Muscle mass and air consumption

[DivingDoc]

I've attached a picture of Ralf with us in Grand Turk. In order from left to right:

my husband, Ralf Muller, me, Lorenzo Lamas (wearing my son's wetsuit), Lorenzo's daughter, and my son.

To put things in perspective, my son is 5'9"; I am 5'4".

You can see pictures of Ralf in Gladiator at these web addresses:

http://www.spielberg-dreamworks.com/gladiator/presskitgallery/Slave_Army.jpg

http://www.spielberg-dreamworks.com/gladiator/presskitgallery/Battle_Victory.jpg

 

[steeldiver]

Hey its early,
YOU GUYS SHOULD USE METRIC SOOO MUCH SIMPLIAR TO DO CALCULATIONS.
A sac RATE in litres/min of under 10 is qualified as acceptable
any thing under 6 is rated good.
I;ll get out my conversions and do the maths in imp.
AS our water is quite cold the dive times are relatavly short
the average diver usually finishes his dive with plenty air to spare
The cold has a negative effect on visitors and firstly diving with full
protective gear and secondly the water temp
shhoots their sac rates down in flames.
your sac rate should only be used as a guide and on any given day can double caused by one of many factors
HOWARD

 

[Hoppy]

Oh I wish !!!!!!!!!!!!!!!!!!!!!!!!!!

I'm the original Hoover then :upset:

From experience my SAC goes through the ceiling when I'm not relaxed.

Cold doesn't seem to matter.

Just two pennies worth.

Hoppy

 

[KyPete]

At 6'2" and 245lbs with a somewhat balanced amount of fat and muscle, I find that air consumption on my first dive of the trip is by far the worst. From the second dive on, I go from being a hoover to just "not good". My general theory is that relaxation and general fitness are somewhat equally important.

To combat my air sucking, I make sure I'm completely relaxed before descending (especially if the water is cold); use my snorkle exclusively on the surface; and, force myself to rest on the bottom (sand) periodically during the dive. Also, I let my dive buddy know that I will probably be out of air before him, so he can decide if he wants to surface, join someone else, or go it alone for the last few minutes of the dive.

 

[DivingDoc]

What does the "S" stand for in SAC rate?

How does one calculate one's SAC? Obviously, it's going to vary during the dive -- more during exertion and with deeper depth, etc. I guess we're talking about average for each dive?

I know what my starting and ending PSI's were on a dive and the length of the dive in time. How does one go from there to L/cu meter or whatever the units are?

Thanks.
ET

 

[ibnygator]

DivingDoc once bubbled...
What does the "S" stand for in SAC rate?
How does one calculate one's SAC? Obviously, it's going to vary during the dive -- more during exertion and with deeper depth, etc. I guess we're talking about average for each dive?

Let me preface all that follows by saying I am no expert. In fact, I stated in my post that this is new to me so I'll pass on what I have learned. Please, anyone, correct any mis-statements on my part.

Surface Air Consumption = the volume of air consumed divided by the average atmospheres absolute divided by total dive time.

Volume of air breathed = ((Starting PSI - Ending PSI)/100 )* (tank rated volume/tank rated pressure*100)

Average ATAs = (average depth of dive/33) + 1

So for example: if you use an AL80, start with 3000 psi and end with 1300 psi on a 27 minute dive with an average depth of 45', the calculation would be:

((3000-1300)/100) *(80/3000*100) / (45/33 +1) / 27 = .71 cubic feet per minute

Whew...I'm sure I blew the math somewhere, but I hope that helps.

:think:

 

[ChrisF]

ibnygator once bubbled...


...snip

Volume of air breathed = ((Starting PSI - Ending PSI)/100 )* (tank rated volume/tank rated pressure*100)

Average ATAs = (average depth of dive/33) + 1

So for example: if you use an AL80, start with 3000 psi and end with 1300 psi on a 27 minute dive with an average depth of 45', the calculation would be:

((3000-1300)/100) *(80/3000*100) / (45/33 +1) / 27 = .71 cubic feet per minute


:think:

You're making it more complicated that it needs to be by dividing and multiplying by 100.

Volume of air breathed = (Starting psi - Ending psi) * (Tank Volume/Tank rated pressure)

Also, the volume of a standard AL 80 is 77.4 ft3; not 80. So to get your SAC based on air consumption at a particular depth you can use:

(starting psi - ending psi) * 77.4/3000
-------------------------------------------------
Dive Time * (depth/33 +1)

or

(3000-1300)*77.4/3000
-------------------------------------- = .69 ft3/min
27 * (45/33 + 1)

If I had used a tank volume of 80 ft3, this forumula should yield the same result as you had above.

 

[ChrisF]

steeldiver once bubbled...
Hey its early,
...snip
A sac RATE in litres/min of under 10 is qualified as acceptable
any thing under 6 is rated good.

By my calculations 10 liters/min is .35 ft3/min.

That's pretty darn good. My SAC rate is closer to .5 ft3/min and that's on a good day. You must be part fish

 

[ibnygator]

ChrisF once bubbled...
You're making it more complicated that it needs to be by dividing and multiplying by 100.

Volume of air breathed = (Starting psi - Ending psi) * (Tank Volume/Tank rated pressure)

Also, the volume of a standard AL 80 is 77.4 ft3; not 80

You're right, I did make it more complicated by dividing and multiplying by 100, but I was attempting to be as detailed as possible to show the derivation of the formula. Thanks for the correction on the AL80 volume.

But my original question still stands, is that a decent SAC rate, or am I an ignorant hoover?

 

[Newhampster]

.59 to .7 strikes me as decent but it depends on conditions. Under some conditions (and equipment and other variables), it's great; under others, it's a bit high.

Consider:

If you're diving in green water, high current, swell, with a wicked thermocline (and lotsa neoprene) and carrying a few extra cylinders under your arms, then... you'll consume a lot more air than if ... you're doing photography in the carribean and laying in wait on the bottom at 60 feet with no current, just watching some gobis waiting for them to arrange themselves the right way...

Under the former conditions, 0.6 sounds great to me. Under the latter conditions, 0.6 is a bit high.

The real question is whether your air consumption is OK vis-a-vis your dives (and your buddy's air consumption). If you both have about the same rate, and you both come up with at least 500 psi left when you surface, u be cool.

I don't consider myself great on air consumption. Just a bit better than average which is nothing to crow about.

I typically run 0.45 to 0.60 depending on conditions, equipment and other variables. When I started diving, my SAC was way over 1... My 'personal best' is 0.42.