Use your lungs and your buoyancy compensator (BCD) to keep yourself neutrally buoyant (or close to neutrally buoyant) during the entire descent. Keep in mind that:
• A diver should be able to control his buoyancy well enough to stop at any moment of the descent and quickly achieve neutral buoyancy.
• A diver should also be able to complete the descent without touching the bottom.
This type of descent is a required skill in PADI Open Water Course (called a controlled descent without a reference).
Why Learn to Control Your Descent?:
The ability to make a controlled descent is important for three reasons:
1. If a diver experiences ear equalization problems and he cannot arrest his descent, he risks an ear barotrauma.
2. A diver must be able to descend without landing on the bottom because even a gentle fin kick can irrevocably injure coral or other aquatic life. Landing on a shipwreck or cave floor can not only destroy delicate historical information, it can stir up sediment to the point that visibility is dangerously reduced.
3. A diver should be able to stay close to his buddy during descent. A diver who plummets to the bottom will be unable to assist a buddy making a slower descent.
Step 1: Understand the Use of the BCD:
The buoyancy compensator (BCD) is not an elevator. Do not deflate the BCD to go down and do not inflate the BCD to go up. Using the BCD for these purposes only causes loss of buoyancy control. The only reason to deflate the BCD is to compensate for excessively positive buoyancy, and the only reason to inflate the BCD is to compensate for excessively negative buoyancy (thus the name “buoyancy compensator” and not “depth control device”). Only adjust the BCD to achieve neutral buoyancy, not to move up and down in the water. To ascend and descend, use your lungs and, in rare occasions, your fins, but never, never, your BCD.
Step 2: DO NOT Dump All the Air From the BCD to Begin the Descent:
Do not deflate the BCD until you plummet downwards like an anchor. To control your descent, you must first establish neutral buoyancy at the surface. Deflate the BCD incrementally until you float at mask-level with your lungs full of air and sink a little when you breathe out. This indicates neutral buoyancy. With practice, you will learn to deflate the BCD to exactly this point in one shot, but for now, deflate the BCD a little at a time until you find neutral buoyancy.
Step 3: Exhale Fully to Begin Your Descent:
Once you are neutrally buoyant at the surface, begin your descent by exhaling fully. This takes some practice as you must exaggerate your breathing. Exhale all the air out of your lungs slowly (with the regulator mouthpiece still in your mouth) and then hold the air out of you lungs for a few seconds. Try this now: exhale, exhale, exhale, exhale more, more, and now hold the air out of your lungs, try to exhale even more. . . good! The exhalation process should take around 10 seconds. Expect to slowly sink near the end of the ten seconds, and be patient. If you find yourself back at the surface when you inhale, deflate the BCD a little more and repeat the process. When performed properly, the exhalation will move you far enough down in the water column that the air in your BCD compresses, and you begin to sink slowly.
Step 4: Reestablish Neutral Buoyancy:
Allow yourself to float downwards until you can no longer easily control your buoyancy with your lungs. Once you reach the point that you continue to sink when you inhale, you are no longer neutrally buoyant. When you are neutrally buoyant you should rise slightly when you inhale fully. Remember, the goal is to maintain neutral buoyancy throughout the descent, not negative buoyancy. Add a tiny, tiny amount of air to your BCD. You should be able to stop descending or rise slightly when you inhale. Take some time to find this point of neutral buoyancy.
Step 5: Regroup:
After descending a few feet and reestablishing neutral buoyancy, take a moment to check that your ears are properly equalized. Look at your depth gauge and notice if you are approaching or have reached your intended depth. Check on your buddy. If all is good . . .
Step 6: Descend by Exhaling Once Again:
Once you have regrouped, continue your descent by exhaling fully. The goal is to control your descent by working your way slowly and carefully down through the water column using you lungs to descend and your BCD to keep yourself neutrally buoyant. When you arrive at your desired depth, you should have to do very little to fine-tune your buoyancy.
At the beginning, yes. The first few times you attempt a truly controlled descent, you will find it time consuming. This does not mean that learning to control your descent is not valuable.
As you gain experience with controlling your descent, you will become more efficient and effective. Eventually, you will deflate exactly the correct amount of air from your BCD in one shot, exhale and float down, add air to compensate for the increased negative buoyancy at the correct moment, and continue quickly down.
Once mastered, a controlled descent is more efficient than dumping the all air from your BCD at the beginning of the dive because you do not waste time fighting with your buoyancy on the way down. You arrive at your desired depth neutrally buoyancy and ready to swim off on your adventure. Be patient. Every diver can properly control his descent with understanding and practice.
Kathy Dowsett
www.kirkscubagear.com
Reprinted from About.com
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