Adding air to BC (how often)

[ClayJar]

In your post you said "...my instructor's admonition against constantly adding/reducing air..." indicates he is talking about avoiding the yo-yo game. Yo-yo game-adding air, not waiting for it to overcome your downward momentum, adding more air, then floating up, dumping and repeating.

One key that I know doesn't get stressed enough around my local area could, perhaps, be phrased "Take control."

Any time you have new divers, you're going to see people occasionally starting to float up. (If the class is good, the issue will be knocked out in the pool.) There seems to always be at least one, however, that starts floating and immediately thinks, "I'm floating. I should dump some air." That's a perfectly logical analysis of the situation, but there's slightly more to it than that.

If you're floating up, and you just sit there and dump a little, then dump a little more, and so on, by the time you've dumped enough to be neutral, you're a bit (maybe more than a bit) shallower than you were. If you built up a bit of upward momentum, you may even need to become a bit negative to arrest your ascent. Either way, what happens when you descend back to your original depth? Yep, the air in your BC compresses, reducing your buoyancy, and requiring you to add air. If you add just a bit too much, the yo-yo cycle starts right over again. (This is where you can easily get stuck in the loop, constantly adding or dumping.)

What should a diver do, then? As soon as you feel yourself floating up, the *first* thing you do is *take* control of yourself. Use those wonderful fins to stop yourself from floating shallower (you just tip over slightly and kick). You now have *taken* control of yourself, so at that point, you solve the problem by dumping a little air, and repeating as necessary, until you're neutral again.

As long as you *take* control and don't just "let diving happen" to you, you don't need to try to rush to dump enough air to arrest an ascent. You've already stopped the potential ascent by simply kicking to hold depth, so you have as much time as you need to ease yourself into comfortable neutrality. Since you're not floating shallower while you get neutral, you won't have to add air to account for compression as you get back to your original level -- you've basically never strayed much at all from that depth.

The more experience you get, the more of a feel you get for buoyancy. I never actually float up during a dive, as I can feel the changes in my breathing and dump air while still "in the window". Even with new student divers trying to learn buoyancy skills, however, as long as they learn to *first* take control and *then* solve the problem, the yo-yo problem pretty much goes away completely.

 

[Charlie99]

The idea of an uncontrolled ascent, combined with my instructor's admonition against constantly adding/reducing air in my BC, has made me paranoid about how often I should be having to add air.

I don't have a "feel" for it yet and I suspect I'm trying to rely solely on my lungs instead of using the BC appropriately.

Safety stop at the end of dives is a great time to work on buoyancy control. Try hovering horizontally -- that gives you more drag in the vertical direction and makes it easier to maintain depth. I kind of like doing the fin pivot exercise common in OW cert classes, but doing it in midwater with nothing touching the bottom. If it helps to get dialed in, then go ahead an do fin pivots on a shallow bottom, adding more air to the point where a very full lung pulls you off the bottom.

Another thing you could try is to purposefully put a bit too much air into your BCD (preferably at the beginning of a dive where you don't have much nitrogen loading) and then see how a strong exhale can still stop your ascent.

A great side benefit of learning how to get truly neutral is that you can stop finning anytime and just hang there. Very relaxing compared to the "gotta keep finning" feeling you subconsciously feel when you are negatively buoyant. This typically results in greatly decreased air consumption.

I'm going to Cozumel in a few days and I was worried that as I dive deeper, it will become an even bigger issue.

Deeper is easier. When deep, your buoyancy doesn't change as much with depth changes. The most difficult area to control buoyancy is in the shallowest 20' or so.

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A lot of people confuse the issue of neutral buoyancy with that of being overweighted (wearing to much lead). They are different, although sometimes related, issues. You can be overweighted and still use your BCD to stay neutral throughout the dive. You can be properly weighted, and if you don't add enough air to your BCD at depth, then you will be negatively buoyant.

Having the correct amount of lead makes it easier to stay neutral with depth changes. Having a thinner wetsuit also makes life easier because your buoyancy changes less with depth. Having extra lead, extra neoprene, or both makes life more difficult.

 

[diver 85]

maybe once or twice a dive?, I really don't keep up with it but you'll get ALOT more comfortable in a couple hundred more dives....For right now, don't worry about it, as long as you make a 'safe' dive, you're OK....

 

[Gombessa]

I like slow, controlled descents, face to face with my buddy(ies). That way everyone has an eye on each other and problems (many of which manifest at the beginning of a dive) are seen and dealt with in a timely manner. It also means you need to control the rate of descent, so we try to let enough air out of the wing just to start sinking, and gently tap the power inflator button on the way down to keep that rate steady.

I know there are instances where you want to get down in a hurry (strong current, etc.), in which case you'd have to adjust the speed and strategy accordingly. But generally, an uncontrolled, speedy descent toward the hard floor of your dive plan is not the best time to discover that your inflator hose came loose.

 

[novalyne]

Thanks again for all the excellent advice. You all have given me a lot to think about and practice on my upcoming dives.

 

[Bob Vincent]

I add air to SOMETHING every time I clear my ears on descent. (I dive a dry suit, so sometimes the air goes there, instead of into my BC.) That keeps me negative enough to continue descending, but not so far off neutral that, when I see the bottom coming up, I have to blow a huge amount of gas into anything. (In Puget Sound, you may descend a LONG way before you see any bottom below you.)

If you are finding that you are always a little negative (and, by the way, major kudos to you for looking into this in this way), it may be because you are diving in a feet-down position. If you are feet-down, every time you kick, you are driving yourself upward as well as forward. The only way to stay at the same depth is to stay a little negative, so the drive downward from negative buoyancy counteracts the drive upward from your fins. This is an EXTREMELY common state of affairs for new divers.

The solution is to balance your equipment, and amend your posture. You can move the tank up in the cambands, or move some of your weight up onto the bands or the neck of the tank, or trim pockets if your BC has them and they are over your shoulders (as opposed to your kidneys, which isn't much help). Your posture should be flat, just as though you were lying on the floor on your stomach, and not with the knees dropped. If you do both of these things, you will have the ability to reach and maintain neutral buoyancy and still kick yourself forward.

 

[shoturtle]

Welcome,

Once you get your buoyancy right underwater, you should be able to do the whole with what you initially put into the bc. You will end up using your lungs to bring you up and down while underwater. Take a peak buoyancy, it a good class to that teaches you to use your lung to control dive.

As you get more comfortable with scuba, you will find that you will need less and less weight. I started with 18lb with a 3mm full suit, after couple of dives I was down to 12, and now I all I need is 10lb. So as you dive more and more, you will find that you are to heavy and need to put more air. Because you will be more relax and not put as much air into your lungs causing you to lift.

 

[Charlie99]

Once you get your buoyancy right underwater, you should be able to do the whole with what you initially put into the bc.

This is not true, and there is no reason to try to do this as your goal. There are limits to what is reasonable to compensate with changes in lung volume, and the compression of a thick wetsuit (such as 7mm full + 7mm farmer john) combine with the change in tank weight of a large tank over a dive will exceed the buoyancy change available in the lungs.

You also seem to assume that every dive is an immediate descent to the deepest depth. That's not true of all dives.

You have a BCD. Use it. Use it to take care of the large changes. Use your lungs for the smaller changes and for instantaneous control.

 

[shoturtle]

As the op said he only goes down to 25-30 feet and is seem to be a warm water diver from TX, you are only at one atm. Once you get the proper buoyency at 30ft. The OP should not have to add more air to the BC. I am only answering to the conditions that OP stated.