Improving my air consumption

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I have heard split fins add air to your tank! Thats why Freedivers have seen the light and now diving to well over 1500ft using split-fins! I heard of a diver in Laguna beach who was using split-fins and kicked twice only to find he had run into the Avalon Pier! Cavers are now going to split-fins and single 80's and getting four hour dives! Thank god for the inventor of the greatest modern invetion of all time! NASA is trying to use the same technology to power the space shuttle!
:rofl3: ... best post of the thread ... :D

... Bob (Grateful Diver)
 
I also never ever inflate my BC at all during a dive, unless it's absolutely necessary. I'm not sure how much air I save doing this. I have my weights set just right so that when I dump all the air out of the BC, I slowly sink down, and throughout the dive I only use my breath to fine-tune my buoyancy and hover at any depth.
Let's say you have add enough air to your BC to offset 32 pounds of negativity. For many people, that's an astoundingly large amount (I don't even need that much if I completely flood my drysuit at the very beginning of a dive while wearing super-thick fleeces), but if you're a big person in a really thick wetsuit on a deeper dive, it may be closer to life. Anyway, how much air did that huge amount of buoyancy cost?

Well, 32 pounds works out to half a cubic foot of standard seawater. Let's say that you were at 100 fsw. That's a pressure of 4 ata, meaning that you'll draw 2 standard cubic feet of air from your cylinder to have the 32 pounds of buoyancy. If you're using an 80 cubic foot cylinder with a service pressure of 3000 psi, 2 cubic feet is a pressure equivalent of... 75 psi!

Of course, another way to look at it is by "air time". If you have a respectable air consumption rate of 0.5 cubic feet per minute, that 32 pounds of buoyancy is equivalent to... yep, one minute at that depth. (If you add air until reaching 100 fsw with 32 pounds of buoyancy, you'll have used the amount of air you'd breathe in one minute at 100 fsw.)

You will almost certainly burn through more air holding depth due to not being neutral through the entire dive than you would save by trying not to use a BC to maintain coarse neutrality. (Fine changes are, of course, from the lungs.)

The only time I've seen BC gas have a significant effect on my gas consumption was on a dive where I spent a good amount of time at 55 fsw doing drysuit and wing practice with a new drysuit and wing diver. We spent the entire time adding and dumping, and it glaringly showed on the SAC computations, but that's not at all the way any moderately decently skilled diver would actually dive.
 
I was diving last week in Roatan and our average dives were to 60 feet with a dive time of 50 minutes and I would end up with 700 to 800 PSI left, however if I didn't take my camera with me I would have 3 to 4 hundred lbs more. Taking pictures would not seem like a lot of tasking but obviously it is.

Bruce
 
I was diving last week in Roatan and our average dives were to 60 feet with a dive time of 50 minutes and I would end up with 700 to 800 PSI left, however if I didn't take my camera with me I would have 3 to 4 hundred lbs more. Taking pictures would not seem like a lot of tasking but obviously it is.

Bruce
YMMV. Others have reported that bringing a camera along improves their SAC, since with a camera in hand they tended to slow down and look more closely at the small things around them.

My observations on SAC are:

1. If you are working hard, then you need to breathe a lot to clear out the CO2. The secret to having low SAC is avoid working hard.

2. If diving is hard work, then you are most likely doing something wrong.
The most likely candidates are:
1) You aren't neutral and are going around negatively buoyant while continuously finning upward to maintain depth.
2) You are not horizontal. Moving through the water is much easier if you are horizontal.
3) You are inefficient. Using your hands to propel yourself or adjust depth is inefficient (you have those big monster fins on your feet for a reason). Your finning technique may be lacking.
4) You are going too fast. If you slow down, your SAC will come down. Long ago I found that that, outside of things like coral, sea stars, and sea cucumbers, pretty much everything down there can easily outrun me.

3. My personal experience is that cardiovascular fitness does not affect my resting SAC, but improved fitness greatly reduces how fast my SAC rises as I work harder. In other words, fitness level doesn't affect my SAC for slowly puttering around the reef, but good fitness level helps reduce my SAC when doing a long swim at 1 knot. (This is my personal observation only. There doesn't seem to be a general consensus on this)

4. Your SAC at any given point in your dive history is what it is. Plan your dives for what your SAC is rather than what you wish it would be. Don't be any more embarrassed about your SAC than you are about your height. It is what it is.

5. Step one is to reduce your workload. Only after that does it make sense to pay much attention to breathing. For me, I find what works best is very long inhale/exhale cycles, with a large portion of the cycle spent with lungs near full. Personal observation. Sample size of 1.

6. SAC follows a typical learning curve cycle --- rank newbies have very high SAC which rapidly falls as they learn to be able to get neutral so that they can stop finning and stay where they are. After than, the SAC reductions come more slowly with such things as improved finning techniques.
In general, you don't lower SAC. You change how you dive and that affects your SAC. SAC is not a goal unto itself.
 
Only 11 dives under my (weight)belt - still, here are my 2 cents:
1. Buoyancy - I improved my bottom time from one day to the next (literally!) just by finding out how to be able to relax and not squandering energy and breath on staying buoyant
2. Fitness - I used up my tank slightly slower than my husband, who is slightly less fit :-P
3. Most importantly tho... my guess is that experience is the real key - when me & hubby extended our bottom time and still surfaced with a lot more left in the tank than on previous dives (about 50 bar), proudly bragging while climbing back into the boat, our DM just laughed and showed us his SPG... 160 bar left :-)
 
While everyone is answering this question, I have a related one....what is a better indicator: SAC rate or psi/min?
SAC rate. PSI/min is useless except for at the depth it was measured at, using the same tank. SAC is basically PSI/min adjusted for depth and tank size.
 
YMMV. Others have reported that bringing a camera along improves their SAC, since with a camera in hand they tended to slow down and look more closely at the small things around them.

My observations on SAC are:

1. If you are working hard, then you need to breathe a lot to clear out the CO2. The secret to having low SAC is avoid working hard.

2. If diving is hard work, then you are most likely doing something wrong.
The most likely candidates are:
1) You aren't neutral and are going around negatively buoyant while continuously finning upward to maintain depth.
2) You are not horizontal. Moving through the water is much easier if you are horizontal.
3) You are inefficient. Using your hands to propel yourself or adjust depth is inefficient (you have those big monster fins on your feet for a reason). Your finning technique may be lacking.
4) You are going too fast. If you slow down, your SAC will come down. Long ago I found that that, outside of things like coral, sea stars, and sea cucumbers, pretty much everything down there can easily outrun me.

Good observations.

lil bit:
3. My personal experience is that cardiovascular fitness does not affect my resting SAC, but improved fitness greatly reduces how fast my SAC rises as I work harder. In other words, fitness level doesn't affect my SAC for slowly puttering around the reef, but good fitness level helps reduce my SAC when doing a long swim at 1 knot. (This is my personal observation only. There doesn't seem to be a general consensus on this)

Works this way for most people. the more fit you are,the less out of breath you are (on the surface) when exercising hard. Out of breath=breathing harder=higher SAC.

lil bit:
4. Your SAC at any given point in your dive history is what it is. Plan your dives for what your SAC is rather than what you wish it would be. Don't be any more embarrassed about your SAC than you are about your height. It is what it is.

5. Step one is to reduce your workload. Only after that does it make sense to pay much attention to breathing. For me, I find what works best is very long inhale/exhale cycles, with a large portion of the cycle spent with lungs near full. Personal observation. Sample size of 1.

6. SAC follows a typical learning curve cycle --- rank newbies have very high SAC which rapidly falls as they learn to be able to get neutral so that they can stop finning and stay where they are. After than, the SAC reductions come more slowly with such things as improved finning techniques.
In general, you don't lower SAC. You change how you dive and that affects your SAC. SAC is not a goal unto itself.
 
Only 11 dives under my (weight)belt - still, here are my 2 cents:
1. Buoyancy - I improved my bottom time from one day to the next (literally!) just by finding out how to be able to relax and not squandering energy and breath on staying buoyant
2. Fitness - I used up my tank slightly slower than my husband, who is slightly less fit :-P

A lot of this is due to your having smaller lungs than your hubby. If a man and woman of equal experience and fitness dive together, the woman usually uses a whole lot less air.
3. Most importantly tho... my guess is that experience is the real key - when me & hubby extended our bottom time and still surfaced with a lot more left in the tank than on previous dives (about 50 bar), proudly bragging while climbing back into the boat, our DM just laughed and showed us his SPG... 160 bar left :-)


Yep. Experience (because of both increased calmness, and better technique) usually results in much better air consumption.
 

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