As they approached the ship rib that Scotty had found they turned and swam straight out toward the reef, crossed it, then came to a halt.
"Let's tie our floats to something," Rick suggested, and Scotty nodded.
Aqualung mouthpieces replaced the snorkels, and each boy tested his flow of air, checked to be sure his mask was connected to the lung by a safety line, charged his gun, and set his watch. The watches, designed especially for underwater swimming, had an outer dial that could be set to show elapsed diving time.
Rick hooted and pointed down. Scotty nodded and they submerged. Because of their belt weights, and the weight of air in their tanks, they were just heavy enough to sink slowly. After the dive, when the air in the tanks was nearly exhausted, they would weigh about five pounds less and have a slight positive buoyancy that would help them to rise.
They found coral outcroppings and tied their float lines, being careful not to cut their hands. Rick suddenly wished they had brought canvas gloves. Scotty still wore a single rubber one.
Then, with a few strong kicks to overcome their inertia, they started down the face of the reef. It fell off sharply for about forty feet, then more gradually until sand bottom was reached at about ninety feet.
Rick felt the sensation of thrusting his face into a wedge as the pressure increased. He swallowed a couple of times and felt his ears equalize, but his mask was beginning to hurt. He exhaled through his nose and equalized the pressure inside the mask.
There were plenty of fish around now. A grouper saw them coming and ducked into his hole in the coral. A fairly large moray eel, only his head visible, watched their progress. Tiny demoiselles fluttered around them, and a pair of red squirrelfish watched from the shelter of a purple coral fan.
The coral growth was spectacular, with fantastic shapes and colors. Then, as they went deeper, the colors gradually faded to a uniform green. Rick knew from underwater flash photographs that the appearance was deceptive. The colors remained, but the quality of light changed.
Scotty hooted four times, the signal for danger! Rick looked and saw a barracuda hovering near by. He gulped. The fish was easily five feet long. Both boys lifted their spear guns just in case the 'cuda attacked, but the motion alarmed him and he was gone with one powerful flick of his tail.