SAC rate question (Um i mean another SAC rate question)

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Rileybri

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Location
Burlington, VT
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Ok down and dirty. I am a former smoker (I quit the day I found out I was going to be a father 2.5 years ago) but fairly active. A good bit of skiing in the winter and diving in the summer ect. I wish I had time to work out more or even at all but between work and being a stay at home dad I just dont have the time at the moment to go to the gym. So my question is this, I am a gas HOG (or so I am told) and having just calculated my SAC at around .85 am disgusted with my gas consumption (this was on a dive where I was doing a wet run of my new dry suit so that may have something to do with it as well.). Is it just a matter of improving my cardio efforts to get better gas times? are there specific exercises that work better then others? I want to be in the .4-.6 range? What say you wise men and women? The dive I just did that I got the .85 rat on was a fairly shallow skills based dive in 20’ max depth for 52 min. using a st72 with a starting pressure of 3k and ending pressure of 1K. like I said I was using my new dry suit for the first time as well.
 
You have to make time to exercise if you want to improve your fitness. Everyone is busy, trust me I know, but be honest with yourself - you could make the time if it were important enough to you. You don't have to go to a gym to exercise, do you? Take your kids for a jog - get a jog stroller if they are young. Too hot? Get up earlier. A friend of mine has lost a good bit of weight and improved his fitness using the P90X DVD stuff. Bottom line: you can have either results or excuses, not both.

I wouldn't use a first time in your drysuit to calculate your actual working SAC rate. How much air did you blast into it then dump out while messing about? I know for sure I did that a lot just to get a feel for that stuff. Track it, sure, but don't assume it's a true measure of what it should be once you get some more drysuit dives.

My SAC varies from .44 to over 1.0 - it all depends on what is going on during that dive. Am I just cruising along a reef with the current (eg Cozumel) or doing a salvage dive working my butt off? It's easy to to say "relax" and such, but a lot harder for some people to do it. A normal dive will be around .55 for me in single tank and a bit higher in doubles + deco bottle etc.
 
Cardio is always a plus, but physical size is a key factor too.

Why even get into an air race?
Dive a large tank, or take two!

Was it a new dry suit or your first time in one? If so, your SAC could be high just from the extra stress.


Best advice I was given in training... if you get a buddy who gets into an air comparison game, get a different buddy and a new tank!
 
Jim you are so right about results vs excuses. I mean WFC are you calling me a fat wiener ???lol Working out just was not a priority for me the past two years (working three jobs and keeping my kid alive was) until recently and although I have taken steps to drop a few lbs. I have not done much for my cardio. Oh dont get me wrong though, I dont sit on the couch and eat slim jims (any more). I am fit and I am in decent shape and stay active I just dont go to the gym to sit on an exercise bike. I do agree though I do need to get more disciplined about working on my cardio specifically.
Steve it was my first dive in my new Whites Bullet. I have probably 20 or so dives dry now so I am by no means in the muscle memory cruse along mode yet. Now that I look back I did do quite a bit of adding and dumping of air just mucking about. I guess it used far more gas then I though it would. I guess regardless of the reason why it will defiantly be a motivating factor in making improvements to my physical self! Thanks again for the replies!
 
You might notice your SAC rate drop when you stop worrying about how much gas you breath and concentrate instead on the fundamentals of diving such as maintaining neutral buoyancy, proper weighting, swim position, efficient kicking, relaxed breathing, streamlining gear, etc.

You might also find that while there are many great reasons for cardiac fitness, a lower SAC rate is not one them.
 
The dive I just did that I got the .85 rat on was a fairly shallow skills based dive in 20’ max depth for 52 min. using a st72 with a starting pressure of 3k and ending pressure of 1K.
You might want to take another look at your math.

Some common steel 72s hold about 65.5 ft3 at 3000 psi.
So at 1000 psi you will have used 2/3 of that or about 43.6 ft3.
Dividing that by 52 minutes would give you a SAC of 0.84 IF YOU HAD NEVER LEFT THE SURFACE.

But adjusting for depth would give you a lower SAC. You didn't mention average depth, but if it were (for example) 10 feet, or about 1.3 atm, your SAC would be closer to 0.65.

Obviously, I don't know the details of your cylinder, your depth profile, or your calculations, so perhaps you are correct, but it just seems pretty high for a 52 minute dive.
Is it just a matter of improving my cardio efforts to get better gas times? are there specific exercises that work better then others?
Back to your original issue, it's unclear what the relation is between fitness and SAC, but I'm in the camp that it can't hurt to be more fit. Almost all exercises are good.
The only "shortcut" of which I am aware for improving SAC is to do pretty complete exhalations, purging more CO2, and thus reducing your breathing rate.
 
I know a number of divers who are not in good cardiovascular shape...yet have low SAC/RMV rates.
Increasing one's aerobic fitness is not the only factor which might help lower the SAC/RMV rate.

The way I see it, there are several ways that a normal healthy individual can lower his/her SAC/RMV rate:
  • The wrong approach is to focus exclusively on one's breathing (rhythm, rate, depth, etc.). Others may disagree with me on this point. There's no doubt that incorrect breathing technique can increase gas consumption rates. I just think a gas hog would be better served with a different strategy. Inhale normally. Exhale fully. Breathe "normally." For some, deeper yoga-style breathing can be helpful.
  • Conduct a lot of dives -- gaining experience will lead to being more relaxed in the water. This also applies to trying out new gear, such as a drysuit. The added task-loading is sure to increase your gas consumption at first. There's also the issue of adding/subtracting gas to the suit unnecessarily.
  • Be efficient in the water -- streamline gear, weight yourself properly, optimize kicks, etc.
  • Plan the dive to involve less physical activity -- hover more to hoover less. Even dives in current can be done in an effortless manner if they are conducted as drift dives.
  • Pay attention to gear maintenance -- in particular, ensure that your regs are tuned/serviced properly.
  • Be physically fit -- with particular attention to cardiovascular fitness. As knotical pointed out, it's unclear the relationship between aerobic fitness and gas consumption rates, but there are good reasons to be fit outside of diving.

Congratulations on quitting smoking. As you know, there are many benefits to smoking cessation outside of diving.

FWIW, the secret to getting into better shape is to structure your life (work, habits, social activities, sports) so that exercise is built into it. Plan family outings to involve some sort of physical activity. Join a gym near home and/or work (convenient location is the key here). Get a work-out buddy. Ride your bike to work. Walk instead of drive. Use the stairs instead of the elevator. Join an adult sport league that has scheduled games every week. Considering the rising cost of health care and the increase of the average lifespan, staying in good physical shape is probably one of the best ways to save money in the long-run. It will almost certainly improve your quality of life as well.
 
I asked the same question a few years ago. A few things that were told to me to remember, take your physical size into consideration. I'm about 6'6 and broad build, I am naturally going to need more air than my ex who was only 5'5. Are you properly weighted/trimmed out? You may have been relaxed and comfortable, but if your doing stuff under water your going to naturally use up more air.

As far as getting better cardio - I dropped about 40lbs in the past 6 months and improve my cardio overall. All I did was stopped eating a lot of junk food. I still do, but not even close to what I used to. I have 2 dogs and when I can, bring each out separately 3x/day. That's 6 trips up and down three flights of stairs every day. I walk more to get to close places if I can (got arthritic joints and sometimes it isn't feasible. When I goto the store and joints are ok, I park further back than what I am allowed (I do have a handicap placard). When I walk I try and do so at a bit quicker pace. Given I'm not allowed to run I have to be VERY careful on the stress I put on my replacement hip.

Best of luck to you
 
Cardiovascular fitness really doesn't have a lot to do with gas consumption, unless you are doing dives that require intense effort, like spearfishing or cave diving against flow. Most diving is a lot of floating and not a whole lot of swimming . . . or it SHOULD be.

The biggest determinant of gas consumption is level of activity. Newer divers are very inefficient, using a lot of muscle activity for a very small net propulsive effect. If you are kicking or using your hands just to remain stable, you are wasting a lot of energy, and the concomitant gas! Similarly, if you have to swim all the time to keep your balance, you are also wasting energy (and most likely missing a lot of what is there to see). Spending time learning how to be motionless in the water is an excellent way to reduce your gas consumption. This may require adjusting some equipment and some weight. HERE is an excellent essay about that. And HERE is an essay I wrote about optimizing gas consumption.

BTW, a SAC rate of .8 may not be bad for a big guy. My dear dive buddy, who is one of the most relaxed and elegant divers you could ever hope to see, runs about .7. All that muscle chews up oxygen and makes CO2; it's unavoidable.
 
You might notice your SAC rate drop when you stop worrying about how much gas you breath and concentrate instead on the fundamentals of diving such as maintaining neutral buoyancy, proper weighting, swim position, efficient kicking, relaxed breathing, streamlining gear, etc.

You might also find that while there are many great reasons for cardiac fitness, a lower SAC rate is not one them.

It was a SKILLS DIVE..........I was not practicing under water basket weaving skills.
 
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