Buoyancy by DAN

[lamont]

even the whole concept of "tank size by air capacity" is bizarre

quick, what is physically bigger: a 2640 psi 104 cu ft tank or 3500 psi 119 cu ft tank?

IIRC, its fairly easy in metric. you've got SAC rates in L/m, tank size in L (water volume), pressure in bars.

so total gas capacity = tank size * fill pressure

SAC rate * ata = L/m consumption rate at depth

SAC rate * ata * secs = L consumed at depth

L consumed at depth / tank size = pressure in ata for rock bottom

EXAMPLE:

so, i think 50 L / min is a reasonable elevated 2-person SAC rate (?). Doing rock bottom for a 7 minute ascent from 4 ata (30m) with 'average' depth of 2.5 ata on a 10L tank:

50 L / min * 2.5 ata * 7 secs = 875 L

875 L / 10L = 87 bar

where you guys really, really, really suck is that 87 bar works for all 10L tanks no matter what the fill pressure is. this value works for all 15L tanks:

875 L / 15L = 58 bar

 

[pwl]

quick, what is physically bigger: a 2640 psi 104 cu ft tank or 3500 psi 119 cu ft tank?

yah - my point exactly

875 L / 10L = 87 bar

where you guys really, really, really suck is that 87 bar works for all 10L tanks no matter what the fill pressure is. this value works for all 15L tanks:

875 L / 15L = 58 bar

don't understand the "really suck" bit? you mean US measure (cu ft for a rated pressure) sucks cos it's complex in comparison?


i dread to think what a 15L tank would look like - some kind of monster!

 

[Twiddles]

OMG my eyes my eyes!!! M-e-t-r-i-c runaway runaway eeeek :11doh:

 

[lamont]

don't understand the "really suck" bit? you mean US measure (cu ft for a rated pressure) sucks cos it's complex in comparison?

No, you guys really suck because its too easy for you... No need for you to memorize that an LP104 is the same as an HP130 or convert to "tank factors" (cu ft / psi) to get water volume measurements...

 

[lamont]

i dread to think what a 15L tank would look like - some kind of monster!

15L @ 241 bar is basically the same size (and pressure) as an american HP120/HP119/HP130. 15L @ 182 bar is close to the LP95/LP96/LP104 tanks.

12L @ 241 bar would be equivalent to an HP100 and 12L @ 182 bar is an LP80.

the american AL80 is a 206 bar 10.6L tank.

everything make sense?

 

[DandyDon]

One does not simply sticky things in scubaboard.

I missed that in the rules. Got a link? :silly:

 

[SkullDeformity]

It was ruled by Dandy Don that there shall be no stickies under any circumstances. Praise his glorious wisdom.