There's no denying that peak performance buoyancy control separates the dive paddlers from the pros. When all the big talk is over and the water closes over your head, there is nothing that pulls the whole scuba diving thing together like perfect buoyancy control. If you drift effortlessly through your dives, if you can hover undetected only inches from delicate tube worms, and if you can make a safety stop with your chest at 15 feet, you might just want to pat yourself on the back and move on. If you think there may be room for improvement, read on.
The secret is pinpoint buoyancy control, and it all begins with fine-tuning your weighting — that's how much lead you thread on your belt or put into your pouches. If you are carrying just the right amount of weight, you will have the smallest amount of BC inflation. That means less drag and more efficient finning. Less BC inflation also means less buoyancy shift with depth, so you'll make fewer adjustments.
I've often watched divers cobble weight belts together with bits and pieces from a rental or charter boat stash and wondered just how many of them knew exactly how much weight they needed or where to best position it. I wondered particularly hard about divers about to make their first dive in a thick wetsuit who had perhaps been certified in warm water. It takes a few dives to get comfortably familiar with the significant weight needed with lots of rubber. Not getting this fundamental buoyancy issue right has consequences ranging from simple inconvenience to the potential danger of an uncontrolled descent with too much lead. Running through an imaginary dive with an eye to buoyancy control reveals a few interesting details. Many of these require total mastery of the obvious.
Take a course. PADI offers a course in buoyancy and weighting called "Peak Performance Buoyancy." The course teaches precise buoyancy control, streamlining, weight and trim adjustment, equipment configuration options and relaxation techniques.
Pre-dive preparation. Real buoyancy control begins, as does any dive, with pre-dive preparation. As you pack and check your equipment, double-check to make sure nothing has changed that could affect initial weighting. New wetsuit? Major factor. Nice, springy wetsuits need more weight than old rancid flatties. A fresh suit has more inherent buoyancy at first because diving, especially deep diving, simply bursts its bubbles. New BC? Unlikely to have a major effect at this point, but it will in the water. New weight belt? Maybe a nifty new shot belt? Take a moment to make sure the new compares well to the old. Stick 'em on a bathroom scale; often there is variation between claimed and actual weight. New cylinder? Another biggie. Some cylinders are negatively buoyant when full and simply less negative when empty; others sink first and float later.
Do a buoyancy check. Here's how to make a proper buoyancy check: With your lungs half-full, you should float at eye level with no air in your BC. But the fact that your average cylinder loses about 5 pounds as it empties gets you thinking about the buoyancy change in a tank and is a good reminder that it's best to do a buoyancy check with a nearly empty cylinder before you dive. This is obviously a bit of a pain, so add about 5 pounds to your weight if you have done your buoyancy check with a full one. You can always take a moment and recheck buoyancy before you exit. See our Buoyancy Calculator for more tips on being properly weighted.
During the dive. Now for the dive itself. Understand why feet-first descents have many advantages: One is that it's easiest to completely empty your BCD in this position. Double-check that the point where the deflator hose attaches to the bladder is really the closest point to the surface as you prepare to descend. It's often helpful to dip your opposite shoulder. Exhale, and if you're properly weighted, you should sink slowly. Keep your hand on the BC inflator and get ready to add controlled bursts of air to adjust your descent rate. You'll add more as the descent continues. If you're making a deep dive for the first time, it can be a bit of a surprise to see just how much air you have to add as you continue. During the dive, enjoy the fruits of your labor. Concentrate on what happens as you breathe. If you see something interesting below you, exhale and drift down for a look. Inhale and you'll level off and start to rise. Don't vary your breathing habits too much, though; breathing slowly deeply and continuously is of primary importance.
During the ascent. Keep the point about BC positioning in mind while making gradual ascents too. It's easy to trap some air in an unfamiliar BC, which will continue to expand as you ascend. On deeper dives, and given neutral buoyancy, you should only have to start swimming up a little before expanding air takes over. Make sure you're ready to vent this off as needed.
Make the safety stop count. The goal is to be neutral while doing your end-of-dive safety stop, so that's when you can really fine-tune your buoyancy. As you near the surface, stop at 15 feet. After three minutes, kick slowly for the surface. If you have done everything right, there should be no air in your BCD as you break the surface. You should also now be floating at eye level, rising a little as you inhale and sinking slowly as you exhale. If this is not the case, make appropriate adjustments before your next dive.
Log it. After each dive, write down what exposure suit you wore, what equipment you used, how much lead you carried, how much your body weighs and whether you seemed too heavy or light at your safety stop.
SALT WATER VS. FRESH WATER WEIGHTING
If most of your diving is done in freshwater springs or lakes, then ballast calculations should be done in freshwater. If you dive mostly in the ocean, then do the calculations in saltwater. If you switch back and forth, you’ll need to adjust your ballast needs as you go. Be prepared to add anywhere from 4 to 7 pounds going from fresh to saltwater.
See our Buoyancy Calculator for more details on making the weighting conversion between saltwater and freshwater.