Buoyancy and Breathing

[MauiScubaSteve]

From my understanding, the only way to avoid some variation in buoyancy when breathing is to get a rebreather.

Technically, the counter-lung would have to be at the same exact depth as the lungs for there to be no shift in buoyancy. Since the counter-lungs are typically not at the same depth as the lungs there is a slight change in buoyancy for the entire "system," but definitely not nearly as much shift as with scuba.

 

[Akimbo]

Technically, the counter-lung would have to be at the same exact depth as the lungs for there to be no shift in buoyancy. Since the counter-lungs are typically not at the same depth as the lungs there is a slight change in buoyancy for the entire "system," but definitely not nearly as much shift as with scuba.

Technically true, but even in 10' of water I could never detect any variation diving rebreathers. In deep water the volume change in 6" of water due to compression would be difficult to measure let alone perceive. After the lower noise and warmer gas, the absence of buoyancy change during a breathing cycles was the most striking thing about using a rebreather.

 

[Herk_Man]

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.

The Jaws theme would be a good one. Would be a good rate of exhalation too I would think.

 

[Herk_Man]

Akimbo, I completely agree with you. I'll explain my reasoning, although with the note that I now see my original reasoning as ridiculous. I was considering my breath to be (say) 5# and my BC to be 20#, therefore my breath made up 20% of my buoyancy. With 30# in my BC, my breath would only be 15%. However, as you point out, my float/sink rate is dependent on the buoyancy change in real pounds. Thanks for the detailed rebuttal; when I read it I felt pretty dumb.

And yeah, I'm breathing less and deeper and not getting thrown into rocks as much as I was 20 dives ago. I've still got a long way to go though.

The explanation in the link that TS&M provided is the best one I've seen. And it doesn't contain any voodoo solutions like a couple I've seen in this thread.

 

[aquaregia]

Tried a bunch of the tips this weekend; I was able to keep significantly more steady and my SAC didn't increase appreciably. Cheers!

 

[TSandM]

Glad to hear we were helpful!

 

[ajduplessis]

elan:

Try to breath with your diaphragm (yoga/martial arts style). Generally divers to try to expand their chest with "deep" breathing leading to big fluctuation in buoyancy. When using the diaphragm (breathing with the stomach) the lungs “expand” into the abdominal cavity, resulting in more controlled breathing and better buoyancy. I hope this explanation made any sense.

In fact it does not No matter how you breath (diaphragm or chest) the volume of the body and thus your buoyancy will change the same way.

I said more controlled breathing results in better buoyancy! Is this incorrect?

 

[Herk_Man]

What he was saying, aj, is that it doesn't matter how you breathe in regards to "where the air goes", the effect on your buoyancy will be the same. Air is air, whether you put it in your chest or your toe doesn't matter. And you can't put it anywhere other than your lungs anyway.

The thing that improves buoyancy when talking about breathing is the timing of the breath in relation to your inertia in the water column.

 

[Akimbo]

Akimbo, I completely agree with you. ... Thanks for the detailed rebuttal; when I read it I felt pretty dumb...

I just caught the above part of your post. I apologize; that was certainly not my intent.

 

[aquaregia]

I just caught the above part of your post. I apologize; that was certainly not my intent.

Hehe, no apology needed at all! Perhaps I should have said "When I read it I felt happily enlightened."