Average Gas Consumption

[Dan]

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

Well, I reviewed my Shearwater iCloud logbook to see the data for that deep dive. Actually it wasn’t messing up that badly. May be because we were just hanging still on the bottom, relaxing & enjoying the show. My SAC was 9 psi/min at 115.9’ depth, as shown, below.

The average SAC was 12.67 psi/min, as shown, below. I think the yoyo diving (from 60’ down to 80’, up to 60’, down to 80’, up to 50’, down to 70’), when was in the middle of schooling fishes (snapper, bonito tuna, bigeye jack) before the slow ascent to the surface, messing up my SAC.

 

[Blackcrusader]

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

Maybe it's the lazy dives we do in those tropical waters that lead to good sac rates. I do a lot of dives where we simply drift with the currents. Also the places I dive the guides are also excellent on air some are better than I am yet they never concern themselves with knowing their sac rate. Mostly I would be in the 8l min range on most dives.

 

[Dan]

Maybe it's the lazy dives we do in those tropical waters that lead to good sac rates. I do a lot of dives where we simply drift with the currents. Also the places I dive the guides are also excellent on air some are better than I am yet they never concern themselves with knowing their sac rate. Mostly I would be in the 8l min range on most dives.

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My 9 psi/min SAC in the above post at the bottom (35 msw) motionless, while watching the Shark parade is equivalent to 8 L/min RMV.

 

[scubadada]

I generally only report RMV for entire dives, fair way to balance the extremes.

 

[scubadada]

This thread recently passed 20,000 views, who would have thought? Twenty one more votes in the 2016 poll

 

[scubadada]

Answer to a previous question: Pelagic Pressure Systems/Oceanic... does not correct for deviations from the ideal gas law at higher fill pressures, see edit at bottom of this post New Shearwater AI transmitter - the Swift

 

[scubadada]

A few more votes in the 2016 poll since the last update. The topic of gas consumption and RMV comes up fairly frequently, like in this recent thread by @stuartv Info - Scootering and RMV Remember, you can change your vote in the poll if your average RMV has changed.

 

[scubadada]

Sometimes, the diving is very easy...

Over the last 1,654 dives, my average RMV is 0.36 +/- 0.04 cu ft/min (mean +/- std dev). I recently returned from a two week trip to Bonaire with my wife, where I did 45 dives Trip Report - Bonaire: Den Laman and Dive Friends, October 20-November 3, 2021. My average RMV was 0.32 +/- 0.03 cu ft/min. The water was warm, 83-5 degrees, the visibility was good, 50-100 feet, and there was generally little to no current.

I had my lowest RMV ever, more than 2 std dev below my average:

Last June, I did 19 dives in Jupiter, West Palm, and Boynton Beach Trip Report - Back in SE FL 2021 part 4. My RMV was 0.38 +/- 0.03 cu ft/min. Water temperature was as low as 60 degrees. Visibility was as low as 15-20 feet and there was very brisk current on several dives.

My RMV was as high as 0.44 cu ft/min, 2 std dev above my average:

So, sometimes the diving is easy, doesn't get much easier than in beautiful Bonaire

 

[scubadada]

This, nearly 5 1/2 year old thread, continues to be quite active, with 22,350 views now. There have been an additional 14 votes in the 2016 poll over the last month. Vote in the poll, if you have not done so. Change your vote in the poll if your average RMV has changed since you last voted.

The median and the mode in the 2016 poll are 0.5-0.59 cu ft/min. The weighted average is also in the mid 0.5s cu ft/min. Fifty six percent of divers in the 2016 poll have an average RMV of 0.4-0.59 cu ft/min

 

[TooCold]

Just discovered this great thread despite years of lurking on SB before joining. Will vote soon - haven't yet because I went cross-eyed looking at numbers in cu ft/min.

I found the discussion around the RMV/temperature interesting (and a little bit entertaining). Eyballing the posted scatterplots, I would be very dubious of interpreting the plotted line as a regression line. In other words, they can be fun to speculate, but a bad idea to think the data supports any prediction about RMV, given the temperature, or vice versa, or worse that it provides information to use for dive planning. This is especially true because a simple scaling of the axes will dramatically change their appearance.

I think this sums up perfectly how to approach the data:

Regardless, I have fun looking at my dive data when I am not lucky enough to be diving