Adding air to BC (how often)

[novalyne]

Hi all. I am new to diving - I have my OW dives plus about 5 practice dives. I'm trying to learn as much as possible by reading ScubaBoard. My question is about when to add air to the BC.

I have done a weight check and am pretty confident that I'm properly weighted - or within a pound or two. I have not gotten deeper than 35 feet yet, and usually am around 25-30 feet. I haven't had a chance to just sit and practice hovering, but when I do stop for a short time, I notice a VERY gradual sinking even if I take a deep breath. This tells me I need to add air to the BC - usually by this point, I've added 2 or 3 very small puffs. I never rise up when I do these practice hovers, but I can't stay in exactly the same spot either...I just creep downward.

The reason I'm confused is because I was told by my instructor and another experienced diver that they never have to add air to the BC until they get to their desired depth and then level off. I get the impression that it's a bad idea to have to add too much air to the BC underwater. But as I get deeper, isn't adding air to the BC going to be necessary?

Sorry for the length...I guess what I'm trying to figure out is whether there's a general rule of thumb about adding air. For example, is it normal to have to add air every 10 feet? 20 feet? Never? If I'm truly properly weighted, should I still expect to have to add reasonable amounts of air to the BC? Thanks for any advice!

 

[Arete]

Hey, welcome aboard!

If I'm diving a good profile (deepest point first - moving shallower as the dive progresses) I add air to my BC once, when I get to my desired depth (or more accurately as I approach it, so as to not crash into the wreck/bottom!) If the profile can't be done this way, I'lll add a bit as I go deeper.

Adding air as you descend shouldn't be necessary unless you need to slow your descent (ear toubles etc).

And as far as I'm aware, adding air to the BC underwater is fine It's what it's there for. Also you'll shed the weight as you progress and get more comfortable in the water. The amount of air in your BC will depend on your equipment, tank material, depth, body type, ad infinitum - but you will probably require some air in the BC even when properly weighted.

I'm sure other, more experienced divers will be along shortly to correct me or fill in any missing info

 

[Walter]

I was told by my instructor and another experienced diver that they never have to add air to the BC until they get to their desired depth and then level off.

That works, but there's more than one way to skin a cat. Most folks prefer to arrive at their desired depth neutrally buoyant. You can add a little at a time as you decend or all at once once you reach depth. Sometimes folks who add it all at once bounce off the bottom before they get neutrally buoyant.

as I get deeper, isn't adding air to the BC going to be necessary?

It is if you are wearing a wet (dry) suit. If diving in warm water without a suit that will compress, you shouldn't need to add any at all (unless you have poorly designed BC with lots of passing that will compress at depth).

 

[Charlie99]

I haven't had a chance to just sit and practice hovering, but when I do stop for a short time, I notice a VERY gradual sinking even if I take a deep breath. This tells me I need to add air to the BC - usually by this point, I've added 2 or 3 very small puffs. I never rise up when I do these practice hovers, but I can't stay in exactly the same spot either...I just creep downward.
........ I get the impression that it's a bad idea to have to add too much air to the BC underwater. But as I get deeper, isn't adding air to the BC going to be necessary?

If you have the right amount of air in your BCD, then sucking in a big breath will make you rise, while exhaling strongly will make you sink.

If even with a deep breath you continue to sink, then you don't have enough air in your BCD. Some divers fear runaway ascents and therefore stay negatively weighted throughout the dive, continually finning to counteract the negative buoyancy. You should find that even if you overshoot a bit and add too much air to the BCD, that if you exhale strongly then you will sink. You have several pounds of buoyancy control available in your lungs.

I automatically and unconsciously adjust my buoyancy by my breathing. I add or remove air from the BCD to "re-center" my breathing pattern once I find that I'm tending toward deeper inhales to keep from sinking or towards heavier than normal exhalations to keep from rising.

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Unless I want to descend in a hurry, I stay pretty close to neutral for the descent. Staying close to neutral throughout the dive is easier than trying to make big changes all at once. In other words, I add air before hitting the bottom.

 

[TSandM]

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.

 

[novalyne]

Thanks everyone for the great advice.

Some divers fear runaway ascents and therefore stay negatively weighted throughout the dive, continually finning to counteract the negative buoyancy.

I think you nailed it right there. 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.

You have several pounds of buoyancy control available in your lungs.

This is the part I still need practice on. 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.

TSandM, I've read several of your posts in which you give excellent advice about trim! That is definitely on my list to work on...I feel like I'm horizontal in the water, but I'm sure that you're right and I'm fins-down enough for it to make a difference when I stop kicking.

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. I'm just going to relax a little and not freak out if I don't have it down perfectly just yet.

 

[robway034]

not for nothing but: I wouldn't get too concerned about this particular issue at the moment. Get through your dives, follow the advice of your instructor...FIRST. What I mean by "first" is; that you instructor is there an can actually observe what you are (or aren't) doing. Where you need help and where you need to be left to develop on your own.
Buoyancy is the one skill that should get better with time. In the interim, concentrate on the basic rules of safety and having fun.

 

[TSandM]

As long as you pay close attention to your depth gauge, so that you maintain the same depth as long as you want to, it won't matter, except that you will blow through your gas faster than is necessary. If you are going to be in Coz for some time, I'd work on redistributing your weight until you can hover in a horizontal position without finning. I would NOT try jettisoning weight, at least until you are absolutely sure it's unnecessary. A balanced diver with some skills can tolerate a significant amount of overweighting, but none of us has any fun when underweighted, and in Coz, you have no options if you find yourself light on ascent. There are no rocks to pick up, and no kelp stipes to hang onto, and no anchor line. Work with what you know, to optimize it. Work on your weighting at home.

 

[ClayJar]

My personal "best practice" is to maintain my buoyancy such that at any point during my descent, I can arrest my downward motion by nothing more than a very deep breath. Obviously, that means I must add air at points during the descent. Although I would not win a race to the bottom, I can descend quite rapidly enough while never being out of the breath-control window.

When I'm diving with a buddy with slow ears or diving with students, being able to pause and hover at any point in the descent is very useful. Even on "normal" dives, however, I have learned to value always being in control.

(For a dive with a strong surface current where you really *do* need to shoot to the bottom quickly, I can certainly do that, but for the vast majority of my diving, that is neither necessary nor particularly desirable.)

Anyway, so I add air during the descent. After that, I could all but disconnect the inflator hose. I don't do strongly reverse profiles (starting shallow and moving considerably deeper), so I don't have to deal with the compression from increasing depth. (The small depth changes are easily accomplished via my lungs.) So, basically, as I breathe air from my tank and as I move shallower, all there is to do is an occasional bit of dumping to stay "in the window" (i.e. within the buoyancy range where I can hold a hover with breathing alone). If I find myself slightly heavy, certainly I can add a puff, but that's an exception not the rule.

 

[pasley]

The above post and your own analysis of the situation appear to have nailed it. Reading your post about your instructors admonition about adding air, you may be misinterpreting what your instructor said. 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.

Some divers add air on the way down so we can stop above the ocean floor and not crash into it. Other divers do it all at once when they get to their desired depth. On most (but not all) dives I start adding air at about 15-20 feet so that maintain a nice s,low rate of decent and can feather out at my desired depth and not become a lawn dart crashing into the ocean floor and destroying the visibility with a cloud of sediment being kicked up. Once I reach the bottom or my desired depth I feather out by adding a short puff or two to my BC. You do however want to remain slightly negative until you reach your desired depth.

If you have to continuously fin, then you are not yet neutral. Add a very small puff and wait for the added air to overcome your downward momentum (30 seconds at least) and check again. If you are adding a lot of air at say 35 feet then you may want to check your weight at 15 feet and 500 PSI.

I will bet you are also waiving your hands in a sculling motion to keep from sinking. A neutral diver is a diver who can stay at one depth (rising and falling only a foot or two with each natural/normal breath) without moving anything. All that hand waiving is costing you a minimum of 15 minutes of bottom time due to increased air consumption (I have countless examples of this).

Welcome to the world of diving and keep practicing/diving.