Average Gas Consumption

[scubadada]

76 responses to date, pretty normal looking curve with a tail on the higher end. Clearly, most who reported have RMVs 0.4-0.59.

 

[kensuf]

I think people tend to underestimate their real SAC rate. Every six months, or so, I do a test to validate the numbers I use for dive planning are still good. The test is simple, run a line course at a fixed depth, check starting pressure, swim back and forth for 10 minutes, check ending pressure. Do the math on the surface and now you know.

 

[scubadada]

I think people tend to underestimate their real SAC rate. Every six months, or so, I do a test to validate the numbers I use for dive planning are still good. The test is simple, run a line course at a fixed depth, check starting pressure, swim back and forth for 10 minutes, check ending pressure. Do the math on the surface and now you know.

I agree with you, many divers probably don't have a very good idea of their average RMV, even if they occasionally do the calculation (assuming they have a reasonably accurate measurement of their gas use and average depth). I've been diving an air integrated Oceanic VT3 for the last 6 years/750 dives, and have my RMV for all of those dives. My average RMV, and its variability, reflects all of the various conditions I have dived in that period. I did not start checking my RMV like this until I had about 450 dives. My average RMV has not changed much over the six years and I don't expect it will.

An AI computer and download software makes it particularly easy to follow your RMV. As an example, this is my last dive, OceanLog software:

In addition to the above, the profile also gives you ascent rate violations, if any, and deco information.

 

[wspalding]

76 responses to date, pretty normal looking curve with a tail on the higher end. Clearly, most who reported have RMVs 0.4-0.59.

View attachment 377486

That is NOT a very normal bell curve, it has a very definite skew (from a statistician's perspective).

 

[boulderjohn]

That is NOT a very normal bell curve, it has a very definite skew (from a statistician's perspective).

As a said earlier, this is not a normal distribution, and I am not sure what we have learned from this.

If, as has been suggested, the average diver does not know his other RMV until having completed hundereds of dives, then the average diver will never know that RMV. The means the average diver is not even represented in this distribution.

ScubaBoard has an unusual client population. As reported earlier in this thread, past surveys on BCD preference indicate that more than half of ScubaBoard users, at least half the ones participating in the survey, use a back plate and wing. In contrast, national retail data indicates that back plates and wings make up about 1% of total sales in the U.S.

Self reporting data is always subject to other forms of selection bias as well.

Self reporting data is always subject to the accuracy of the reporting, especially when the terms are not defined and everyone is free to use his or her own definition.

So I am not at all sure what has been accomplished here.

 

[Sleepdr]

I'm not a highly experienced diver, and freely admit to hoovering air at this point.

In Maui doing a shallow, relaxing dive with a 2-3mm suit: I was around 0.4scfm

Yesterday, 55 degree water, vis 6' at best, 14mm neoprene, and cruising around 66' for most of the dive: 0.7-0.8scfm.

I really need to get the LP98s back in hydro and take a drysuit class for my trilam suit sitting in the storage room. That 7mm Goldcore wetsuit is too small and a recipe for overheating on the surface.

 

[scubadada]

OK, no new votes on the poll for several days, this thread appears to be done. 94 votes in the poll:

There was a very similar poll in 2009 and the distribution curve looks very similar though there was 149 responses:

I took a few minor liberties in formatting the two polls to be displayed identically. Though probably statistically illegal, the combined poll with 243 responses:

Posters often ask what is an average RMV? As pointed out by several, the SB polls are biased by participants on SB, divers savvy enough to know about and calculate their RMV, reporting bias in the RMV submitted... Regardless, I think this information is quite consistent and interesting. 55% of divers reporting have a RMV between 0.4 and 0.59 cu ft/min. The median and the mode are contained within this range. The bottom 10%ile is somewhere in the 0.3s and below. The top 10%ile is around 0.7 and above. Regardless, this is better data than one's personal opinion. There you go.

 

[Bob DBF]

Posters often ask what is an average RMV? As pointed out by several, the SB polls are biased by participants on SB, divers savvy enough to know about and calculate their RMV, reporting bias in the RMV submitted... Regardless, I think this information is quite consistent and interesting. 55% of divers reporting have a RMV between 0.4 and 0.59 cu ft/min. The median and the mode are contained within this range. The bottom 10%ile is somewhere in the 0.3s and below. The top 10%ile is around 0.7 and above. Regardless, this is better data than one's personal opinion. There you go.

What is interesting to me is that I am at the high end, around 0.7, and when diving with other divers I manage to bring back more air to the boat than they do. So I do believe this poll is skewed to the very serious diver rather than the average diver.

Normally I dive cold, low viz water, both salt and fresh, in a 7mm farmer john and cover ground hunting for food or lost treasures on the bottom. I've only calculated air consumption since I bought a computer 400ish dives ago, and have had a low of 0.5 and a high of nearly 2 when salvaging some anchors and filling lift bags. I have never tried to conserve air, except in an emergency, and if I need more air when planning a dive I find a larger tank or more of them.


Bob

 

[scubadada]

Hi Bob,

Absolutely, the SB polls do not reflect average divers. I would imagine the "average" diver does not know what an RMV is and probably does not actively participate in SB. You're certainly not an average diver either

Good diving, Craig

 

[gcarter]

What is interesting to me is that I am at the high end, around 0.7, and when diving with other divers I manage to bring back more air to the boat than they do. So I do believe this poll is skewed to the very serious diver rather than the average diver.

Normally I dive cold, low viz water, both salt and fresh, in a 7mm farmer john and cover ground hunting for food or lost treasures on the bottom. I've only calculated air consumption since I bought a computer 400ish dives ago, and have had a low of 0.5 and a high of nearly 2 when salvaging some anchors and filling lift bags. I have never tried to conserve air, except in an emergency, and if I need more air when planning a dive I find a larger tank or more of them.


Bob

In another thread, someone posted that 0.7 was chronic hyperventilation. Apparently you and I hyperventilate on all of our dives.