Air consumption

[Storker]

it was probably on your DM course that you first heard of Boyle's Law/Mariotte's law.

I'm a scientist, and frankly, I probably couldn't quote neither Boyle nor Mariotte even at gunpoint. OTOH, I can give you the ideal gas law (PV=nRT) in my sleep and with a BAC above the driving limit in any country that cares about stuff like that. And with the ideal gas law, you don't need to be arsed with Boyle, Mariotte or any other of the subsets.

Point is, as long as you know the equation, you don't need those names.


--
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Typos are a feature, not a bug

 

[danvolker]

You're breathing compressed air, at 10 metres you're getting twice the oxygen. The limiting factor is how much oxygen gets from the lungs to the muscles and in trained athletes that number is "a lot, compared to a regular bloke". And it doesn't matter anyway unless you're trying to outswim a shark uphill and against the wind...

Agreed with the O2
Also an issue...is getting rid of CO2....an elite athlete will get rid of CO2 much better than a non-athlete.....First sign of not getting rid of CO2 fast enough, beyond the very fast breathing rate.... is a serious headache
The deeper you go past 90 feet, the more dramatic the issue of getting rid of CO2 with high exertion, becomes.

 

[The Chairman]

Dear OP,

You're asking us to do the impossible: diagnose your heavy breathing with absolutely nothing to go on. Might as well ask a blind person to criticize a painting. Or maybe ask a deaf person to evaluate a concerto.

Post a video for us. Come down to the Keys and let's go for a dive. Or find another mentor that can actually see and evaluate your dive first hand. Then you'll get some pertinent advice.

My number one tip to my AOW students: stop using your hands! Sculling takes energy and produces scads of CO₂. Most students improve their SAC simply by doing this. In fact, a lot of people who think they have excellent buoyancy, have this horrible habit. They are actually compensating for sub standard trim and buoyancy with their sculling. I'm not saying you do or don't, because frankly, I haven't seen you dive. All I can do at this point is to guess.

FWIW, I am obese. Some would say morbidly so. My average SAC is 0.4ish. Sometimes a bit under. Sometimes a bit over. I Zen under the water. I am totally relaxed, kick slowly and am about the laziest diver you'll ever hope to meet. Probably why I'm obese.

 

[ajduplessis]

I know of a OOA diver with a SAC of 0.0, try and beat that!

 

[scubadada]

It sounds like you would be a prime candidate for a GUE Fundys class. My SAC rate was around .8 and now it gets as low as .16 on certain dives.

.16, really?

So if I did the math correctly -

RMV = ((PSI Used / Working Pressure) x Cylinder Capacity) / (((Depth / 33) + 1) x Minutes)
.16 =((1600/3000)*77.4)/(((200/33)+1)*35)

Did I get that right? You used 1600 psi of an AL80 at 200 feet for 35 mins for an RMV of .16?
I have been thinking about this one for awhile - that is either tremendous or I must not understand correctly.

I find those numbers extremely startling. In the last five or six years, I have dived with one person who routinely outlasts me on gas, and his SAC rate is in the high .2's.

All I can say is, really? I do reasonably well, my average SRMV for the last nearly 600 dives is 0.37, my best is 0.27 cu ft/min. It is very difficult to comprehend a 0.16. I wish Nemrod would deign to share his SRMV with us, rather than taunting us, to put this into some kind of perspective. I'm thinking 0.16 is impossibly low.

 

[boulderjohn]

All I can say is, really? I do reasonably well, my average SMRV for the last nearly 600 dives is 0.37, my best is 0.27 cu ft/min. It is very difficult to comprehend a 0.16. I wish Nemrod would deign to share his SMRV with us, rather than taunting us, to put this into some kind of perspective. I'm thinking 0.16 is impossibly low.

It is significantly lower than what Edd Sorenson told me his was when we were planning dives, and I was pretty impressed with Edd's.

 

[scubadada]

We're talking about a real "dive" with an SRMV of 0.16

 

[danvolker]

While I think it would extraordinarily stupid to do this....I would imagine you could skip breath at 200 feet deep, and as long as your system could flush the CO2 with your ventilation abilities....assuming high aerobic fitness, and a large buffering system in place from aerobic training...bicarbonate buffering, phosphate buffering and muscle based....you might manage to slow heart rate to minimal resting levels as low as 50 or 60 ( or lower in some people), and doing nothing on the dive much beyond drifting like plankton ..... with the skip breathing, you might just get the O2 to go a lot farther than it would on a 30 foot deep dive....so you might be able to create an artificially low and kind of ridiculously unusable SAC Rate even below .16

It would also be a great way to tox on air, and be a great way to waste the adventure potential of a deep dive.

...I would go with a rebreather a long time before I would consider this!!!

 

[JohnN]

While I think it would extraordinarily stupid to do this....I would imagine you could skip breath at 200 feet deep, and as long as your system could flush the CO2 with your ventilation abilities....assuming high aerobic fitness, and a large buffering system in place from aerobic training...bicarbonate buffering, phosphate buffering and muscle based....you might manage to slow heart rate to minimal resting levels as low as 50 or 60 ( or lower in some people), and doing nothing on the dive much beyond drifting like plankton ..... with the skip breathing, you might just get the O2 to go a lot farther than it would on a 30 foot deep dive....so you might be able to create an artificially low and kind of ridiculously unusable SAC Rate even below .16

It would also be a great way to tox on air, and be a great way to waste the adventure potential of a deep dive.

...I would go with a rebreather a long time before I would consider this!!!

Plus if you breathing air at 200' you're going to be narked out of your mind (and facing about 78 minutes of deco if you're really at depth for 35 minutes)

 

[danvolker]

I would add that for deep diving, using a scooter makes great sense for allowing an ultra low heart rate, and related low breathing rate--without forcing you into the exertion levels of a phyto-plankton .... you get to see everything and cover lots of ground.