What is average surface air consumption?

[jtivat]

I am 6'6" 235LBS.
My cold water drysuit full tek gear sac. is .7
Warm water is .45

 

[SparticleBrane]

Male, 195lbs, 5'9, 20-years old.
~0.4 to 0.5 normally
0.7 colder water/training situation

 

[Firefyter]

Male, 44yrs. old
6'1, 190 lbs.
wetsuit
.42 average

 

[H2Andy]

back before i quit smoking, i consistely had sacs in the .45 area

once i quit, shot up to .8 and above

now, *if* i don't excert myself i can average .7

if i have to work hard (such as in the Devil's System), it goes back up to .8

 

[Matteo]

back before i quit smoking, i consistely had sacs in the .45 area

once i quit, shot up to .8 and above

now, *if* i don't excert myself i can average .7

if i have to work hard (such as in the Devil's System), it goes back up to .8

isn't that kind of backwards??...you're not giving me a whole lot of incentive to quit smoking

 

[mudchick]

Excuse me if this is a dumb question but how do you calculate sac? Can it be done with a Sherwood Wisdom computer?

 

[Matteo]

Excuse me if this is a dumb question but how do you calculate sac? Can it be done with a Sherwood Wisdom computer?

looking at the Sherwood website, it appears to be a pretty fancy computer...I would be surprised if your SAC rate info was not included somewhere in your dive profile??

 

[H2Andy]

Excuse me if this is a dumb question but how do you calculate sac? Can it be done with a Sherwood Wisdom computer?

it's very easy if you have a computer that gives you the average depth for the dive. i am not sure if the Wisdom does or does ont.

let's assume an average depth of 65 feet for a 40 minute dive.

basically, note how much air you have at start of dive (say 3000 psi) then
note what the end psi is (say 800). that means you used 2200 psi during the
dive.

now, divide the psi used per minutes of dive, and you end up with your depth
consumptio rate (DCR):

2200/40 = 55 psi per minute

now we need to convert to surface consumption rate:

SAC = (DCR x 33) / (Depth + 33)

plugging in our numbers,

SAC = (55 x 33) / (40 + 33)

SAC = 24.8 psi / minute

now, we need to convert that to cubic feet per minute. you need to know the
volume at rated pressure of your tank. assuming an aluminum 80 rated to 72 cubic feet at 3000 psi, that means that each cubic foot is equivalent to 41.6 psi

dividing your SAC in psi (24.8) by 41.6 (how many psis it takes to make a cubic foot of air), you end up with .59 cubic feet per minute.

that means that at the surface, you use .59 cubic feet of air per minute.

now...

you can easily calculate how much air you'll use at any depth by using this formula:

(SAC Rate x (Depth + 33)) / 33

so, with a SAC rate of .59 and a dive to 100 feet, your DCR will be 2.37 cubic feet per minute

in other words, you will use 2.37 cubic feet per minute you spend at 100 feet

 

[riguerin]

The Sherwood Wisdom software (same engine as Aeris) does not provide a SAC calculation. However, the information is stored in an MS Access data base. If you are familiar with MS Access (and relational data bases), it is fairly straightforward to write a simple query to calculate this info. Most of the data already exists ... you'd need to provide some extra info about your tank, however.

 

[H2Andy]

does the Wisdom give you average depth? that's all you need

(well, that and total dive time) (and gas used, but you do that yourself)