It was June, and the sun was still fairly strong. The three had felt somewhat stuffy in their wetsuits on the boat, but that feeling vanished once they entered the water. Especially as they continued descending, the temperature gradually began to drop.
Because water conducted heat far better than air, people lost heat more quickly underwater than on land. Fortunately, wetsuits provided insulation, and recreational dives like this generally did not go too deep. Due to pressure, every ten meters of descent underwater added another atmosphere of pressure. Beyond thirty meters, there was a risk of nitrogen narcosis. (Ordinary recreational diving tanks mainly contained compressed air—21% oxygen and 79% nitrogen. High pressure caused nitrogen to dissolve into the body, while breathing oxygen under high pressure for too long could also lead to oxygen poisoning.)
The underwater ruins Zhang Heng and the others were headed for this time lay at a depth of around twenty-five meters. There was basically no danger at that depth. With the swimming skills Zhang Heng had developed in the Black Sail Instance, he could dive that deep on a single breath even without any equipment. Of course, in that case, he would not be able to stay below for long. He would have to head back up for air as soon as he saw the ruins.
Strictly speaking, this was not Zhang Heng's first time diving in Okinawa.
When he was young, he had gone with his parents to see coral reefs in Sanya. But that had been purely a family-oriented recreational outing. They had descended less than eight meters, stayed underwater for only twenty minutes, and had been accompanied by an instructor the entire time.
If it really counted, the first time Zhang Heng had worn equipment and remained underwater for an extended period had