"You gotta hyperventilate and relax at the same time," says Ralph Nonella, smiling. And he does. Floating placidly on the surface of the blue Monterey Bay waters, Nonella breathes through a snorkel--once, twice, three times--then holds his breath, lifts one fin skyward and plummets toward the bottom of the sea, a picture of grace and fluid motion as he disappears into the murk of 30-foot-deep waters.