Average Gas Consumption

[scubadada]

Are you really expecting this poll to show a "normal" distribution?

I see a few problems.

1. ScubaBoard participants in general are nowhere near normal. A similar poll a few years ago indicted that a slight majority of divers (at least on ScubaBoard) use back plates and wings; in the real world, BP/Ws amount to about 1% of BCD sales annually.

2. You are asking people to self report a figure they are likely to want to boast about or not report if they are not feeling boastful.

3. Self reporting surveys regularly are oversampling people with a motivation to report.

4. How accurate are the reports of these people? A year or so ago, I had a new tech student tell me he already knew his RMV because he had an air integrated computer that gave it to him. Now, that was all recreational diving, but it was impressive--much better than mine has ever been. I am sure he was telling the truth, but our work in class showed he was nowhere near that. We have done a number of dives together since then, and he has never done as well as I.

Sampling bias - Wikipedia, the free encyclopedia

Yes, the poll has many shortcomings, you've mentioned a few. However, there's little information available for a topic with a lot of discussion. If enough participate, the general results will be of interest, even in light of the clear limitations.

 

[Aquavelvet]

My typical of 0.5 cu ft/min is for cold water, deeper dives, and all the gear that entails. It does drop a bit lower in warm water, but it takes me a couple days to adjust and relax in the nicer conditions.

 

[admikar]

First year- best ,6; worst ,97; avg. ,73. Worst was OW1 dive.
This year- best ,49; worst ,96; avg. ,7. Worst while towing a surface marker, that got tangled, on nav exercise. Best on a night dive. All dives in dry suit.
If drop all training dives avg ,59.

 

[scubadada]

I didn't start calcutating my RMV until about 450 dives, when I bought my Oceanic VT3. My RMV has changed very little over the 750 dives since then and I do not expect it to. It probably also largely explains my relatively narrow range of RMVs

 

[boulderjohn]

I didn't start calcutating my RMV until about 450 dives,

I think the same is true for a lot of divers. The overwhelming majority of divers will never see that number of dives. In fqact, I beleive the overwhelming number of divers will never know the meaning of SAC/RMV. Are those people included in the range we call "norma/"? Is it possible that in order to tell someone your RMV, you have to be well above the median already?

 

[gopbroek]

Warm water drift diving in the Caribe around .38/9. Same area but add a spear and it goes up 10% to around .43 due to increased activity. Throw in a heavy current and bouncing to 150' while hunting on the wall in Cozumel up to .47/9. These #'s might sound good compared to folks up north but I think that if I was in a dry suit or even in a 7MM fighting hypothermia my rate would be substantially higher. To compare rates between substantially different types of diving is like comparing apples to oranges.

 

[boulderjohn]

Warm water drift diving in the Caribe around .38/9. Same area but add a spear and it goes up 10% to around .43 due to increased activity. Throw in a heavy current and bouncing to 150' while hunting on the wall in Cozumel up to .47/9. These #'s might sound good compared to folks up north but I think that if I was in a dry suit or even in a 7MM fighting hypothermia my rate would be substantially higher. To compare rates between substantially different types of diving is like comparing apples to oranges.

This is in part due to difference in definitions of SAC/RMV. Different people and different agencies use the terms differently, and each insists everyone else is using the terms incorrectly.

In the case of one agency in which I was trained, they would say that your examples are using the term incorrectly. They would say you have only one RMV, and you then make adjustments for all those differences with you plan the dive. You already know you have to multiply by your ATA to calculate gas consumption; that agency said you have to also multiply by a number you arbitrarily assign to the dive difficulty as well. Personally, I find that silly--how in the world is that number I produce going to be at all accurate?

 

[scubadada]

Warm water drift diving in the Caribe around .38/9. Same area but add a spear and it goes up 10% to around .43 due to increased activity. Throw in a heavy current and bouncing to 150' while hunting on the wall in Cozumel up to .47/9. These #'s might sound good compared to folks up north but I think that if I was in a dry suit or even in a 7MM fighting hypothermia my rate would be substantially higher. To compare rates between substantially different types of diving is like comparing apples to oranges.

I'm sure this is the case. Included in my average RMV are 3, 5, 7 mm wetsuits, 47-85 degrees, no current to ripping current, wrecks, reefs, 15-160 foot depths, minor equipment problems...

 

[scubadada]

This is in part due to difference in definitions of SAC/RMV. Different people and different agencies use the terms differently, and each insists everyone else is using the terms incorrectly.

In the case of one agency in which I was trained, they would say that your examples are using the term incorrectly. They would say you have only one RMV, and you then make adjustments for all those differences with you plan the dive. You already know you have to multiply by your ATA to calculate gas consumption; that agency said you have to also multiply by a number you arbitrarily assign to the dive difficulty as well. Personally, I find that silly--how in the world is that number I produce going to be at all accurate?

I would rather know my own average RMV, that takes into account the dive variables, than use a single value and adjusting it, somewhat arbitrarily, based on expected dive characteristics

 

[Kevrumbo]

This is in part due to difference in definitions of SAC/RMV. Different people and different agencies use the terms differently, and each insists everyone else is using the terms incorrectly.

In the case of one agency in which I was trained, they would say that your examples are using the term incorrectly. They would say you have only one RMV, and you then make adjustments for all those differences with you plan the dive. You already know you have to multiply by your ATA to calculate gas consumption; that agency said you have to also multiply by a number you arbitrarily assign to the dive difficulty as well. Personally, I find that silly--how in the world is that number I produce going to be at all accurate?

I would rather know my own average RMV, that takes into account the dive variables, than use a single value and adjusting it, somewhat arbitrarily, based on expected dive characteristics

btw, Your SPG reads in pressure units --not volumetric units: Why don't you derive & utilize a pressure SAC Rate from your RMV for the actual cylinder you're using?? You pre-dive gas plan with RMV to select the proper cylinder(s) for the total gas volume needed, but you should track & monitor gas consumption on the actual dive with a pressure SAC Rate per ATA.

If during the dive, the realtime on-the-fly expected SPG or AI reading is 30% or more consumption than you figured of your nominal pressure SAC Rate at that depth, then that indicates you are physically working and/or breathing harder than normal, or have a leak somewhere in your reg/gear set-up, and should consider aborting the dive. (And this your "arbitrarily assigned dive difficulty number" example and how to use it).