Date: 01/09/1983Location: Ledge Point, Western Australia
Activity: Rig move
The Key Biscayne, owned by Key International Drilling Company, was under contract to Esso Australia and had just completed a well in the Arafura Sea, 180 miles northeast of Darwin, Australia. The decision was then made to stack the rig in Cockburn Sound near Fremantle. Two rig supply vessels, the Atlas Van Diemen and the Lady Sonia, would be used to tow the rig down the west coast of Australia to Fremantle. The Argus Guard was to accompany the rig as its stand-by vessel.
The first week of the tow along the north-west coast passed without incident. On Wednesday 24 August 1983, both tow lines parted and were reconnected by the early hours of Thursday 25 Aug. The rig then rounded the NW Cape and passed Shark Bay, experiencing slight seas but no problems. On Sunday 28 Aug, the weather began to worsen with force 6-7 winds, rough seas and 6-7m swells. On the evening of the Sunday 28 Aug, both tow lines were again lost. The rig was pitching and rolling heavily with the sea constantly washing over the main deck, causing damage to the rig from smaller cargo items which were washed around the main deck. There was some suspicion that sections of the deck plating had been fractured causing leaks, and water taken onboard during the bad weather was pumped out. By Monday 29 Aug, both tow lines were reconnected and the tow resumed in more moderate weather.
As the Key Biscayne sailed south of the Abrolhos Islands on Wed 31 Aug, it experienced heavy SW winter swells. By midnight of 31 Aug, gale force conditions sprang up with high winds, rough seas and 6m swells buffeting the rig. At 0644 hours on Thurs 01 September, the Lady Sonia tow line parted and the Atlas Van Diemen attempted to hold rig into the wind, although both vessels were being driven easterly towards the shore. The rig appeared to be pitching more to the stern than the bow with the sea continually washing over the main deck, indicating that some flooding of the aft tanks may have occurred. On the morning of 01 Sep, it became obvious that the rig was settling to the stern and the rig reported water overflowing from the aft pump room into the port-side sack room.
The worsening situation led to the decision to evacuate non-essential personnel and a MAYDAY was sent at 0930 hours on 01 Sep. By this time, a charter helicopter had arrived on scene but the pilot could not land due to the excessive pitching of the rig. Two defense force choppers were dispatched and were able to winch off eight crew, after which there was a lull in the weather and the charter chopper managed to lift off another ten. By 1230 hours, only ten essential crew were left aboard. Through the day, the rig began settling to the stern and listing to starboard, with heavy seas washing over deck. The bow was observed lifting clear of the sea, with the rig pitching 10 degrees forward, 25 degrees back and rolling 15 degrees to each side. The rig's Manual of Operations specified that the rig's pitch or roll should not exceed 5 degrees.
After a number of unsuccessful attempts to re-attach the towline, all line-throwing rockets had been used and conditions on the deck became too hazardous for work. Ten nautical miles off Ledge Point, the rig's port anchor was let go to help hold the rig. The remaining crew were then evacuated at 1620 hours, with the intention of returning the following day.
At 1730 hours, the rig anchor parted. At 1845 hours, the Atlas Van Diemen towline parted. The Argus Guard then turned to starboard to clear the rig. After the turn, the rig was no longer visible and radar contact had been lost. The rig had capsized in 41m of water, landing inverted on the seabed with two of its legs bent or broken under the rig. The third leg lay broken off away from the rig. The attitude of the rig on the seabed indicated that it had tipped over backwards.
Causes
Loss of directional control and gale force conditions were cited as the main factors in the accident. Loss of watertight integrity and flooding through possible hull fractures caused by excessive leg oscillation experienced as the rig pitched and rolled were also named as contributory factors.
Sources
Australian Transport Safety Bureau: Preliminary Investigation
Photos: DIRdudes & Image Dive & Charters
