Metric measurements?

[Dan]

Seems right, even if I'd do the math a little different and in steps:

• 12 L/min @ surface = 12/15=0.8 bar/min @ surface
• @ 30M (4 barA), that's 0.8*4=3.2 bar/min (a really nice number to have, because you can use it to monitor if your gas consumption is what you planned for. "10 minutes bottom time should be about 30 bar")
• 200 bar / 3.2 bar/min = 62.5 min

I'd recommend ascending a little before that, though No matter whether you use metric or Imperial...


Now let me do a quick min gas calculation using those numbers:

Time at depth to sort out the issues: 1 min @ 30M, 4 barA
12 lpm @ surface = 48 lpm @ 4 barA. Round to 50. Times one minute is 50L.

Ascent: 10 m/min, average dept: 15m, average pressure: 2.5 barA
12 lpm @ surface = 30 lpm @ 2.5 barA. Times 3 minutes ascent time is 90L.

Safety stop: 3 min @5m, 1.5 barA.
12 lpm @ surface = 18 lpm @ 1.5 barA. Round to 20. Times 3 minutes is 60L.

90+60+50=200L. Plus buddy is 400L. Times two for stress is 800L. Divide by 15L/bar is 53 bar, round to 60. Add 10 bar to ensure a working 1st, and your min gas tank pressure @ 30M is 70 bar. A little less if you're willing to skip the SS if SHTF.

So considering min gas your available bottom time goes from 62.5 min to (200-70)/3.2 = 41 min. Still a bit excessive to me, even on EAN32 Which is probably the reason I've only seen 12L 200 bar tanks when I'm vacation diving.

This is a very good, easy to estimate, gas planning calculation. Thank you for posting it!

Yes, I do the same. I dive NDL. Tank size is no longer the limiting factor. Bottom time is.

 

[Storker]

I dive NDL. Tank size is no longer the limiting factor. Bottom time is.

If I'm on air, my NDL and my min gas time are very similar in the deeper (for me) range, since I'm using between 15 and 20 lpm. On vacation, in a wetsuit, I normally breathe some 12-15 lpm, so the pretty standard 12Lx200bar is enough for me.

On 32%, I'm always gas limited even if my tanks are 10Lx300 bar with an effective gas capacity of some 2700 surface liters. But it's all good because I generally want to get out of the water to take a leak when my run time is around an hour.

 

[Storker]

This is a very good, easy to estimate, gas planning calculation. Thank you for posting it!

My pleasure.

Another trick I'm using is to aim for round numbers. It makes the mental arithmetic a lot easier.

My gas consumption rate in my home water, in my drysuit, is consistently between 15 and 20 lpm with only a few outliers. All my tanks are 10L, so I'm using 20 lpm (i.e. 2 bar/min) in my gas calculations, am aware that it's probably close to worst case and subtract up to 25% from the final numbers. If my tanks were 15L, I'd use 15 lpm (1 bar/min), remember that it's close to a best case and add up to 30% to the final numbers. For 12L tanks, I'd use 18 lpm (1.5 bar/min), giving me a pretty nice middle-of-the-road scenario.

That'd give me the following estimates for 10 min @ 30m:

• 10L tank: 2*4=8 bar/min; in 10 min I'll use between 80 bar and 60 bar
• 12L tank: 1.5*4=6 bar/min; in 10 min I'll use around 60 bar, plusminus perhaps 10-15 bar
• 15L tank: 1*4=4 bar/min; in 10 min I'll use between 40 bar and 55 bar

This approach can of course be used for min gas estimates as well.

 

[Miyaru]

How is the EADD expressed in the imperial system?
Pounds per gallon? Stones per cubic feet?