© Ian Robertson, 2012

The Key Biscayne was a mobile marine drilling platform comprising a triangular steel barge, about 55 m across, and 6.7 m deep.  It was constructed in 1972, owned by Key International Drilling Co. Ltd, and was, at the time of its sinking, under charter to Esso Australia Ltd.  It had a displacement of 2695 tons and was fitted with three triangular truss legs, each 109 m long, which were raised and lowered by electric motors.  In the retracted position, a conical spud can, at the bottom of each leg, projected 2.4 m below the bottom of the hull.  The rig was designed to drill in up to 76 m of water to a maximum drilling depth of 7620 m.  The rig had four 25 t deck-mounted cranes, an 18 m diameter helipad on the starboard side and a four-level accommodation block for 95 people.  It was fitted with two lifeboats, one on each side, capable of taking a total of 102 people.  On tow, the legs were retracted vertically above the barge.

The towing path of the Key Biscayne and its sinking position

The Key Biscayne in happy days, with its legs jacked down and the hull out of the water.  Visible are the four cranes, the drilling rig, the accommodation block and the heli-pad.  Photo source – the web.

Just prior to its sinking, it left the Torres No 1 well site, NE of Darwin, on 17th August 1973, en route to Cockburn Sound in WA for repairs and maintenance.  It had a crew of 52 and was being towed by the Lady Sonia (1232 t) and Atlas van Diemen (1179 t).  These vessels were followed by the Argus Guard, a standby vessel that operated astern of the tow and only closed with the vessels when staff were being transferred by helicopter.  Towing wires were 58 mm IWRC wire ropes.

The first seven days were uneventful with good progress and light, variable winds.  At 22:40 hrs on 24th August, the towlines to both vessels parted almost simultaneously, possibly due to an excessive tow speed.  They were then west of Tryal Rocks near the Monte Bello Islands with a southerly wind of force 4-5, 1.5 m seas and a 3 m swell.  The tow-lines were reconnected early the next morning and the tow was resumed. 

For the next three days, the winds were SSE-SSW at force 3-5 with slight seas and a swell of 2-3 m.  The tow went smoothly past North West Cape and Shark Bay.  The weather worsened south of Steep Point on Sunday 28th August, reaching force 6-7 with rough seas and a swell of 6-7 m.  Tow speed was reduced as the rig was rolling and pitching and seas were frequently washing across the deck.  At 18:38 hrs, just after dark, the towline to Atlas van Diemen parted, as did the Lady Sonia’s, leaving the rig adrift once again.  The rig was pitching and rolling severely, the decks were continuously awash with drums, pallets and containers washing around the deck, making reconnection difficult and hazardous.  Despite this, the tow was reconnected and was resumed the next day.

The weather eased between the Abrolhos Islands and the mainland.  Water taken on board the rig was pumped out.  On clearing the lee of the Abrolhos, heavy SW swells increased and, by midnight on Wednesday 31st,, gale force winds, rough seas and 5-6 m swells caused the vessels to roll and pitch heavily as they tracked slowly south to gain more sea-room.  The Key Biscayne slewed to the left of track and weathercocked into the strong wind.

At 06:44 on 1st September, the Lady Sonia’s towline parted 30 miles off Lancelin.  Atlas van Diemen reduced power and attempted to hold the rig into the weather without putting too much strain on the line.  Both tug and tow were being driven east, towards the shore, and the rig was pitching and rolling heavily.  The tow-line jumped from its fairlead, sliced through railings and staunchions and came to rest under the port anchor fairlead.  The sea continually swept the stern of the rig.  This indicated that the aft part of the rig was flooding, possibly due to excessive leg stresses, which may have fractured the hull.  As the rig settled by the stern, water was coming into the aft pump room.  Despite pumping, flooding continued so all watertight doors on the machinery deck were closed.

It was decided to evacuate all non-essential crew.  A PAN call was made at 09:17 hrs, and a MAYDAY call at 09:28.  A charter helicopter was on site but the helicopter deck was pitching too much for a landing.  Two defence force helicopters were on the scene by 10:50 hrs, in answer to the MAYDAY call. 

The Key Biscayne in trouble in heavy seas.  A helicopter has landed
on the heli-pad on the side of the accommodation block.  The legs are jacked up and the wind-sock is almost horizontal.  Photo by the RAAF.

They winched off the first personnel at 11:10 and these helicopters departed, each with four crew.  The charter helicopter landed on the helipad during a lull in the weather and took off a further 10 crew.  By 12:30, all non-essential crew were evacuated; only 10 were left on-board.

Lady Sonia made numerous unsuccessful attempts to reconnect as the rig continued to drift towards land.  At 15:30 hrs, the rig dropped its port anchor to help reduce the drift.  With the approach of night, it was decided to evacuate and, at 16:20 hrs, the charter helicopter picked up the remaining crew and the rig was abandoned at 31º10’S, 115º11.2’E.

The three support vessels remained in the area during the night but, at about 08:30 hrs on Friday September 2nd, Argus Guard reported a debris trail leading to the location of the sunken rig at 31º10’S, 115º11.7’E.  Its position was confirmed by bathymetric survey.  The rig appeared to have tipped over backwards, snapping its legs off.  The hull lies inverted, resting on two of its legs in 41 m of water (Figure 3).  The legs lie on a limestone and sand bottom, roughly parallel, and aligned northeast.  The shallowest part of the hull, one of the conical leg spuds on its underside, is at 26 m.

That no lives were lost was due to the timely decision to evacuate.  That there was no accident or injury is down to the skill and courage of the helicopter pilots flying close to and landing on the moving platform.  The Key Biscayne is now a very popular dive wreck off Ledge Point that is well worth a visit in good weather, if you are qualified to dive to 40 m, but the site is very much ‘open ocean’.

Tracy swims inside the support leg structure. The legs of the rig form a huge latticework with plenty of room to swim through.

The rack gear on the edge of the leg dwarfs the diver

Diving the Key Biscayne
The note of Lionfish’s engines slowed, we had made our rendezvous with the Key Biscayne.  While Jon worked Lionfish into position, we kitted up.  Simon went over the side to attach a white, plaited mooring rope, as thick as my arm, to the wreck, and then another, thinner, orange one.  As he came aboard he called ‘I can see the wreck from the surface – this is as good as it gets.  In you go!’

As the bubbles cleared I looked down and yes, there was a shape down there in that powder-blue water but I could not quite make it out.  Visibility was close on 30 m!  During the rapid descent along the orange mooring rope, the shape of the wreck and the extent of the disaster came into focus.  This was no tame purpose-sunk dive wreck.  This was a wild wreck, and its sheer scale spoke of the might of the offshore oil and gas industry.  Key Biscayne is down side up.  The huge ‘A’ frame lattice girder legs had snapped off and are lying beside the wreck.  Drill rods, wire and equipment were spilled all over the floor.  Many rods were shattered and bent and one corner of the wreck had snapped off.  You could almost hear the screech of tearing metal as the huge rig, already capsized, hit the sand and limestone ocean floor.  Wow!

We touched down briefly on the ‘deck’, at 30 m, actually the flat triangular bottom of the rig, next to the huge conical foot of one of the legs.  We paused briefly, and then dropped down the last 10 m to the bottom, next to one of the legs and a huge bale of wire.  ‘Only 8 minutes here’ admonished the dive computer and the first warm familiar glow of narcosis tickled my mind. ‘Operate the camera AND watch the time – FOCUS YOUNG FELLAH!’  I slid into the leg at 41 m to admire the open triangular framework of steel tube passing into the distance.  Ladder-ways followed the inside corners of the leg on two sides.  Beautiful leading lines and a lovely perspective shot – and oh so clear!  Footballer sweeps, banded sweeps and a few wrasse socialised among the latticework.  Tracey was swimming beside me, but on the outside.  I wanted some human interest and a scale for this – Tracey!!  She obligingly moved into the framework.  Not much light – hold steady and try it anyway - click. We swam on. 
Sketch-map of the wreck showing the triangular barge lying capsized, damaged and resting on the snapped off legs.

Beautiful leading lines are provided by the latticework of the legs

Ascent up the mooring rope

Soon the computer was saying ‘only 2 minutes left!’ and the leg still stretched away into the distance.  We left the framework of the leg and ascended slowly to 30 m.  From here the legs looked like a roof without the tiles.  We could see the other legs and the huge linear rack gears used to wind them up and down, somewhat softened by marine growth.  We worked our way back to the deck, where there were some lovely clusters of white soft corals and a lionfish amongst the wreckage further on, his bright colours bleached by depth.  Crays everywhere! 

Soon, the computer became insistent again, so we began the slow ascent along the mooring rope, stretching into the distance, to join the others at the safety stop, amidst dangling emergency tanks and regs that were lifting up and down as Lionfish rolled in the ocean swell.  We stretched out the safety stop in the clear blue water, as we had been quite deep, and watched the others as they climbed out.  A weight belt shot past me, to join the wreckage below, then an undersize cray headed for the bottom.  I let them go!  Then a wrist compass dropped past Tracey, which she intercepted.  Soon it was our turn to climb out.  The dive step at the back of Lionfish was deeply awash at times. 

Some of the huge machinery of the oil and gas industry
Tracy drops off the inverted barge. One of the spud feet is behind her.
Hisayo checks out the colours of the sponges and soft corals
now growing profusely on the wreck
The tangle of wreckage beneath the barge with Hisayo for scale.

Dry off, a good meal, a long surface interval and another dive, this time to look at the wreckage of the rigs superstructure, which was trapped beneath the rig.  Our torch beams revealed mysterious dark, rather tight spaces, cluttered with tangles of steel cable, crates and rope.  The seabed was cluttered with broken, torn and contorted steel structures dotted with red sponges and rotting wooden beams flecked with weed and algae.  There is nothing small about the Key Biscayne.  Massive gearwheels and other machinery is evidence of the might of the oil and gas industry.  Even the wobbegong and the Port Jackson sharks are huge and don’t seem to fear divers.  Again a short dive but fantastic.

The Key Biscayne is still one of my favourite wrecks, but the weather has to be kind.  In all, I have made five trips there, and enjoy it every time.  Each time I go back, the outlines of the wreck have softened a little with more marine growth, the underneath of the wreck has deteriorated and collapsed a little more, but the sea-fans and corals are larger and more profuse and the fish life is more abundant and varied.

Fish-life is abundant around the wreck.
The tip of the spud foot at the top of the wreck with Hisayo for scale.
A large Port Jackson shark dwarfed by wreckage.
The safety or deco stop with dangling spare rigs and relaxed divers.

Underwater pictures taken on Fuji Provia film with a Nikonos V and subsequently scanned.

Some of this was published as an article in Dive Log Australia in February 2002 Number 163, p33.