How small is your SAC?

[thanksforallthefish]

What next? See who can pee the farthest?

sounds like a good idea to me ...

While knowing SAC rate is useful and comparing it over time helps track imrpovement for newer divers, comparing it person to person is a totally useless endeavor.

couldn't agree more

After acheiving all possible efficiencies in breathing technique, SAC rates will still vary greatly person to person, based on size, weight, metabolism, dive style and regional differences in dive conditions.

again ... couldnt agree more

Who has the lowest SAC rate? Some 110 pound, even tempered, type B personality woman, who drift dives in mild current in the tropics.

... more than likely true, but I think you may be surpised

I am a 51 yo male 240lbs

Don't judge this by the tone, it's just that I don't get it. I think SAC rate is another one of those things not worth bragging about or comparing.

BTW- betcha mine's lower than yours

... totally agree

....mine for the last 200 dives

Max ... 0.6
Min .... 0.3

Avg ... 0.35

 

[drbill]

About a year or so ago I had about a 0.35. However I was in better shape then (more diving, less video editing), had a fairly warm 7mm wetsuit and my 3mm hooded vest hadn't blown off the deck of the dive boat yet. I'd hate to think of what it is now (and won't even bother calculating it based on my last few dives). However, I plan to get in better shape, buy a new 7mm wetsuit and hooded vest and return to the days when I could get three decent dives out of my HP120.

 

[J.R.]

.5 average for 'cool' waters.... occasionally get down to the .4 territory... sometimes get to the .6 territory (particularly if working with students)... but mostly aournd that .5 range...

 

[Sas]

Average over the last few months diving: 0.45. Range 0.35-0.6. Diving in water 15-17C. I am 5'10'', 75kg + female.

My SAC goes up when I do boat dives (as there is often current), when I am with new buddies, when I am trying out new gear, and when I am in my wetsuit. I think my baseline is around 0.35 as that is what I get when I am diving by myself, where I just amble around really slowly, and rarely exert myself. But I don't get those kinds of dives often! I usually do my planning based on 0.45-.5.

When I first started diving my SAC was 0.7-0.8.

 

[Teamcasa]

While knowing SAC rate is useful and comparing it over time helps track imrpovement for newer divers, comparing it person to person is a totally useless endeavor.

After acheiving all possible efficiencies in breathing technique, SAC rates will still vary greatly person to person, based on size, weight, metabolism, dive style and regional differences in dive conditions.

My thought's exactly.

My SAC rate is good for me and varies from place to place, different gear configurations, water temp, currents, whether I'm just sightseeing or videotaping. All I know is when my tank runs low, I must be finished with the dive

 

[Scuba_Jenny]

He is right, though.

Simply put, females of all species on the planet are designed by Nature for efficiency. They are the more efficient creatures in everything they do.

Males are instead designed for strength and combat. And this is inefficent, although a necessary evil, if Nature be any guide.

Yeah. Agree. Fun to brag about, but in the end it really has no bearing on whether one is a good diver or not, or their level of skill. Though when bottom time is not a factor (I do a lot of shallow diving) it is more fun for me to have somebody who can stay down as long, whether it be low SAC or big tank.

 

[Rick Inman]

I don't care what you'r sac rate is, as long as you're honest about it when we plan the dive.

Mine runs in the .5-.6 range.

 

[FlyinV]

Noob here -- I was excited my SAC rate went from 1.1 to .8 until I read this thread

At least thats what the Pro Plus 2 says it is.

but then I think I breath heavy on land so perhaps I will be cursed with a high SAC rate even when I become a better diver.

 

[TSandM]

Remember that SAC rate is related to basal metabolic rate -- The more mass you have, especially muscle, the more CO2 you make per minute, and the more air you have to move. A 6'2" body-builder is NEVER going to have the gas consumption of a 100 pound woman.

 

[bleeb]

I thought it might be interesting to throw out the following rough calculation for the sake of the discussion. This gives a vague idea of what a healthy lower limit for SAC might be.

In exercise physiology, 1 MET (Metabolic Equivalent) is defined as 1 kcal/kg/hour and is roughly equivalent to the energy cost of sitting quietly. It's also equivalent to an oxygen uptake of approximately 3.5 ml/kg/min. Converting to cfm, that's 1.24e-4 cu.ft/kg/min.

Now, assuming someone has a very efficient O2 transfer system and a high tolerance for CO2, they'd consume 4.5% of the O2 in breathing air and be exhaling 4.5% CO2. That converts to a SAC rate of 2.75e-3 cu.ft/kg/min.

For someone who weighs 180 lb (more often than not a man), this gives a theoretical lower limit for SAC of 0.225 cu.ft/min. OTOH, the previously mentioned 100 lb woman could have a SAC of 0.125 cu.ft/min.

The error bars are fairly large and that there are lots of hidden assumptions. Some major ones would include: What's the definition of 'resting' and how close to that can someone get while diving. 'Sleeping' is even lower energy state than 'resting' although the line is probably fairly fuzzy and if person were capable of getting their body to operate at the lower level, that would improve their energy consumption. Temperature and cardiovascular conditioning have also already been mentioned. Some of the body's energy processes are anaerobic, and I don't know if the replenishment timescales are long enough that you wouldn't be burning oxygen to re-stock them until you're back on the surface. Body composition is also a factor, since anything that averages muscle, fat and bone must be an approximation.