Buoyancy and Breathing

[aquaregia]

I've been steadily decreasing my weight since my OW, and I've also been decreasing my SAC. I'm noticing now that I'm having some trouble keeping level while I breathe, however. My position is fluctuating perhaps as much as 2' every time I breathe. I suspect this is because the air in my lungs is a larger proportion of my buoyancy now that I have less weight and thus less air in my BC, and also I'm breathing slower and deeper. I did some quick back-of-the-napkin calculations as a sanity check, and they seem to indicate that my lungs could make a buoyancy difference of between 3# and 14#, although the extremes would be fairly unlikely. I'm guessing 5# is closer to it (based on spirometry, SAC and breathing rate estimates). It seems like I have a three way tradeoff between weight, SAC and vertical constancy.

My SAC is still quite high (0.85ish) so I'd rather not sacrifice that. Should I wear more weight and keep more air in my BC? Or should I just get used to the positioning issues?

 

[Hank49]

Do you NEED to keep level? If you do, it's partly being properly weighted but the finer art is in the timing or your inhale and exhale. Just as you begin to descend even a couple inches, start your inhale to stop. And the same for when you start to ascend a bit...exhale. It takes a bit of practice and you need some reference point to see that you're motionless.
However, this may not be the most gas saving method for breathing because some breaths are shortened a bit and timed...just to maintain position, rather than inhaling and exhaling slowly purely on demand.

 

[Amphiprion]

From my understanding, the only way to avoid some variation in buoyancy when breathing is to get a rebreather. I would think that if you can maintain level with a little positive with lungs full of air and a little negative with nearly empty lungs you are doing better than a lot of new divers.

 

[Straegen]

I doubt it is weight related in the way you are thinking. The only time a diver should have buoyancy problems is when they are overweighted or at the end of the dive when their tank has lost 5lbs and they are more buoyant and struggle to stay down (not completely true but the majority of the issues fall into here). If you are bouncing at the beginning of the dive you are either overweighted or I am guessing using your breath to control your position in the water. I have started humming myself to help with this issue. I tend to relax more and breath more steady when doing this.

Do you have any air in your wing/jacket at the beginning of the dive? If so how much?

 

[elan]

I've been steadily decreasing my weight since my OW, and I've also been decreasing my SAC. I'm noticing now that I'm having some trouble keeping level while I breathe, however. My position is fluctuating perhaps as much as 2' every time I breathe. I suspect this is because the air in my lungs is a larger proportion of my buoyancy now that I have less weight and thus less air in my BC, and also I'm breathing slower and deeper. I did some quick back-of-the-napkin calculations as a sanity check, and they seem to indicate that my lungs could make a buoyancy difference of between 3# and 14#, although the extremes would be fairly unlikely. I'm guessing 5# is closer to it (based on spirometry, SAC and breathing rate estimates). It seems like I have a three way tradeoff between weight, SAC and vertical constancy.

My SAC is still quite high (0.85ish) so I'd rather not sacrifice that. Should I wear more weight and keep more air in my BC? Or should I just get used to the positioning issues?

Yeah when your total air-bubble is less and you are lighter you body tend to react faster to the changes of the lungs, so you if you add more weight it will be more stable but you will have other, more important problems.

I think you just learn to maintain the level by proper timing, this is at least what I have found.

 

[aquaregia]

I like humming actually. Any suggestions for good songs that will creep out my buddy? I'm hoping to exploit the lack of directionality to make my buddies think they're losing it.

 

[seaducer]

2 feet? Sounds like maybe you are filling your lungs up completely, then emptying them all the way as well, and doing it slowly.

Try to breathe just like you do when you are just hanging out, like now. Normal consistent breaths are usually timed so that as you are starting to rise from an inhale you are already exhaling.

It will also help your SAC since you are taking less total air in every breath. It all comes with practice, so make sure you are diving alot!

 

[LeadTurn_SD]

I've been steadily decreasing my weight since my OW, and I've also been decreasing my SAC. I'm noticing now that I'm having some trouble keeping level while I breathe, however. My position is fluctuating perhaps as much as 2' every time I breathe. I suspect this is because the air in my lungs is a larger proportion of my buoyancy now that I have less weight and thus less air in my BC, and also I'm breathing slower and deeper. I did some quick back-of-the-napkin calculations as a sanity check, and they seem to indicate that my lungs could make a buoyancy difference of between 3# and 14#, although the extremes would be fairly unlikely. I'm guessing 5# is closer to it (based on spirometry, SAC and breathing rate estimates). It seems like I have a three way tradeoff between weight, SAC and vertical constancy.

My SAC is still quite high (0.85ish) so I'd rather not sacrifice that. Should I wear more weight and keep more air in my BC? Or should I just get used to the positioning issues?

Its all about "pace". If you are trying to hold postion with full or empty lungs, you'll have a problem. If you are breathing fairly normally, you should rise and fall, but inches, not feet. If you are forcing a slow breathing rate, maybe that is where the problem is coming from.

I take deeper-than-normal breaths while diving, and try to exhale more fully, but the whole inhale-exhale cycle is maybe 8-10 seconds, with a mini-pause at each end. So just as I start to sink, an inhale begins, and just as I start to float up, and exhale begins, and the buoyancy changes mostly cancel-out.

I actually find the "lighter" I am weighted (to a point), the easier my buoyancy control is (because I have less of a bubble in my wing to contend with).

Best wishes.

Edit: As far as SAC goes: "It is what it is". I'm 6'5", 260. My wife is 5'7", 130. My SAC is never going to be as low as hers (I vary between just under .7 on a "good" day, to almost 1.0 if I'm "working" during the dive). Worry about good gas exchange with steady deep breathing, but do not force a slow rate; and in fact, just remember to breath deeply and don't consciously control the rate at all (it will adjust to fit what your body needs, hopefully), and I bet you bouncing-ball-buoyancy goes away

 

[RJP]

I've been steadily decreasing my weight since my OW, and I've also been decreasing my SAC. I'm noticing now that I'm having some trouble keeping level while I breathe, however. My position is fluctuating perhaps as much as 2' every time I breathe. I suspect this is because the air in my lungs is a larger proportion of my buoyancy now that I have less weight and thus less air in my BC, and also I'm breathing slower and deeper. I did some quick back-of-the-napkin calculations as a sanity check, and they seem to indicate that my lungs could make a buoyancy difference of between 3# and 14#, although the extremes would be fairly unlikely. I'm guessing 5# is closer to it (based on spirometry, SAC and breathing rate estimates). It seems like I have a three way tradeoff between weight, SAC and vertical constancy.

My SAC is still quite high (0.85ish) so I'd rather not sacrifice that. Should I wear more weight and keep more air in my BC? Or should I just get used to the positioning issues?

Stop thinking about how you're breathing, you'll be much better off.

 

[Sas]

I had this problem when I was new to diving. Either I breathed deeply, and had a low SAC, or I used my breathing to finetune my buoyancy and this made my SAC higher. I don't know what happened but now I can stay still and have a low SAC so I think it is mostly about practice. You get good at timing your breathing to breath in when you are *just* about to start sinking and so on.

I think it is helpful when new to pay attention to one's breathing as then you can link that in to how it affects your buoyancy. That's what helped me learn how to have good buoyancy anyway. After a while it becomes an automatic habit.