Is my air consumption...bad-ish?

[Kimela]

Is there an EASY way to calculate my air consumption - without having to do calculus (or whatever branch of math is involved)? When I was using my Datamask, and the software was still supported, I could access it via my computer. But now I'd have to figure it out on my own and ... er ... I'm lazy? (So sorry if this question has been asked and answered a zillion times already)

 

[Kmart921]

Is there an EASY way to calculate my air consumption - without having to do calculus (or whatever branch of math is involved)? When I was using my Datamask, and the software was still supported, I could access it via my computer. But now I'd have to figure it out on my own and ... er ... I'm lazy? (So sorry if this question has been asked and answered a zillion times already)

The easiest way is of course an air-integrated dive computer like a Perdix AI, which gives you real-time data. Although it will give you the SAC rate in psi/min, so you will still have to do a little math to convert it to RMV (as it will depend on your tank size).

Otherwise you can calculate it using your average depth, gas used, and dive time. Say you used 2500 psi in an AL80 over 60 minutes at an average depth of 40ft. That's 2500 psi x 77.6cuft/3000psi (capacity of an AL80 at rated pressure) = 64.6cuft of gas. Then divide that by your average depth in atm, then by dive time to figure out how much gas you would have used on the surface. 64.6cuft / ((40/33)+1) = 29.2cuft / 60min = 0.48cuft/min. That would be your RMV. Which actually is basically what the OP has!

 

[scubadada]

Hi @Kimela

Sorry to hear about your Datamask. There are a number of SAC/RMV calculators available online, here is one of them DiveBuddy Enter your average depth, dive time, gas used, and cylinder characteristics and you will get your SAC and RMV. This one will not allow you to use 77.4 or 77.6 cu ft for an AL80, but you can use 77 or 78 cu ft if you want, the differences are modest

 

[outofofficebrb]

The easiest way is of course an air-integrated dive computer like a Perdix AI, which gives you real-time data. Although it will give you the SAC rate in psi/min, so you will still have to do a little math to convert it to RMV (as it will depend on your tank size).

Otherwise you can calculate it using your average depth, gas used, and dive time. Say you used 2500 psi in an AL80 over 60 minutes at an average depth of 40ft. That's 2500 psi x 77.6cuft/3000psi (capacity of an AL80 at rated pressure) = 64.6cuft of gas. Then divide that by your average depth in atm, then by dive time to figure out how much gas you would have used on the surface. 64.6cuft / ((40/33)+1) = 29.2cuft / 60min = 0.48cuft/min. That would be your RMV. Which actually is basically what the OP has!

It is no secret that I am horrible at math and bring much dishonor to my Asian family LOL. An online calculator that I can just fill in boxes with automagical workings sounds more like my jam. Thanks for explaining the math. I'll have to take a peek and see where I'm at. I have good SAC data from AI but am curious about RMV.

 

[stepfen]

Is there an EASY way to calculate my air consumption - without having to do calculus (or whatever branch of math is involved)? When I was using my Datamask, and the software was still supported, I could access it via my computer. But now I'd have to figure it out on my own and ... er ... I'm lazy? (So sorry if this question has been asked and answered a zillion times already)

Subsurface is a very popular option for this. Once you import the dive(s) from your computer, you key in your tank size together with start and end pressures and the software calculates consumption. You just need to remember those 3 numbers (tank size, start and end pressure).

Easier than this, you'd need an air integrated computer.

 

[Lorenzoid]

. . .
Another possibility to consider is that those divers that come up 10 minutes after you are spending longer at their safety stop and coming up with less reserve. . . .

I have long had my suspicion that this occurs. I like to err on the conservative side and surface with what my SPG tells me is at least 500 psi, because the idea of maintaining a safety margin has been beaten into me, not to mention that the accuracy of SPGs may be less than perfect, and regs may start to behave funny when the pressure gets really low. My average SAC is around 0.5-0.6. I am often one of the first to surface. And so long as I had a good dive, I don't care.

 

[GreggS]

Subsurface is a very popular option for this. Once you import the dive(s) from your computer, you key in your tank size together with start and end pressures and the software calculates consumption. You just need to remember those 3 numbers (tank size, start and end pressure).

Easier than this, you'd need an air integrated computer.

This is what I was going to suggest had you not already. It's a very simple thing to input the info. In fact, you can specify the tank size you normally use in settings so it will automatically enter that. You can change it if you do use a different sized tank. I have AL80 as my default, but I sometimes use a steel 100HP so I just change it manually for those dives. Then all you have to do is input the start and end pressures.

 

[GreggS]

Duplicate post.

 

[scubadada]

It is no secret that I am horrible at math and bring much dishonor to my Asian family LOL. An online calculator that I can just fill in boxes with automagical workings sounds more like my jam. Thanks for explaining the math. I'll have to take a peek and see where I'm at. I have good SAC data from AI but am curious about RMV.

If you have your SAC from your SW computer, all you have to do is multiply by the tank characteristics to get your RMV.

For a HP100: 13 psi/min * 100 cu ft/3442 psi = 0.38 cu ft/min

 

[outofofficebrb]

If you have your SAC from your SW computer, all you have to do is multiply by the tank characteristics to get your RMV.

For a HP100: 13 psi/min * 100 cu ft/3442 psi = 0.38 cu ft/min

Thanks - I also just realized (duh...) that MacDive calculates both SAC and RMV for me so I'm good. Whew!