SAC rate?

[Linedog]

OK so I have this AI dive computer that tells me all kinds of stuff. I tell it what size tank I dive with and it tells me my SAC rate. That's nice and all, but whats a good rate?

[renoun]

I assume you are familiar with Bob's Gas Management Article or Lamont 's Rock Bottom and Gas Management for Recreational Divers but if not I would suggest reviewing them.

The short answer is .6-.75cfm SAC is probably pretty typical for a unstressed diver. A very relaxed small person might get down to .35-.40cfm SAC. Lots of factors matter so your mileage may vary.

[Grateful Diver]

OK so I have this AI dive computer that tells me all kinds of stuff. I tell it what size tank I dive with and it tells me my SAC rate. That's nice and all, but whats a good rate?

A good rate is highly dependent on the diver and the conditions of the dive. For some, anything above about .5 CF/min sucks ... others do a happy dance if they get below twice that rate.

What you should do is record what your computer is telling you on each dive ... and think about what causes it to go up or down from dive to dive.

For most of us, our SAC rate was very high when we started diving ... and declined over time as we got better skills and more relaxed in the water. Conditions such as current, cold, or anything that causes stress will tend to make your SAC rate increase ...

... Bob (Grateful Diver)

[Jeff Pack]

I started at 1.04. I'm now down into occasional 70's, and solidly in the 80's.

As Bob noted, stress, cold current, even depth affect your SAC

[Peter Guy]

Question: "What is a good SAC rate?"

Answer: "One that lets you do the dive you want with the amount of gas you have."

That is really like asking "What is a good MPG?" And the answer, which is really the answer to almost all Scuba questions, is "It depends."

The real value of knowing a SAC Rate trend (one can never know what one's SAC rate will be for a particular dive) is to allow you to plan your dive based on your trend for that type of dive. Once you get into the water, you'll then DO your dive based on what is actually happening, as opposed to what you had hoped (i.e., planned) to happen. And then next time you'll have more information on which to base your planning.

[LCF]

A "good" SAC rate is one that reflects steady, rhythmic, relaxed breathing, that doesn't waste gas and doesn't result in a CO2 headache from trying to reduce one's SAC rate

What that value will be will depend on a lot of things, including your diving style (do you swim a lot, or mosey, or hover), your age, size and fitness level, how comfortable you are in the water, and how efficient you are. But it isn't very predictable -- I've done cave dives with a 6 foot, fairly fit man, where we swam all the time, and his SAC rate had to be .3 or below. One of my favorite buddies is a 6 foot, fairly fit man, and his SAC runs about .7.

Don't obsess about the number -- just use it to make sure you have the gas you need for the dive you intend to do.

[Paulicarp]

Don't obsess about the number -- just use it to make sure you have the gas you need for the dive you intend to do.

+1 on that point. just like MPG in your car, less is always better, but unlike gasoline consumption, using more doesn't cost you more. Use what you need for getting the CO2 out of your system, but most importantly, get familiar with how much you're using. If you track it frequently, you can get a good feel for how much you're using at any given point in the dive. This is really helpful for decision making on the fly when things don't go as planned. If you have to fight some current you didn't expect, you have a better idea when to make that decision to turn and still have plenty of reserve gas left when you exit.

[Linedog]

OK, I don't obsess about it I was just wondering mostly because it is what it is. I skimmed over the suggested reading and plan to sit down and read it carefully later, thanks for the link. I'm very comfortable in the water, I like to mosey, but need work on my trim so I struggle with the last 1500 psi as it seems my tank (HP 130) wants to go ass up. But I guess I kinda look at it now as my dive mpg. Good SAC is was a nice relaxing dive, high SAC I musta been fighting something, trim current etc.

[Paulicarp]

OK, I don't obsess about it I was just wondering mostly because it is what it is. I skimmed over the suggested reading and plan to sit down and read it carefully later, thanks for the link. I'm very comfortable in the water, I like to mosey, but need work on my trim so I struggle with the last 1500 psi as it seems my tank (HP 130) wants to go ass up. But I guess I kinda look at it now as my dive mpg. Good SAC is was a nice relaxing dive, high SAC I musta been fighting something, trim current etc.

Just to be clear, I wasn't (and I don't think Lynn was) saying that you are obsessing, just that *what* your SAC or RMV is is less important than you knowing in general what your range of consumption normally is like. Some of the factors are not things you can change, some are things you can change. So SAC or RMV is helpful to find ways you can improve, but it's most helpful to know what your consumption is so you can plan well and make informed decisions as you dive.

Also, keep an eye open for the free gas management semiars that guys like Bob, Brian and Scott occasionally teach; they are very highly recommended.

[Linedog]

No I didn't think anyone thought I was obsessing on it. It's all good. My last 2 dives I had a .62 and a .66 so I was just wondering what an average was. I'm still a new diver (less than 1000 dives) and I'm still in my learning curve.

[Joshua Smith]

No I didn't think anyone thought I was obsessing on it. It's all good. My last 2 dives I had a .62 and a .66 so I was just wondering what an average was. I'm still a new diver (less than 1000 dives) and I'm still in my learning curve.

ROFL! "less than 1000 dives?" I like that. I'm probably less than halfway to 1000, myself. One of my early mentors told me that he tried to learn something on every dive. I liked that also.
Fwiw, I'm a fairly consistent .7 SAC. Sometimes a little better, sometimes worse.

[dwashbur]

Good answers so far. My first thought was "Asking what's a good SAC rate is a bit like asking, how long is a piece of string?". But that makes me sound like a much bigger a**hole than I actually am. I average about .65, and if it goes over .7 I know there was something off about the dive. It might be current, temporarily losing a buddy, getting excited about the biggest or smallest octopus I've ever seen - most recently it had to do with buddies who were having major gear problems. I generally consider my SAC rate acceptable if I a) come back alive, b) have at least 500 psi left in the tank when I break the surface, and c) know all my buddies are safe.

I've been able to lower my SAC rate by forcing myself to breathe to an internal count. If there are no stressors and I'm just enjoying the critters and the peace, I go with a slow 8 count. If it feels like I'm breathing too fast, I'll extend the exhalation to a 12 count. If stuff starts happening and I can't maintain it, I try to at least keep up a 4 count. Sometimes it works, sometimes it doesn't, but I've found that having some kind of inner cadence to my breathing helps me keep it under better control. That might work for you or it might not, and that's okay. A friend of mine doesn't count, but he tries to make sure he takes twice as long to exhale as he does to inhale. There are a gazillion techniques out there, so I'd suggest you experiment and figure out one that works best for you.

[lavachickie]

Lots of good points. Comparing to others is really hard; it's very helpful as a way to guage your own performance over time. You'll see it drop in your first few months of diving (assuming you are diving routinely) as you become more skilled and relaxed.

In good conditions with no stress, I am around .48. I am NOT a "small person." I'm probably one of the biggest women diving around here. So generalities are just that.

It's also fun to see just how great an improvement you'll see if you add some cardo workout to your life if you don't already do so. Even something simple like the C25K program (interval walk/run training).

[kdupreez]

A general rule of thumb is between 6.0 an 7.5 is not bad.. and "controlled" stressed (not panicked) conditions around 1.0

to make things easy, for typical dive planning, we just use a standard of 0.75 for everyone on the team..

BUT - you should at lest know what your RMV/SAC/SCR rate is for both non stressed an stressed conditions..

.

[LCF]

I think .7 is bandied about as an average for an adult male, with women generally being lower. New divers can easily be over 1.0. Experienced cave divers have amazingly low SAC rates, but absolute efficiency is the hallmark of good cave diving.

Fwiw, I'm a fairly consistent .7 SAC. Sometimes a little better, sometimes worse.

Just out of curiosity, how does a rebreather diver have any idea what his SAC rate is?

[dwashbur]

In good conditions with no stress, I am around .48.

You've certainly given me a target to shoot for! I've gotten down to about .56 but that's the best so far.

[LCF]

I run in the low .3s, and the 6 foot man I cave dove consistently uses less gas than I do. Irks me no end!

[BASSMAN]

I run in the low .3s

Not an original thought but, some day, I wish someone would accuse me of, "Breathing like a girl", then I know I have a good SAC rate. I'm usually between a .60 or.50 after 600+ dives. My rate seems to be better on night dives.

[Jeff Pack]

Lots of good points. Comparing to others is really hard; it's very helpful as a way to guage your own performance over time. You'll see it drop in your first few months of diving (assuming you are diving routinely) as you become more skilled and relaxed.

In good conditions with no stress, I am around .48. I am NOT a "small person." I'm probably one of the biggest women diving around here. So generalities are just that.

It's also fun to see just how great an improvement you'll see if you add some cardo workout to your life if you don't already do so. Even something simple like the C25K program (interval walk/run training).

I do chair Pilates as well as Cardio on an elliptical. Almost seems to me to be a disadvantage, because from my mountain climbing days, we're taught to breath really deep and cardio enforces that.

Maybe if i get a can light, it'll improve my SAC...

[Scrappy]

When I started out (first 30 dives) I was well above 1. Now I range from.6-.8. Depending on the dive. I was told this was normal. Now I focus on breathing using a count method , or just by taking a quick break underwater to meditate for a minute to get into a rhythm .

[Tom Nic]

I run in the low .3s

Not an original thought but, some day, I wish someone would accuse me of, "Breathing like a girl", then I know I have a good SAC rate. I'm usually between a .60 or.50 after 600+ dives. My rate seems to be better on night dives.

Plus 1 on wishing I could breathe like a girl.

I am an old fat guy on my way to being an old healthy guy but have nonetheless consistently been in the .5's for a number of years now. Wish it was better, but it probably is what it will be. (Talk to me in a hundred pounds or so).

It is kind of fun 'outbreathing' your skinnier, 10 yr younger dive buddies, though! .

In Bonaire my sac rate drops at least a full point. Kinda nice since you are somewhat stuck with Al 80's.

Keith, I know you LOVE night dives, and I think I understand the increased relaxation that leads to a lower sac. When the darkness is kind of like a cocoon, and your vision shrinks just to the area of your light, one enters a relaxed, almost meditative place that is tons of fun.

[whatevah]

Good discussion It has taken me a lot of dives to bring my SAC down from 0.7 - 0.8 to the present 0.2 to 0.3. I think that most of the improvement just happens with experience, but there are some things that I think have kept me progressing - maybe they'll work for others too:

* got rid of excess lead from my belt and minimized/simplified my equipment configuration (switching from an old-skool jacket style BCD to a backplate/wing was key to improved trim and reduced drag)

* got rid of the ankle weights I was told were necessary for diving in my drysuit - there are better ways to adjust trim

* improved aerobic fitness and dropped from 190+ lbs to 170 lbs

* exposure to adverse conditions and task loading has taught me to control my breathing and stay calm (thank you Skagit Dive Rescue!)

* learned to work with the current rather than fight it - much better to plan dives to take advantage of the flow, and to eddy out from time to time

Recently I have become a firefighter - figured that my SCUBA breathing control would just transfer right over to SCBA. Wow, was I wrong. I might have a little flatter learning curve than some, but with new equipment and all kinds of new stresses I am having to learn all over again!

[lamont]

I don't think any one has mentioned it yet, but if you're over-using your lungs for buoyancy control that can burn through quite a bit of gas and can also lead to some CO2 buildup if you're deeper.

If you're not breathing relaxed and you're breathing off the top of your lungs than you're either holding your breath (building up CO2 here), or else you'll tend to exhale quickly and inhale quickly and then pause at the top of your lungs, and that burns gas.

Becomes much more obvious in cave on the ups and downs, or running the reel, but the same principle applies to open water as well. Its better to get properly neutral, breathe with a normal rhythm and not be using the top or bottom of your lungs.

(and i mention that because i was paying attention to that today -- dove Xunaan Ha today and i got to be #2 and chill and watch my technique closely which was nice -- and i barely used any gas on the dive)

[pogiguy05]

If you cannot lower your SAC just buy a bigger tank I dive 130's have a sac rate of around .5-.6 and get a good hour dive and end with about 800-1000psi. If I truly wanted to go longer than 1 hour I think I would just go for the rebreathers. If you feel up to it double up a pair of 130's and show how macho you can be.

[BASSMAN]

If you cannot lower your SAC just buy a bigger tank I dive 130's have a sac rate of around .5-.6 and get a good hour dive and end with about 800-1000psi. If I truly wanted to go longer than 1 hour I think I would just go for the rebreathers. If you feel up to it double up a pair of 130's and show how macho you can be.

You Suck like a Kirby Vaccum cleaner!