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Z-factors still apply to tanks that are directly measured. I.e. 250bar 11L is not 250*11=2750L, it's 250*11/1.06=2600L
Diminishing Returns and Gas Calcs for Cave Filled LP Tanks?
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Z-factors still apply to tanks that are directly measured. I.e. 250bar 11L is not 250*11=2750L, it's 250*11/1.06=2600L
Oh I know, but since I don't dive a ccr or scooter I can ignore them (for everything except SAC swims) and be safer.
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no differently than we do on OC with indirect measurements, though I can't disagree that direct is easier.
I was just thinking the same, our American cousins really like to make life difficult.
In fairness, I guess it has lot to do with what you know. But every time I see an American calculating available gas, breathing rates etc it blows my mind how complicated it is.
KevinNM
Contributor
Luckily they sell bar gauges in the US.
helodriver87
Contributor
I was just thinking the same, our American cousins really like to make life difficult.
In fairness, I guess it has lot to do with what you know. But every time I see an American calculating available gas, breathing rates etc it blows my mind how complicated it is.
It's definitely more complicated, but it's like being fluent in a slightly illogical language (like English). It's just how your brain thinks. I can work in metric, but I end up converting it to units I'm familiar with to contextualize it. Which totally defeats the purpose. So while there are a few extra steps, I can calculate gas volumes, bailout, turn pressure with dissimilar tanks, etc in my head pretty quickly. And I see no reason to mess with a process that works.
I can understand that.
I am part of the 'decimalisation generation' - when I would normally have been learning pounds, shilling and pence, imperial weights and distance etc, they where teaching me the decimal equivalent.
For years, into my 40's I struggled with visualising volume, and weight. Funnily enough it was diving that finally made it understandable.
I am also fo the generation that uses inches and mm's.
So something may need to be an inch or so in diameter +/- a few mm, and a foot or so long, +/-5mm
That makes no sense to Europeans, or Americans, but perfectly obvious to my generation.
Same here. Although metric could in principle be simpler, divers tend to muck it up using water volume when they're talking about how much gas fits in a tank. That tends to make the metric calculations divers use a little shifty. I could get used to talking about gas volume in cubic meters pretty easily but nobody else does that so it's pointless.
It seems so arcane!
Metric's so simple. Liquid volume (in litres) X pressure (in bar) = standard gas volume (in litres at sea level)
This is particularly important if you get a good / bad / mean as hell fill, or even recalculating if you've a partially used tank.
What matters is what you've got, not what's stamped on the tank as fed by some marketing gimp.
Thus an "Ali80" is 11 litres (actually 11.1, but who cares about the .1). So if you've a part used one with 150 bar, it's 11 X 150 = 1,650 litres of gas. Or a full one is 11 X 208 = 2,288 litres. Or a mega cave filled one is 11 X 230 = 2,530. Obviously temperature counts.
I do pity you for having such complex arithmetic to calculate something that should be so simple.
helodriver87
Contributor
It's really not bad. Say I'm 1000ft from the door at 110' and want to figure out a new usable gas volume to set turn pressure for a detour. 1000ft is about 30min swimming, conservatively. Assuming I'm sharing, I'll double my stressed rate of .75 to get 1.5 cubic ft/min. I know it's about .3ATA per 10 ft plus surface ATA, so that's 4.3 x 1.5. Call it 6.5 combined scr at depth (rounding is your friend). Times 30 is 195 cubic ft. Tank factors simplify things a lot and you only have to remember a few numbers. If I'm using 104s, that's 8. Divide it into 195 and you get 24 and change. Just round it up. Add on a couple zeros and you have your reserve, 2500. Divide your remaining gas by three and subtract from current pressure and you've got turn. All doable in your head within a minute or two with practice. It would take me significantly longer to get there in metric and I'd probably make mistakes. It's just about fluency.
