Ten minutes later they reached the southern end of the reef. The location was obvious both by the trend of the reef, indicated by the compass on his dive computer, and by the increasing strength of the current pushing them. Also the shape and colour of the seabed began to change. As they rounded the curve to the southern end of the reef the bottom sloped gradually down on their left to a sandy valley which shaded into dark blue depths.
The Bramble Boat Passage, Andrew thought.
From studying the chart he was able to visualize the channel. He knew that the Boat Passage branched off from the main Challenger Channel near Prescott Island. It then ran Southwest gradually getting shallower. At its junction with the Challenger Channel the Boat Passage was one hundred and twenty-five fathoms deep, over two hundred and thirty metres, deep enough for the largest of ships, but by the time it reached the half-kilometre wide gap between Yule Reef and the Five Feathers Reefs to the south it was only five fathoms, nine metres. This was why it had never been suitable for ships to use, unlike the Challenger Channel which was still forty fathoms, over seventy-five metres deep at its shallowest.
The bottom is all sand and this end has a bathtub shape, Andrew remembered.
A careful look around seemed to confirm this as he could see the sandy slope rising from the deeper channel and then reaching an obvious crest off to his front. Beyond that the water became deeper again as it shelved away on the western side of the line of reefs.
Andrew noticed movement out to his left, well away from the reef. What is that? he wondered anxiously. Then he saw that it was Carmen and Tristan. They were right down near the bottom and were swimming directly away from the reef. Where on earth are they going? Andrew wondered. He could not remember any part of the plan about going south across the Boat Passage.
Quickly he checked his compass. Yes, they are going across the Boat Passage. That both puzzled and worried him. If they aren’t careful they could get caught by the current as the tide gets higher, he thought. That could sweep them off to the west and give them a hard swim to get around behind Yule Reef to where the dive boat was anchored.
Andrew looked around and saw that Ella was also looking. She gave a shrug but Andrew shook his head, then moved to check her air pressure. ‘95,’ he signalled. He looked at his own and it informed him that he only had 75psi left. That worried Andrew a bit as he knew he should keep about fifty in case of emergencies and they still had a few hundred metres to swim to get back to the dive boat.
But I have only been swimming at about five metres, he thought, so I shouldn’t have too much nitrogen to dissipate.
As he worked this out Andrew watched Carmen and Tristan. They were now on the limit of visibility and that got Andrew even more anxious. Now undecided about what to do he looked up and noted that the inflatable was moving out across the Boat Passage as well, obviously following the trail of bubbles.
Where are they going? he wondered. Then he noted a dark bump on the seabed out on the crest line. And what is that?
Whatever it was Carmen and Tristan were obviously going to investigate it. Probably just a rock or small outcrop of coral, Andrew surmised. But even as he did this his eye noted a straight line half-hidden in the sand of the seabed. It came from down to his left and ran across the seabed towards the dark hump.
What the devil is that? Andrew wondered, pointing to it to bring it to Ella’s attention.
It was clearly not natural, and Andrew guessed that it had attracted the attention of Carmen and Tristan. He had been about to swim on around the end of the reef and back to the dive boat but now he signalled to Ella that he was going to join the others. She shook her head, but Andrew was determined. Where Carmen was going he was going.
Quickly he printed on the back of his slate: We can always surface and go back in the boat.
Ella read this and gave a thumbs-up. Andrew at once began swimming, angling slowly down towards the straight line on the sand. To reach that he had to go down to fifteen metres but that did not bother him at all as he was qualified to go to thirty. As he went down Andrew noted that the current was moving him sideways to his right so he had to ‘crab’ to the left across it to reach the line.
As he got closer Andrew saw that it was not one line but a pair of steel wire ropes. Curious he swam right down and touched one to check. Two steel wire ropes lying side by side, both new and in good condition, he noted, grimacing with annoyance as the rope was coated in some sort of grease.
Looking to his left he saw that the ropes ran down into deeper water and then ended abruptly at what looked like a pulley block.
Curious to see if he was right Andrew swam that way, going another five metres deeper as he did. It was a pulley block. The block was shackled to a steel ring set in what looked like a large block of concrete. The concrete block was almost completely buried in the seabed.
What on earth is all this? he wondered.
Andrew looked around at Ella, who was close beside him. She met his eyes and shrugged. Andrew also shrugged, then checked both his depth and his remaining air. Still got 65psi, he thought.
Ella informed him she had 70psi. Andrew knew he was now moving into a potentially dangerous phase if he stayed down much longer but he reasoned that he would be going back slowly upwards if he followed the ropes.
They are going to that lump on the crest and it is only at five or six metres, he reasoned.
So he turned and swam back along the steel wire ropes, heading for where Carmen and Tristan could just be made out as tiny moving shapes at the dark mound.
What is it that they are looking at? Andrew wondered.
Chapter 2
STUNNED
As he swam quickly towards where Carmen and Tristan were Andrew puzzled over what it could be that they were looking at. From his study of the chart he did not remember any isolated rock or coral outcrop being marked in the middle of the Boat Passage.
And why has this steel wire rope and anchor point and pulley been put here? he wondered.
The whole group of reefs was in a restricted research conservation zone so there should not be anything artificial there. It wasn’t even one of the anchor buoys that had been placed at selected places by the Great Barrier Reef Marine Park Authority. Andrew noted that the wire rope ran directly to the dark mound.
It only took a couple of minutes for Andrew and Ella to swim the hundred metres to where Carmen and Tristan were pulling at something on the dark lump. As they were swimming with the current they were able to skim along. The only thing they had to do was keep watching their depth so they did not come up too fast. Twice Ella caught Andrew’s eye and tapped the dive computer on her wrist to remind him of both the depth and the time. He nodded and gave a thumbs-up.
Another quick check of remaining air showed that Ella had sixty-five and Andrew fifty. That was now becoming serious and he nodded to show he understood. But they were now only a short distance from where Carmen and Tristan were pulling at what looked like a net. So Andrew continued swimming, confident he could safely surface and reassured by the sight of the rubber boat bobbing only ten metres overhead.
But even as he looked up the rubber boat began moving, the propeller on its outboard motor becoming a sudden whirring blur and its engine noise very obvious. It sped away westwards.
Where is Dan going? Andrew wondered. Must be back to the dive boat for something, he decided as it was anchored in the direction the rubber boat was going.
Still curious about the net covered mound on the seabed Andrew switched his attention back to the dark mound which he now saw was the size of a large vehicle.