2nd Percentile SAC Rate

[joebob24]

I have had pretty consistent SAC rate of 1.2 cu ft/min over my first 25 dives or so. Occasionally it is as high as 1.6 if I am crabbing. I am relatively active and 6'1", 230lb. According to the thread on Average Gas Consumption, only 2% of people have a SAC rate above 1. Are there any medical conditions that could cause this? I checked my weighting and trim, tried jogging for a few months and tried to just relax under water and nothing seems to really change it much. Starting to wonder if my lungs just don't work like they should.

 

[Brett Hatch]

When you look at that poll, keep in mind the selection bias for experienced divers here, and the way that people often over-estimate their own abilities. If you are in the worst 2% in that poll, I very much doubt that extrapolates out to the worst 2% of divers overall.

Most new divers can dramatically improve their air consumption by slowing down, like way down. Try to minimize your extraneous movements. To facilitate this, see if you can get a friend to film you for a few minutes some time -- you might be surprised by how much fiddling you do, I know I was. If you're going through your gas much more quickly than the people around you, maybe a bigger tank will be helpful. But as you get better at diving and gain more experience, it will come down some.

Cheers

 

[RyanT]

Starting to wonder if my lungs just don't work like they should.

Doubtful, for starters, you are likely flailing around too much. Muscles burn oxygen. The more you use them, the more you burn. Are you swimming a lot? Slow down. Do you scull with your hands? If so, stop. Work on your trim so that you aren't sculling with hands and feet to hover and turn. Move slow. This is where you want to start.

 

[boulderjohn]

It has been a long time since I looked at that thread, but IIRC correctly, I participated by strongly cautioning against drawing any conclusions from it. It is bound to present an unrealistic range of results.

• It is on ScubaBoard, a forum highly overrepresented by experienced divers. Another SB forum found that the majority of participants use a BP/W setup for their BCD, and about the time of that survey, an industry survey of the scuba retailers showed that BP/Ws represented 1% of BCD sales. In my area, the vast majority of dive shops do not stock BP/Ws.
• The survey called for voluntary participation. I don't recall if I participated, but I hope I didn't, for the very reason exemplified by the opening post. When people voluntarily participate in a survey, the ones who participate tend to be at the extremes, and if one extreme is clearly bad, then that extreme gets little partitication.
• As results get published while people are still participating, later participants tend to skew their responses in the direction of the majority.

So I do not believe that any survey of ScubaBoard participants on any topic will come anywhere close to reflecting the range of behaviors in the diving public.

 

[Superlyte27]

I have had pretty consistent SAC rate of 1.2 cu ft/min over my first 25 dives or so. Occasionally it is as high as 1.6 if I am crabbing. I am relatively active and 6'1", 230lb. According to the thread on Average Gas Consumption, only 2% of people have a SAC rate above 1. Are there any medical conditions that could cause this? I checked my weighting and trim, tried jogging for a few months and tried to just relax under water and nothing seems to really change it much. Starting to wonder if my lungs just don't work like they should.

You’re doing fine. You just need more dives. It’ll fix itself.

 

[scubadada]

Yes, your RMV is on the high side Average Gas Consumption
You are diving in challenging conditions with a wetsuit or a drysuitl Just keep diving and see what happens to your RMV. I would not be surprised if it improved. Dive with an appropriately sized cylinder for your dives.

 

[joebob24]

All good info so far. Strangely enough, I hadn't thought much about the bias for experienced divers on SB. I could see that bias combined with the negativity associated with having a high SAC rate have a pretty big effect on the results.

As far as tank size, I already dive cave filled LP108 doubles most of the time, so I don't think bigger is really an option. I actually just switched to HP100 doubles because even for me that was just more air than I could use on a rec dive. They are also so big that I am sure they don't help the SAC rate at all.

 

[FF / EMT]

It has been a long time since I looked at that thread, but IIRC correctly, I participated by strongly cautioning against drawing any conclusions from it. It is bound to present an unrealistic range of results.

• It is on ScubaBoard, a forum highly overrepresented by experienced divers. Another SB forum found that the majority of participants use a BP/W setup for their BCD, and about the time of that survey, an industry survey of the scuba retailers showed that BP/Ws represented 1% of BCD sales. In my area, the vast majority of dive shops do not stock BP/Ws.
• The survey called for voluntary participation. I don't recall if I participated, but I hope I didn't, for the very reason exemplified by the opening post. When people voluntarily participate in a survey, the ones who participate tend to be at the extremes, and if one extreme is clearly bad, then that extreme gets little partitication.
• As results get published while people are still participating, later participants tend to skew their responses in the direction of the majority.

So I do not believe that any survey of ScubaBoard participants on any topic will come anywhere close to reflecting the range of behaviors in the diving public.

This is pretty spot on.

 

[johndiver999]

If you are diving double steel tanks on recreational dives, then why the heck do you care about your sac?

Seriously, if you are not going to get two dives out of the tanks, just do your dives, don't run out of air (which should be hard to do if you are diving over 50 feet) and have fun. People make a low sac into some sort of game or competition (which makes little sense to me). Eventually your sac should come down unless you are very active.

 

[scubadada]

All good info so far. Strangely enough, I hadn't thought much about the bias for experienced divers on SB. I could see that bias combined with the negativity associated with having a high SAC rate have a pretty big effect on the results.

As far as tank size, I already dive cave filled LP108 doubles most of the time, so I don't think bigger is really an option. I actually just switched to HP100 doubles because even for me that was just more air than I could use on a rec dive. They are also so big that I am sure they don't help the SAC rate at all.

Wow, that is a lot of gas!