Your diving questions answered.

Q: What is the minimum bottom time needed for a dive to count as a "logged" dive?

A: Log any dive you want. Really. It's your logbook, and it's primarily for keeping track of your experiences so you can look back on them later. If you go in the water and have an experience--good or bad, short or long--there's no reason to ban that dive from your logbook. Checkout dives, especially in the Open Water class, can be a different story as most training agencies do set a minimum bottom time for training dives--generally 20 minutes--but this rule is for instructors, to ensure that they have enough time to check you out and that you get the most out of your learning experience. Also, some instructors may examine their students' logged dives during a divemaster or instructor class. But no matter what the circumstances, a logged dive that's a little short is still better than no record of the dive at all.

Q: I'm an advanced diver with about 50 dives. I'm fairly con-servative with my air, and I've recently shed all but about five pounds of my ballast weight. Can you suggest anything to further help with my gas consumption?

A: The main controlling factors for gas consumption are buoyancy control, trim, gear streamlining and swimming technique. The next time you dive, check your buoyancy while lying face-down in the water in a proper swimming position at a depth of 20 to 30 feet; with minimal or no movement, you should be able to hover motionless and stay in this swimming position for one to two minutes. Achieving that degree of trim control will dramatically improve your gas consumption. (For more details, see "Finding Proper Trim," November 2007 issue.) Next, streamline your equipment and swimming technique. Before you enter the water, make sure your octopus, console hoses, dangling straps and accessories are tucked away. With streamlined gear and good trim, your swimming technique will naturally improve, but keep these steps in mind as well: Hold your arms at your side or crossed tightly in front of you--swimming with your hands is ineffective and produces drag. Focus on long, slow fin strokes, keeping your knees as straight as possible. This requires less exertion and propels you farther with every stroke.

Finally, the best way to improve your buoyancy control and gas consumption is to keep diving. I tell my students that the first 50 dives are for learning all the things they need to correct, and the next 2,000 are for correcting them.

Q: After weight-loss surgery, I no longer need additional weight with my usual equipment: stainless-steel backplate, steel high-pressure 100-cubic-foot tanks and a three-millimeter wetsuit. Should I change my configuration (e.g., aluminum backplate) to have ditchable weights?

A: This is a common problem among divers using technical-style backplate and harness setups. It comes down to this: Can you swim your equipment to the surface without assistance in the event of a total BC failure? If the answer is yes, you should be OK. If the answer is no, you need to make some modifications to your equipment. Unlike steel tanks, aluminum tanks tend to float when they're empty, which would provide some positive buoyancy at the end of the dive, and switching from a stainless steel to an aluminum backplate would also get rid of some weight. Another option common among technical divers is using a redundant buoyancy device, either by stacking two small wings on your backplate or using a dual-bladder BC; both require a separate inflation system that you can use in an emergency. Also, a large surface marker bag or lift bag can provide surface flotation if necessary, but you'd need to swim to the surface before inflating the bag.

Q: After reading an article about lead poisoning and its effects in humans, I realized that many divers handle lead weights every day, especially divemasters and dive shop employees. They probably thread several weight belts with lead every day, which may cause lead dust exposure. What really concerns me is that I've never seen any warning in dive literature or dive courses about the dangers of lead ingestion or skin absorption. Is this a real danger for divers?

A: I spent a considerable amount of time looking for a study about this, and I couldn't find one. As far as I can tell, the answer is no. Quality weights from mainstream manufacturers are not just lead; they contain other metals (like antimony), making an alloy that is much harder than pure lead, which is very soft and bends easily. These alloys do not flake or dust significantly. Even without the danger of lead poisoning, weights made of pure lead would be impractical because after getting banged around a few times, the soft metal would deform. The belt slots would begin to close up, making them difficult or impossible to thread onto a belt, and sharp edges would develop along the exposed surfaces that might cut or fray exposure suits, BCs and other equipment.

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