13 Cu. Pony Tank

[markfm]

The SPG is kind of important, for me. I do run with it on all the time, and practice, so need to top it off periodically.

Ease of valve access is why, given that I am content with a tank mount, I have it inverted. On vacation I had a minor reg leak that I couldn't get repaired on site, so dove with the hose charged, but the valve turned off.

 

[TheRedHead]

Here's 1.0 cu ft / min (excited) breathing with 1 min at depth, a 30 fpm ascent rate and 3 min @ 15' stop:

Has anyone ever calculated their most excited breathing rate? My worst was 0.65 on a dive where I almost blew out my eardrum with a reverse block. I have downloaded all my dives from my computer and I consistently breathe 0.35-0.45 cu ft/min on most of my dives.

 

[BigTuna]

Am thinking about purchasing a 13cu. Pony tank. Does anyone have any comments on this size tank as reserve air.

As others have already said, it depends on whether the pony has enough gas for your ascent. I looked into this in connection with "Rock Bottom" calculations and found the attached spreadsheet on the board. Just set up the pressure and volumes for tanks you're considering, and enter the type of ascent you'd likely use.

Here are some results using 1 cf/min as your nominal Surface Air Consumption (SAC) rate. A 13 cf pony with a true pressure of 3000 psi would get you to the surface from about 70 feet, and a 19 cf pony with 3000 psi would get you up from about 110 feet. These ascents are assumed to have a minute for sorting things out at depth, a controlled, 30 fps ascent rate, a 3 minute safety stop, and a 300 psi "pad," or safety margin.

You can play with the ascent parameters and look at the tank pressures and volumes for various depths to figure out what works for you.

A bonus is that the spreadsheet teaches you how easy it is to make your own gas requirement calculations. And needing the answers underscores the importance of knowing your personal SAC.

PS--Anybody know who made this spreadsheet? Thanks, whoever you are!

 

[lamont]

Has anyone ever calculated their most excited breathing rate? My worst was 0.65 on a dive where I almost blew out my eardrum with a reverse block. I have downloaded all my dives from my computer and I consistently breathe 0.35-0.45 cu ft/min on most of my dives.

I *averaged* 1.1 cu ft / min over a 30 min dive back when my dives were in the single digits. And I wasn't scared of dying, I just wasn't used to diving and soupy viz yet...

My typical rate is more like 0.6 cu ft / min. I'm male and 195 lbs.

 

[BigTuna]

Has anyone ever calculated their most excited breathing rate? My worst was 0.65 on a dive where I almost blew out my eardrum with a reverse block. I have downloaded all my dives from my computer and I consistently breathe 0.35-0.45 cu ft/min on most of my dives.

For comparison, sitting on the sand at 30 feet for 5 minutes, I computed my SAC rate to be about 0.5/min. When I'm swimming relaxed with no stress, I seem to be between 0.6 and 0.8. With any expenditure of effort, I'm around 1!

Any thoughts as to why my numbers are so high? Big lungs, maybe? Or why yours are so low?

 

[mnj1233]

Minimum 19cf. IMO depends on your dive profile.

 

[TheRedHead]

For comparison, sitting on the sand at 30 feet for 5 minutes, I computed my SAC rate to be about 0.5/min. When I'm swimming relaxed with no stress, I seem to be between 0.6 and 0.8. With any expenditure of effort, I'm around 1!

Any thoughts as to why my numbers are so high? Big lungs, maybe? Or why yours are so low?

Women typically have lower gas consumption than men because we have smaller lungs. I know a tiny female DM in Florida who makes 2 dives on an AL 63, shallow of course. I'm not small (5'10 and 150 lbs), but it is an advantage that women have in diving. I typically dive with a Steel 100 and my male buddy dives with a 120 and I always have 200-300 psi more than him at the end of the dive.

 

[ProfessorAronnax]

Oh, they're fine - just as long as you carry a redundant needle. Unless you're into one of those closed-circuit sergers in which case don't get me started.

Sorry, It still scares the heck out of me!

 

[cebudiver]

I dont really know some of the calculations being done here, so here is another question on the same topic. How long will a 13 cu. last me at 20ft breathing calmy at say 25-30 breathes a minute. Will is suffice to do a 20 minute deco at 10 at 25 breathes per minute? Please dont ask why a deco like that would be necessary this is just a more practical analysis than going out of air at 100ft.

 

[doole]

I dont really know some of the calculations being done here, so here is another question on the same topic. How long will a 13 cu. last me at 20ft breathing calmy at say 25-30 breathes a minute. Will is suffice to do a 20 minute deco at 10 at 25 breathes per minute? Please dont ask why a deco like that would be necessary this is just a more practical analysis than going out of air at 100ft.

There's a missing variable, here. First, you have to measure your breathing rate at the surface, (everyone is a little different) THEN factor in how much that volume of air is compressed at, in your example, 20 ft.

Also, it makes a difference how relaxed you are.