1/3 Rule?

[fnfalman]

Okay, now I have swallowed a bottle of aspirin to remove this headache.

Is there any charts out there that will allow me to just glance at them instead of going through all these calculations. Now don't get me wrong I clearly understand the value of understanding these consumption rates. And allowances for stops and different breathing rates for both divers. But a chart would sure make ones life easier when all is said and done. An again thank you all for the great contributions,

John

Buy yourself an air integrated computer and let the idiot box calculates out how much bottom time you have based on your air consumption.

 

[Tigerman]

...
It is best to keep some pressure in the tank to prevent any possible contamination of the tank.
..

Yes, BUT... How much pressure do you actually need in your tank for nothing to be able to get into it at say 20 meters?
3 bar should do, lets say 5 just for good measures.. In other words, less than you want in the tank to be able to surface..

 

[jdg]

Do you have any data in your log books from previous dives? I'd be looking for:

*Average* Dive Depth
Start PSI
End PSI
Tank Type (AL80, LP95...)
Total Dive Time

If you have all of that for a few dives then we can use that to establish an RMV rate for planning.

Actually I have six dives from my computer if that would help. No air it was not attached.

An thanks I recorded the ending psi. and starting was always 2900-3100 psi

Thanks

 

[rongoodman]

Buy yourself an air integrated computer and let the idiot box calculates out how much bottom time you have based on your air consumption.

Even assuming that its calculations are correct, how does it know about the buddy you're sharing gas with?

 

[jdg]

Here are the files

View attachment Dive_2013-03-25-1027.pdfView attachment Dive_2013-03-25-1208.pdfView attachment Dive_2013-03-27-1040.pdfView attachment Dive_2013-03-27-1224.pdfView attachment Dive_2013-03-29-1039.pdfView attachment Dive_2013-03-29-1216.pdf

I am drinking the air but getting better. Currents were coming and going in these dives. But not noted. Hope to have AI next time so you can see better air consumption.

 

[jdg]

Buy yourself an air integrated computer and let the idiot box calculates out how much bottom time you have based on your air consumption.

I have a computer thanks, the question is more about actual safe bottom limits for you and a buddy. Something that never actually came up in my courses. Yes sharing air did but what about being down and low on air and you need to share?

 

[Tigerman]

Load the files from your computer into the appropriate computer program for it, add the in/out pressures and the program should give you the sac rates..

 

[chrpai]

Assuming your measurements are correct, I've attached a spreadsheet to help you understand the data.

View attachment AirConsumption.xls

It looks like this:

Avg Depth Time PSI Start PSI End PSI Used Service PSI Capacity CF Used Average ATA RMV
30 26 3200 800 2400 3000 77.5 62.0 1.91 1.25
29 32 2900 700 2200 3000 77.5 56.8 1.88 0.95
20 38 3000 500 2500 3000 77.5 64.6 1.61 1.06
19 43 3100 750 2350 3000 77.5 60.7 1.58 0.90
40 32 2900 650 2250 3000 77.5 58.1 2.21 0.82
38 41 3000 450 2550 3000 77.5 65.9 2.15 0.75


Average 0.95
Median 0.92
Min 0.75
Max 1.25

RMV is cubic feet per minute at the surface.

What were the conditions for these dives? How many dives do you have total? It looks like you are trending down but it's hard to say. If these are all the dives you have total it looks like you are settling down into the .75cf range which is pretty typical for new divers. Until you have a lot of data to prove that I'd probably estimate 1cf/min for your RMV for planning purposes. This means at 33fsw you'd use 2cf/min and so on...

Put another way, that's about 40psi per minute at the surface for an AL80. 80psi per minute at 33fsw and so on.

 

[jdg]

I only have about 12 dives now. The dives as you can see by the temp is tropical and the conditions what would be described as excellent. A little current with drifting and some going against mild currents (I did not log those events but I know i was sucking more air then).

The measurements are off my computer except the PSI start and end points. I did write them down after each dive.

An thank you for taking the time.

Regards,

John

 

[fnfalman]

Even assuming that its calculations are correct, how does it know about the buddy you're sharing gas with?

I didn't say that the idiot box will think for you.

---------- Post added April 29th, 2013 at 08:46 AM ----------

I have a computer thanks, the question is more about actual safe bottom limits for you and a buddy. Something that never actually came up in my courses. Yes sharing air did but what about being down and low on air and you need to share?

Then you will need to calculate out the way Kerumbo and others have said. Back in the days, it was part of dive planning.