Average Gas Consumption

[Blackcrusader]

There appears to be an uptick in the number of views for this thread due to the @rsingler great thread on Rock Bottom calculations Why Surface with 500 PSI? Good reason to start calculating your RMV, if you do not already do so. Ten more votes in the poll since its birthday, 437 now

 

[Centrals]

In tropical warm water and using Al 80 my average SAC is 6-8L per min.

 

[Dan]

Just came back from Malpelo with @scubadada last week. He went over this SAC & RMV with me there. We did 18 dives. Our average depth was about 60 ft (18m). My RMV was 0.4 cfm (11 L/min).

Looking back, I would have saved $10/day of renting 15L tank and stick with free of charge AL80 (11L tank) as my return tank pressures of the 15L tank were mostly over 1000 psig and I carried 3cft Spare Air, which was charged to 3000 psig (207 bar) and never used it then, but it’s good insurance & peace of mind to have it.

 

[scubadada]

In tropical warm water and using Al 80 my average SAC is 6-8L per min.

You must be one of the 5 divers who voted less than 0.3 cu ft/min in the poll. Six to 8 L/min would be 0.21-0.28 cu ft/min. The lower part of that range appears to be pushing the lower limit for RMV Average Gas Consumption

For my last 1590 dives, my average RMV is 0.36 cu ft/min. The lowest I've ever had was just a shade under 0.27 cu ft.min

Just came back from Malpelo with @scubadada last week. He went over this SAC & RMV with me there. We did 18 dives. Our average depth was about 60 ft (18m). My RMV was 0.4 cfm (11 L/min).

Looking back, I would have saved $10/day of renting 15L tank and stick with free of charge AL80 (11L tank) as my return tank pressures of the 15L tank were mostly over 1000 psig and I carried 3cft Spare Air, which was charged to 3000 psig (207 bar) and never used it then, but it’s good insurance & peace of mind to have it.

Hi Dan, that was really a great trip, your video is fantastic I will be posting my review in the next few days

Despite the current, surge, thermoclines, changing visibility, and, of course, all the excitement, my RMV was below my average of 0.36 cu ft/min. For our 18 dives the avg was 0.33 cu ft/min (0.31-0.38).

I really enjoyed our conversations regarding SAC/RMV and the inner workings of our Teric computers. I'm hoping others will calculate their gas consumption when they discover it is as simple as multiplying the SAC (calculated by Shearwater computers) by the tank factor. For your AL100, it is 100/3300 or 0.030 cu ft/psi. For my AL80, it is 77.4/3000 or 0.258 cu ft/psi.

 

[Dan]

For your AL100, it is 100/3300 or 0.030 cu ft/psi. For my AL80, it is 77.4/3000 or 0.258 cu ft/psi.

I’ve been using the tank factor of 100/3000 or 0.0333 cft/psi. So, my actual RMV is < 0.4 cfm then.

The 75F (24C) at 114.5’ (35m) deep dive’s excitement of watching the Galapagos Shark parade was sure messed up my RMV. LOL

 

[rsingler]

@Dan , I think you are correct. The 10% overpressure for calculations only applies to LP steel tanks, AFAIK.
For a 300psi AL tank the correct denominator is 3000. But you might also confirm the actual capacity from the mfr. Some are like 102 or 204 cu ft.

 

[tursiops]

@Dan , I think you are correct. The 10% overpressure for calculations only applies to LP steel tanks, AFAIK.
For a 300psi AL tank the correct denominator is 3000. But you might also confirm the actual capacity from the mfr. Some are like 102 or 204 cu ft.

I thought all AL100s were 3300 psi.

 

[rsingler]

I thought all AL100s were 3300 psi.

If that's the working tank pressure marked on the neck...

 

[scubadada]

I thought all AL100s were 3300 psi.

I thought so too

 

[uncfnp]

Just came back from Malpelo with @scubadada last week. He went over this SAC & RMV with me there. We did 18 dives. Our average depth was about 60 ft (18m). My RMV was 0.4 cfm (11 L/min).

Looking back, I would have saved $10/day of renting 15L tank and stick with free of charge AL80 (11L tank) as my return tank pressures of the 15L tank were mostly over 1000 psig and I carried 3cft Spare Air, which was charged to 3000 psig (207 bar) and never used it then, but it’s good insurance & peace of mind to have it.

In Socorro I paid up for the steel 12 L which isn’t that much additional gas. For me it is more about the characteristics of the tank, shorter than the al 80 and lets me take about 4 lbs or so off my weight belt.