Air consumption

[Yoda-X]

I have almost 100 dives, but hadn't been diving in the 10 years since. Just started diving again and my air consumption on this last week long trip was horrible. Starting to dive a lot, so planning to track it for the next few months.

 

[Storker]

You might see a bit of a tick going from wetsuit to drysuit due to the extra air bubble, but you shouldn't see your winter drysuit going up by almost 1.5x air consumption

If the air bubble adds to the SAC, I should experience at least as much increase between my summer and winter DS config as between the WS and summer DS config. Which is what the numbers say as well. Re-read what I wrote about undergarments. Due to the undergarments, I use significantly more weight in my winter DS. I hardly have an air bubble in my summer DS config.

And 15-17 vs 16-20 isn't a 50% difference.

 

[tbone1004]

14 to 21 is about a 50% increase.
Your air bubble shouldn't be that much bigger and unless you're doing sawtooth profiles it shouldn't be that significant. You're in Norway so in metric.

1l of water =1kg
For the Americans, 1cf of water weighs 62.4lbs
Your drysuit has less than 1cf of air in it, so assuming an AL80, you're going to use max of 3cf of air to inflate the suit to descend to 100ft, 3/77.4=5% of the air in your tank assuming a bit of safety margin. Same in metric, somewhere between 20/25l of air, you have somewhere around 2500l of air in your tank give or take, so 75/2500=3%. Not enough to increase your SAC significantly. What will increase it significantly is the fact that you are breathing heavier because you are cold and somewhat uncomfortable. It's a natural reaction, especially if you're shivering, which uses a lot of O2 since you're muscles are moving when they normally would be relaxed to try to generate heat. That causes your respiratory rate to increase, which increases your SAC, which causes more cold dry air to go into your lungs dropping your core body temp farther, and around and around the circle you go. Stop shivering, slow your breathing down, stay warmer longer, SAC stays the same.

 

[Storker]

14 to 21 is about a 50% increase.

You're comparing best case WS with worst case winter DS.

Your air bubble shouldn't be that much bigger and unless you're doing sawtooth profiles it shouldn't be that significant.

You don't know crap about my profiles. And the SAC data are what they are.

I'll leave my comments to that and refrain from discussing the issue further, since I don't want to completely hijack the thread, and since the thread is in the Basic forum.

 

[BRT]

People who are the most fit have the most ability to convert energy and oxygen into work. When I was 18 I could really do that. Now at almost 60 I could hardly run around my pickup. There are some tiny people who use less air than my wife and I but mostly they seem to be whale shaped people that even I could run circles around.

 

[Texasguy]

This is my guess. It is all about the heart rate, higher the rate, more oxygen one needs (for his body size). If while scuba one gets often influx of adrenaline that keeps the rate up, this translates into more frequent breaths. Thus, even if you might be relaxed, but you are not really at ease, small things often "scare" you for a sec or so, this releases adrenaline, then it translates into faster heart rate and etc. Thus, if one is comfortable enough in the water without getting these flashes of adrenaline surge, one would be able to keep a better SAC. Say, if you feel comfortable scuba diving in that particular site like being in your bed, not many things can provoke you into fight or flight state, you'll keep better SAC. Also, it is about propulsion. If you have soft fins or you use them inefficiently, you have to do more work, thus, more air usage. Might be worth to examine your type of fins and how you kick.

 

[Imla]

When are people going to stop this endless nagging about "need for oksygen"??

Your blood has MORE oxygen than you can possibly need under water!

The driving factor for the frequency of ventilations is CO2!
Breathe properly, expel more co2! CO2 retention also cause an increase in heart rate.

Proper exhalations, efficient fins/kicks for the dive you want to do, and most importantly, planning your available gas vs gasconsumption so that you can actually do the dive you want to do without having to worry about bresthinh this or that way!


Sent from my iPad using Tapatalk

 

[Dirty-Dog]

If you've got good trim, good technique and good buoyancy, then the reality is that you're going to use the gas that you need, and there's not really much you can do that is going to have any significant impact on that rate of consumption.
Without checking logs, I can't be exact, but I've got maybe 450 dives. I'm IANTD Advanced Nitrox/Deep certified. So around here, I'm a noob. I'm a big guy (6'1", 220), reasonably fit, and quite comfortable under water. The math says my SAC rate is pretty much exactly average.
Sue (the blond in my avatar) is a PADI AOW/Nitrox diver with the same number of dives and the same SAC rate.
Kim (the brunette) is a PADI OW diver and will reach 100 dives on our next trip (Cozumel, in October... ). I don't think she actually breathes at all... Her consumption is about like TSandM. I think on most dives, we could just give her a Spare Air and save some cash.

The solution to gas consumption is really pretty simple. Take more gas. You say you're mostly diving on Cozumel (great choice!), so just use an op that provides bigger tanks. Our favorite is Aldora Divers, but there are several shops there that provide big tanks. Aldora uses HP 100 or 120CF steel tanks.
If that's still not enough, get more tanks.
You've got enough dives to know your what your SAC rate is going to be. So just decide how long you want to stay down, calculate how much gas you're going to need, add a buffer, and load up.

 

[Steve_C]

Storker,
you shouldn't see any significant change in your air consumption based on exposure protection provided your dives are the same. You might see a bit of a tick going from wetsuit to drysuit due to the extra air bubble, but you shouldn't see your winter drysuit going up by almost 1.5x air consumption unless you're doing a lot of sawtooth profiles. Lots of people quote water temp as being a factor in SAC rate, but it is purely mental and increasing your respiration rate only makes you get colder faster....

I have a buddy who dives wet and dry. I am always wet. We have found that if we are actually slowly crusiing along it is a lot more work for him to push his dry suit through the water than his wetsuit. Maybe the dry suit is too larger, whatever, it has all sorts of folds and other things that make it not very dynamically clean in the water.

 

[boulderjohn]

I have a buddy who dives wet and dry. I am always wet. We have found that if we are actually slowly crusiing along it is a lot more work for him to push his dry suit through the water than his wetsuit. Maybe the dry suit is too larger, whatever, it has all sorts of folds and other things that make it not very dynamically clean in the water.

My air consumption is noticeably worse in a dry suit as well.