Quick Reference: SAC & RMV Chart

[dewdropsonrosa]

I'm brushing up on my gas planning math in preparation for my next cave diving trip (coming up in two weeks!). To save some space in my Wet Notes/not need to calculate consumption de novo for each dive, I made a chart of RMV for depths of 20-200ft at SAC rates of 0.4, 0.6, 0.8, 1.0, 1.5, and 2.0 cfm.

Click here to open the chart in Google Drive for download.

The values were derived by formula and then rounded off to two digits in Excel, so things are not microscopically exact but are going to be within mere hundredths of an atmosphere.

(And now I see the typo on the 95-foot line.)

 

[tbone1004]

out of curiosity, and I'm an engineer, so I'm prone to the same, but why go to hundreths instead of tenths, and why in 5ft increments?

 

[dewdropsonrosa]

Extra rows and digits are a nice distraction from the howling black void of being done with grad school but not having heard back about my most recent job interview yet!

 

[tbone1004]

Extra rows and digits are a nice distraction from the howling black void of being done with grad school but not having heard back about my most recent job interview yet!

If I were you....
A. formula is 34 not 33 since the caves are freshwater
Y-axis change to 10ft increments
X-axis, that one do 0.4, 0.5, 0.6, 0.7, 0.8, 1.0. You'll never see above that or plan above that
Values-change from depth air consumption rates to psi/min and make multiple tables for your common tanks. For me that would be AL80's, HP120's, and HP149's and that way you can reference your psi/min consumption and convert that back to your SAC rate.

Makes the values more useful in the water, tables easier to read, and helps with gas planning.

 

[dewdropsonrosa]

My logic for including 1.5 and 2.0 is for emergencies/air-sharing situations.

(I've also been known to blow a 0.95 in Ginnie when I have not done enough cardio prep for a trip, but my personal failings don't need to be recorded in the chart...)

 

[kensuf]

Just switch to metric and be done with it.

RMV @ 0m = 14L
RMV @ 3m = 1.3x14L
RMV @ 6m = 1.6x14L
RMV @ 9m = 1.9x14L
RMV @ 12m = 2.2x14L
....
RMV @ 80m = 9.0 x 14L

 

[dewdropsonrosa]

That's a very compelling argument after the amount of time I spent working on the PSI conversions for a bunch of different tanks yesterday.

 

[kensuf]

I hear ya', I'm still very much stuck in the imperial world. Growing up, I had the privilege of living in Canada when they first went metric, then moved back to the states which was in process to go metric, then to an island that had "imperial gallons" (5 qt instead of 4) and then back to the states. The transitions for me were imperial -> metric -> imperial -> quasi-metric -> imperial imperial -> imperial. I'm all kinds of messed up when it comes to anything useful involving grams, ounces, quarts, fahrenheit and celsius. Meters/Feet/Kilometers/Miles I have a good handle on, pounds and kilos I also have under control, and I truly do enjoy a nice cold pint every now and then.

 

[lowwall]

and I truly do enjoy a nice cold pint every now and then.

Is that the 473.18ml US pint or the 568.26ml UK one?

 

[-JD-]

... and I truly do enjoy a nice cold pint every now and then.

Is that an imperial pint or an Imperial pint? I can't tell you how many my uncle sent back because instead of scraping the head and filling to the top here, they fill the head to the top and let it settle. Always felt like he was being cheated hear after touring the UK. Poor wait staff ...