware of the fact that;
- Removal of the fuses in the 24-volt rectifier/charger unit would stop all running pumps including that for main engine lubrication.
- The main engine would not stop while the fuses were out.
- After failure of the 24-volt rectifier/charger unit, the system was running on the back-up batteries and they seemed unaware of the consequences of the discharge of these batteries.

10. The loss of voltage from the back-up batteries, as they discharged, caused contactors in the Pumps Automation System to drop out and the running lubricating oil pump for the main engine to stop.