Trying to transition from total-noob, part 2

[egs]

Hi, me again.

So I've only got 19 dives in since OW, but I'd still like my gas consumption rate to go down. My computer usually shows my SAC at a bit above 1, and I can consider it a triumph if I can get it to something like .95, but I talk to divers whose gas lasts a *lot* longer than mine. I've read posts from people saying their SAC was about .6, maybe .5, and I even thought I met a diver who swore she ended a dive with more gas in her cylinder than she started with.

I feel pretty relaxed on my dives, but clearly move a bit more than I should. Even so, I'm surprised that my 100 cu ft tank only gets me about 40 minutes of bottom time if my average depth is about 40 feet.

So since I'm shamelessly soliciting wisdom from the group, I'll hope you don't mind if I ask what I should be doing, other than more dives, to work on decreassing my gas consumption rate.

Apologies if the posts aren't totally appropriate for the group, but every time I log in, scubaboard politely nags me for not posting more and thus far this is all I've got.

Cheers,

-- Eric

 

[Gombessa]

So since I'm shamelessly soliciting wisdom from the group, I'll hope you don't mind if I ask what I should be doing, other than more dives, to work on decreassing my gas consumption rate.

Hi Eric,

The two things that seemed to help the most for me are:

1) Dive more--the more (and more frequently) you dive, the more comfortable you become in the water, the lower your anxiety level, and lower your breathing rate becomes. Even if you feel pretty comfortable now, you're probably not as relaxed as you would be lounging on a lawn chair, right?

2) Achieve neutral buoyancy--your body uses a lot of oxygen when you move around, swimming up or down, sculling with hands to turn around or arrest your motion, etc. Diving should be an exercise in floating, and if you can "float" in the water motionlessly, you're spending a lot less energy just trying to stay still, and that will be reflected in your gas consumption.

Either way, make sure you continue to have fun; I bet every diver here has gone through the "my gas consumption rate is atrocious!" phase, and it too, shall pass.

 

[deep-descent]

Eric,
Dive Dive Dive.... Its the best way to improve, but cardiovascular fitness will help along with streamlining your gear and position in the water. Get horizontal and practice your frog-kick, push less water.

To add to Gombessa, fine tune your buoyancy, allot of new divers waist allot of air on that power inflater. Practice get it dialed in and just relax. it will come, good luck !!!

 

[egs]

Thanks - this is kind of what I expect. I imagine that there are other factors at work, too. All other things being equal, I'd imagine a large person to consume gas at a higher rate than a small person, and so comparing SACs isn't a very exact science.

And I'd expect that a very fit person would consume gas more slowly than a less-physically-fit person.

I can work on more dives, of course, and I can work on moving less. When I think about it on a dive I am aware that even when not doing anything my arms and legs are moving more than they should as I try to maintain position.

I'm looking forward to looking back on this with a sense that I was once such a noob.

 

[nkped]

Keep at it. I can tell you from experience that it may take a while but it's worth it.

 

[Gombessa]

Thanks - this is kind of what I expect. I imagine that there are other factors at work, too. All other things being equal, I'd imagine a large person to consume gas at a higher rate than a small person, and so comparing SACs isn't a very exact science.

And I'd expect that a very fit person would consume gas more slowly than a less-physically-fit person.

All of these make a difference, but wherever you stand, your SAC rate at 19 dives is quite different than what it will be at 59 or 119 dives.

1.0 is pretty high, though not uncommon for new divers; it's what a lot of people use as calculation for a diver under stress. No matter how big you are, you can likely get it down to the range of 0.6--0.7 (you probably won't hit 0.3-0.4, which some small females I know do on a regular basis).

Hopefully that gives you some hope! It's never a lost cause, and there is no magic pill that you're missing out on

 

[paddler3d]

You're SAC rate will improve with experience. You may just be one of those with a high metabolism.

A couple I dive with we all have different SAC rates. Mine is around .7cfm. On the exact same dive, I use a HP130, Matt uses a HP100 and Steph uses and AL80. I like to hold a bit more in reserve, but I'll end up with 1k and they'll both have 500psi left.

I gave up after a while and just accepted it.

 

[TSandM]

Here is an essay I wrote on this some time back:

How fast you use your gas is determined by two things: How much CO2 you are generating per minute, and how efficiently you use the gas you breathe to accomplish gas exchange in the lungs.

To address the second idea first, I'm going to describe a little anatomy. Your respiratory system includes your mouth, larynx, trachea, large bronchi, small bronchioles and then the air sacs where gas exchange actually takes place. Until gas gets into the air sacs, it's just passing through -- it's not delivering any oxygen, or taking away any CO2. If the volume of air you breathe with each breathe is only the volume of your larynx, trachea and bronchi, you're moving a lot of air, but not exchanging any gas. That's why shallow, rapid breathing runs through your tank quickly (and also leaves you feeling short of breath). It's also why slow, deep breaths are routinely recommended by instructors.

Tension and anxiety tend to make people take quick, shallow breaths, which are inefficient. Relaxation tends to allow people to slow their breathing . . . but the funny thing is that slowing your breathing also tends to bring relaxation with it. That's the essence of yoga breathing, or meditation.

Assuming your breathing PATTERN is an efficient one, then you have to look at your CO2 production, which is a result of metabolic activity in cells. You have a certain basal metabolic rate, below which you really can't go. It's actually HIGHER in fitter people than it is in the unfit, so you'd think that getting fit would make your gas consumption worse. But at the same time that your basal metabolic rate increases, the amount of muscle effort you need to accomplish a given amount of work goes DOWN, and that's a much bigger influence. So fitness does pay off.

But efficiency pays off even better. Every motion you make underwater, you pay for with some gas used. Therefore, the less motion, the longer your gas lasts. You can reduce motion by becoming horizontal, so that all your kicking effort succeeds in propelling you forward. If you are tilted at a 45 degree angle to the bottom, each time you kick, you drive yourself upward. To compensate, you have to keep your buoyancy negative, so you will have an equal tendency to sink. At that point, you are expending energy for a net displacement of zero! Very inefficient, and a very common new diver error.

Use your fins, not your hands. Hands are great for swimming on the surface, without fins, because your feet aren't very efficient propellers. But fins are, and that's what you should be using underwater. Flailing wildly with the hands uses a lot of muscle effort and produces very little net propulsion, so people who swim with their hands tend to suck gas.

Master your buoyancy. Although the volume of gas going into your BC or drysuit is relatively small, if you are putting it in and letting it out and putting it back in and letting it back out . . . after a half hour, your BC has breathed a lot of your gas. To master buoyancy, you have to start with proper weighting, because being significantly overweighted will make you unstable in the water column, and result in a lot of yo-yoing that wastes BC gas and ALSO makes you breathe harder. So reducing your weight to the proper amount will, in the long run, make your gas last longer.

And finally, move slower! One of the major strategies of sea life is camouflage, so if you move quickly, you miss many animals you might otherwise find. Unless you have a specific purpose for rapid movement, like spearfishing (and spearfishermen are NEVER going to win any awards for low SAC rates!) slow swimming will result in a much more productive and interesting dive.

Finally, recognize that body size and muscle mass will have a detectable effect on gas consumption. My favorite dive buddy is 6' tall and very strong. He's an absolutely beautiful diver -- quiet, relaxed, balanced and efficient in the water -- but he will never equal my SAC rate, because I'm a little old lady. If you habitually dive with people who are much smaller than you are, then buying bigger tanks may be your best answer.

Hope some of that is helpful.

 

[dannobee]

My lowest SAC rate was 0.33, and I'm a fat old man. It's usually around 0.45-0.5 in the temperate waters of Monterey and Carmel. It was similar in Alaska, but it's always lower in warm water. I did actually DM an open water class a few winters ago. I took my gear out of the cold pickup truck, hopped in the heated pool, and 20 minutes later had 200 psi more than when I started. How's that for a SAC rate?

The best advice I can give you is to slowly breathe in and out. And breathe deep and fully exhale. Get enough dives under your belt to fully trust your regulator. At that point breathing becomes second nature, much like breathing on the surface.

Learn buoyancy control. Perfect it. Be able to hover motionless for at least a few minutes without changing depth more than a foot either way, using only breathing to vary your depth.

These things you can work on with every dive.

Weighting just doesn't seem to change my SAC rate much. I found a 30 lb weight belt at the beginning of a dive once, strapped it on and hauled that thing around for an hour. SAC rate was exactly the same.

 

[Peter_C]

My advice is just breathe and enjoy the dive. Follow what Gombessa and the others have suggested. Work on your buoyancy by trying to hover motionless and get your trim dialed by moving weight around. Eventually it will all fall together. If you can find a mentor that will definitely help speed the learning curve.

One questions though is, are you getting cold? That will often kick up a persons sac rate.