You look like a sirocco down there," I heard Bob chastise Rene as they slipped out of their gear. They'd just finished their first dive from the same Southern California charter boat as my PADI Master Scuba Diver students, Alph and Kendra.

"She looked like Volkswagen?" Alph queried.

"No, 'sirocco' the dust storm,'" Bob corrected irritatedly. "Kicks up a cloud wherever she goes."

"Well, you don't exactly help the viz dragging your fins on the bottom," Rene retorted.

"Sounds like you two could use the Peak Performance Buoyancy course," quipped Kendra.

Red alert! Red alert! I threw myself behind a bench for protection from impending combat. Nothing erupted though, and Kendra continued, "Alph and I just finished it."

"Nah, we know neutral buoyancy," Bob said a bit defensively, "We just need to stay higher off the bottom." Rene nodded.

"That's always a good idea," said Alph, "but a skilled diver can swim close to the bottom and not stir it up much. There's more to buoyancy control than getting neutral."

"Like what more?" demanded Rene in an agitated tone.

Uh-oh. I hunkered down, hoping the ricochets would bounce favorably.

"Proper weighting, for one," countered Alph. "If you're overweighted, you can get neutral with your BCD, but you swim with your feet too low and your torso too high. That stirs up the bottom and wastes energy."

"Or you can be properly weighted but have poor trim," added Kendra.

"Trim?" queried Rene. A genuine question, not a challenge.

I downgraded the threat level to yellow and stuck my head out. "Trim is where your weight is relative to your center of gravity. It determines your orientation when you hover," Kendra explained.

"I get it," said Bob. "I naturally rotate into a feet-down position."

"Exactly; that's trim. You can adjust your gear and weight position so your trim holds you in a horizontal position," said Alph.

"Since you hover feet down, you could probably lose those ankle weights," noted Kendra. I returned to cover, but Bob didn't take offense. "But keep 'em in case you get lighter fins. When your gear changes, so do your buoyancy and trim."

"So what'd you do in this Peak Performance Buoyancy course?"

"Our instructor — — he's around here somewhere," said Alph, "—He started by showing us how to fine-tune our weights."

"Then he showed us how to streamline ourselves to save energy," said Kendra. "That included adjusting and distributing everything to get our trim right."

"After that, we made dives just to master buoyancy — hovering, making minor depth changes using only breath control," continued Alph, "He had us pass through a hula-hoop midwater without moving a muscle — just slowly drifting through breathing."

"Until you're trim, slim and neutral, you can't do it," said Kendra, "It's harder than it sounds until you get it right. Then it's easy."

"Is that it?" Bob asked.

"There's more — — using your mind to improve performance, the role of fitness, how your buoyancy changes as you use up air —— stuff like that," said Kendra. "Everything you learn is pretty simple and basic. The challenge lies in putting them all together at once and making them second nature when you dive."

"Let's sign up," suggested Rene. "Let's talk to your instructor. Where is he?"

"I think he's forward," said Kendra, "Stowing his flak jacket."