Step 1: Proper Weighting
You should be able to get this fairly accurate, certainly within a pound or two. To determine your proper weight, you first need to know what kind of thermal protection you’ll be wearing. If you dive in colder waters where a 7 mm wetsuit is needed, start with about 10 percent of your body weight. If you dive in waters requiring a 3 mm wetsuit, try about 5 percent. And if you’re diving in a lycra skin (which has no buoyancy), you may not need any weight.
To see if you are properly weighted requires getting in the water. Wearing all of your dive gear, inflate your BC and float at the surface. With your regulator in your mouth, take and hold a full breath of air, then empty all of the air from your BC. If properly weighted, you should float at eye level. To begin a descent, all you have to do is exhale. Also remember that if you are doing this check with a full aluminum scuba cylinder, to add several pounds (perhaps five) of weight before diving. You can find specifications for many different scuba cylinders at Scuba.com. This will compensate for the positive bouyancy characteristics of aluminum cylinders when empty and keep you from being too buyoant at the end of your dive.
Step 2: Using the BC
Once you’ve got your weight set, you’re ready to dive. This is where the BC comes into play as it allows you to fine tune your buoyancy. Scuba.com has a wide selections of styles and brands of buoyancy compensators to choose from. In theory, if you start out properly weighted, you’re adding just enough air to the BC to offset the compression (loss of buoyancy) to your wetsuit. The thickness of your wetsuit will also affect the compression and your buoyancy. The two biggest things to remember when using your BC are (1) make small adjustments, and (2) remember that there’s a lag time between adding or releasing air and actually feeling the effect. One of the biggest problems divers with bad buoyancy have is that they over-adjust the BC, either adding too much air and starting an ascent, or dumping too much air and plummeting to the bottom.
Step 3: Fine Tune With Your Lungs
Proper weighting and the amount of air in your BC should allow you to get your buoyancy pretty close to neutral. The amount of air you keep in your lungs allows you to “fine tune” everything. Think of your lungs as an internal BC. Fill them up with air, and you’ll start to rise. Empty them of air and you’ll sink. (The buoyancy difference between a full and empty lung, depending on your body size, can be anywhere from five to 10 pounds.) Do you want to go over a small rise? Just inhale a little deeper. Want to sink to look at something under a ledge? Exhale fully. Did you put too much air in the BC? Exhale while you vent air out of the BC. Did you dump too much air out of the BC? Inhale fully to help arrest your descent while you add air to the BC.
Putting It All Together
Mastering buoyancy control will improve your air consumption (less drag), make you less tired (by not working as hard) and allow you to enjoy diving to the fullest. And when you do it right, you’ll feel in total control of your body positioning in the water. It’s truly an exhilarating feeling.