Buoyancy and air consumption

[Uncle Pug]

if you think about your breath, then you are going to consume more air without a doubt

I think about every inhalation and every exhalation.

 

[Kim]

I think about every inhalation and every exhalation.

The way I heard it you don't breath!

 

[Jason B]

I just want to add that you need to establish your weights with an empty tank so that you will be neutrally buoyant at the end of the dive (to facilitate safety stops). You said you were trying to use your breath instead of your BC for buoyancy control. If you have a BC full of air, exhaling isn't going to help you descend to much, likewise, if you are at depth and your BC contains no air, inhaling probably won't help to much. The two need to be used together. Use the BC for gross adjustments, and breath control for fine tuning. Remember that as you ascend, the air in your BC will expand and all the exhaling in the world is not going to slow down your ascent rate...you need to use that BC (stands for buoyancy compensator) to assist in your buoyancy control.
As for air consumption, experience will take care of that.

jason

 

[Henryville]

New divers tend to use up a truckload of air messing with the BC, so I think you are on the right track with trying to use your lungs. After you reach max depth on a dive, you really shouldn't need to add gas to the BC again - modest adjustments made by breathing, large ones on ascending by venting gas from the BC.

You can actually achieve a surprising range of control by controlling your breathing, and like Pug says that requires thought. You can, for example, breathe from the "top" of your lungs (get a relatively high lung fill and inhale/exhale without fully emptying) or the "bottom" of your lungs (do a full exhale and I mean squeeze it out) with subsequent inhale/exhale not fully filling the lungs. Also, there is a balance you need to develop a feel for - your buoyancy will not change immediately from equilibrium, nor will you be able to stop an ascent/descent immediately when you make adjustments with your lungs (or BC.)

Kim is spot on in citing position in the water. The function linking cross sectional area to swimming effort is non-linear. You will use a lot more effort and therfore gas moving with a semi-vertical posture than a true horizontal posture.

A good thing to do would be to take a focused buoyancy course from a really good instructor, and to consciously think about and PRACTICE these techniques until you begin to master them. Get your weighting and trim right, work on these and you will see your air consumption drop. Longer-term, you might also want to work on physical conditioning (ugh.) Aerobic exercise will help the machinery run more efficiently on land and under the sea.

 

[SquattingRadishDM]

I'm a new diver focused on improving neutral buoyancy while minimizing air consumption.

Both these things are aided by correct breathing technique and control. Whilst big statements like "breathe slower" and "relax" are valid, they fail to explain to new divers HOW to get into a slow relaxed breathing rythme.

As I practice breathing to control buoyancy I'm concerned how inhaling deeply to ascend and exhaling hard to descend throws off my breathing rhythm and causes me to use excessive air.

You are probably constantly trying to fine tune your bouyancy by exhaling and inhaling exhessively and causing you to become out of breath. Our urge to breath comes from the build up of CO2 in the blood. The brain (hypothalymus) senses the level of CO2 in the blood and triggers a breath when it reaches a threshold. When a diver exhales exhessively hard or long to decend the urge to breathe is greater than on a normal breath so the diver tends to suck in air quickly after the outward breath. This means the diver suddenly has full lungs, is more bouyant and so has to breath out hard again to get down. This cycle can repeat itself with the divers breathing rythme totally disrupted.

First of make sure you are corretly weighted, there are numerous posts already on the board about this so if you do a search you will find a more in depth response. Also others have already covered that in this particular post.

Second practise correct breathing technique. People tend (particularly when under stress) to breathe from the upper portions of the lungs which only facilitate about 30% of the gas exchange. The other 70% can be used by breathing using the diaphram (layer of muscle between chest cavity and abdomin). As you start to inhale breathe from the lower part of the lungs, the stomach pushes outward as the diaphram drops, the chest muscles should not be used during the start of the inward breath. As the lungs fill up and become about 50% full the chest muscles expand filling the upper portions of the lungs. The whole inhalation should take at least 5 seconds to complete.

When the lungs are about 80% full the outward breath begins. The lungs are emptied from the top by compressing the chest and then pulling the stomach in. Again this is done in a slow and relax rate and should take at least 5 seconds. There is a slight pause between exhalation and inhalation before the cycle resumes.

Basically as you breath in push your stomach out, as you breathe out pull your stomach in. This method facilitates gaseous exchange meaning less CO2 build up (less out of breath) and relaxation. As you are breathing slower and therefore the volume of your lungs is changing at a slower rate your bouyancy changes slower and more consistantly. Using this technique you are more relaxed and your body demands less air, also each breath lasts longer improving you air consumption.

We breathe this way when we are asleep or relaxed. Next time your relaxing watching TV stop and see how you are breathing. Or look at how your partner is breathing when they are asleep. This is a very natural way to breath. Practise on dry land before and it should help you when you get under the water.

Simply saying "dive more" will help yes. But it will only help because the diver will go through the same trial and error and other learning experiences that you may done. I would prefer to have some background knowledge to work to rather than discovering it for myself over 50 or whatever dives.

 

[Uncle Pug]

After you reach max depth on a dive, you really shouldn't need to add gas to the BC again

I putz around with my wing gas a bit during a dive... a little spritz on the inflator here... a little burp from the rear dump there... here a spritz... there a burp... that way I don't have to do it all with my lungs. I like my lungs and try to keep them happy.

There are multiple subtle adjustments that you can combine to produce the desire result.

 

[Uncle Pug]

One of the best teaching aids for bouyancy control is the underwater magnifying glass. The higher the power the smaller the focus range and therefore the finer your buoyancy control must be.

Unfortunately cheap glass and air are close enough in refractive index that unless air is trapped on both sides of the lense you won't get much in the way of magnification. I've made several (all ended up leaking and needing repair) by silicone sealing lexan plates to both sides of the glass.

Still a reasonable effect can be had just using a 5x power small magnifier without air trapping. That should give you an effective 2x magnification and with the small size force you to control not only your buoyancy but your positioning in the water as well (which, by the way, is another marble on the stack.)

 

[Uncle Pug]

speaking of spritzing and burping... earlier this week while diving after having eaten a hoagy bun full of cold cuts and slathered with mustard... I had to add a little gas to my wing to offset the belch through my regulator.

 

[redacted]

One of the best teaching aids for bouyancy control is the underwater magnifying glass.

How do you use this as a training aid? Is this just an extension of controlling depth by watching the floaties?

 

[redacted]

speaking of spritzing and burping... earlier this week while diving after having eaten a hoagy bun full of cold cuts and slathered with mustard... I had to add a little gas to my wing to offset the belch through my regulator.

Is this another advantage of diving dry? Like empting the wing into the DSMB?