Breathing and buoyancy

[Thanshin]

This question is quite long and boring. Also, what I'm about to say is based on much thought and little experience (I have more thinking time than diving time).

I'll start with the premises:
- Air in your lungs gives you an acceleration towards the surface.
- You shouldn't stop breathing.
- The objective is to stay as stable as possible.

Considering only the acceleration produced from air in your lungs, the position is equal to 1/2at. Thus, it will be in direct proportion to the amount of air in your lungs and the time it spends there.

So, to keep the position stable between respirations, we must create the same amount of (a*t) up as down. To reach this "amount" we can just integrate the breathing cycle function.

However, that function can have the position of equilibrium at any point in the lungs fill range. Giving endless different possibilities of achieving a perfect balance.

Let's say the lungs fill from 0 to 10.

You could set the neutral buoyancy at 8 and then keep:
- A symetric breathing cycle ranging from 6 to 10.
- A breathing with a longer exhalation(sp?) time, moving between 4 and 10.
- Or even a cycle that has a long, slow exhalation and an inhale that starts strong and then starts slowing down after passing the neutral buoyancy point; ranging from 0 to 10.

Alternatively, you could set the neutral buoyancy at 2, and reverse the full and empty times, or set it at 5 and keep a symetric breathing cycle from 0-10, 2-8 or whatever.


And now, for those still with me, the questions:

- Where do you set the neutral buoyancy point and what cycle do you usually keep?
- Do you change the point during the immersion or you purposefully "touch" your BC to reposition your neutral buoyancy in the same spot after a depth change.

Before answering, take into account this question is about buoyancy, not about saving air. My opinion on that is that breathing patter has little influence on air expenditure, but I'd rather discuss that in another thread anyway.

 

[BonaireDan]

Good points but yes, a bit confusing and complicated. Once you have gotten to depth, whatever that is you establish neutral buoyancy with weights and air in you BC (if appropriate). Now you must breath of course. Normal breathing - depth (volume) and rate will maintain that buoyancy. Remember that things happen slowly in the water (usually) like you found doing a fin pivot.

It is mostly an art rather than a science. Practice will perfect the buoyancy aspect of your diving.

I am sure others will have far better comments than mine.

 

[dkktsunami]

Way over thinking this thing.

 

[gypsyjim]

Not sure I am answering your question, but can speak for myself only.

I have my buoyancy established for my normal breathing pattern. In warmer waters when in a skin or shorty, after venting BC to descend I make no adjustments until I have reached the surface again and add air for buoyancy there. In colder waters the wet suit does require some adjustments at depth due to compression of the material, but the concept remains the same.

At all depths 100' to surface I use lung volumes to control my depth adjustments. Take a deeper breath, and then breath off the top of my lungs, and I will begin to rise. I then return to a normal pattern to maintain my depth. The reverse works when I wish to drop, exhaling deeply and then breathing off the bottom of the lungs causes me to begin to drop deeper. Uneven terrain is fun to navigate this way, using only your lung volume and breath control to "fly" threw the ups and downs!

I hope this is at least a part of the answer you were looking for.

 

[Steve50]

First sentence is very accurate...

 

[Solly]

depth will affect your analysis, when you breath near the surface the volume of your lungs are large as there is not a lot of pressure around hence your analysis about breathing and buoyancy is correct, however once you get deeper, your lung volume change with breathing will not have that effect over your buoyancy.
That is why when diving shallow you can dispense with your BCD inflating/deflating action and just use your lung volume to control your depth, however once you get to below 15m (in my case) I have to use the BCD to control my buoyancy.

 

[diver 85]

Way over thinking this thing.

I'm thinking he has a speedometer on his vehicle that registers in hundreths-----"man, I'm doing 68.663 MPH....."


To the OP, just dive & all this will become a lot clearer.....

 

[DevonDiver]

I noticed the biggest improvements in air consumption and fine buoyancy when I just stopped thinking about my breathing and just did it naturally.

 

[gypsyjim]

Well said Devon, but that is the difference between op's 0-24 dives and your 2,500-4,999. Experience, it takes time to get to where things just seem to happen naturally.

 

[ScubaSteve]

With more experience, you will realize that worrying about breathing is actually counter-productive. Just breathe normally.....it is that simple. To establish neutral buoyancy, you add air to your BC (or let it out if your depth gets shallower) at depth (and and significant depth change that cannot be compensated for with your breathing) until such time as you are able to maintain that depth with only breathing normally. This should not be based on huge gasps for air just as it should not be based on you forcing every last ounce of breath from your lungs. Just breathe normally and don't try to apply a numeric value of 1-10. With experience, what is a 5 to you today may be a 3 tomorrow.....just breathe. Get experience and continue to learn (just as you are here).