Do I Suck Alot O air?

[The Kraken]

Of course you're going to use more air the deeper you go!
If you use .5 cubic feet of air per minute at the surface, you're going to use 1 cubic foot at 33', 1.5 cubic feet at 66', and 2 cubic feet at 99'.

The volume of air you use and the ATA of your dive are directly proportional:
SAC X ATA = Vol of Air Used. (Where SAC = you surface air comsumption rate and ATA = the atmosphere absolute of your dive)

the K

 

[hudson_hawk]

thank you all
i was on a dive to 60 ft /it was my first dive to that deepth iloved it
it was a shore dive we went out over a wall to 60 ft
we spent about 15 mins at 60 ft
the total dive was 47 mins it was a al80 started with 3000 psi ended with 600 psi
for 17 dives is that usule for a new diver
im just curious i just love it / and yes ill divr divr dive
im taking the aow certifcaton on oct 15 and 16
the instuctor says im ready
thanks again all

 

[The Kraken]

Now this is purely a guesstimate based on the information you've given.
If we use an average dive depth of 35' (because you can't spend the whole dive at the deepest depth) for 47 minutes your SAC rate would be about .64 cubic feet per minute which is pretty normal for a new diver.

the K

 

[WetHoss]

Uhhh, I aint so good with my math, but I come up with 1.36 cfm??

Taking AL80 =80cf/3000psi=.02666cf per psi

600 psi x .02666=15.96cf

80cf - 15.9cf = 64.04 cf used / time(47min)=1.36cfm used??

And wouldn't you multiply the surface CFM by the ATA thereby raiseing the CFM used??

Oops that was the actual CFM used, so it would be less at less average depth....so it would be less than actual CFM...

Am I forgitin somethin???

Hoss'sAss

 

[markfm]

SAC is Surface Air Consumption rate.
http://www.ndc.noaa.gov/pdfs/AirRqmtFormulas.pdf
An AL80 is actually about 77.5 ft3 -- 77.5/3000 = 0.02583 ft3/psi
(3000 - 600) * 0.02583 = 62 ft3 of air used.
The magic is that it's Surface -- 35 ft is pretty close to 2 ATA, so on the surface you would be using 31 ft3.
31/47 = 0.66 ft3/min
(no disagreement with the kraken -- I'm rounding)

 

[WetHoss]

Well, I am confused. If you use .66 ft in a minute at 33 ft, or .66 for three minutes, then you could theroretically get 117.42 minutes out of a tank. If you used 63 cf as in your example then time would be 93 minutes?? What the heck am I missing...


If you are saying that a person uses less that 1 cfm, then they use 62 cf during a dive, they should have more minutes down than cfm used and with a <1 cfm rate that would always be true. If you used 62 cf in 47 minutes, how can that come out to .66 cfm...

Momma didnt raise no dummy but I am mathematically challenged..

Hoss

 

[The Kraken]

Hoss,
He' be using .64 cubic feet at the surface (Surface Air Consumption)
To determine how much air you use at depth you mutliply the SAC rate by the depth in ATA. A dive depth of 33' equals 2 atmospheres, therefore the diver would use 1.28 cubic feet of air per minute at this depth.

An aluminum 80 holds 77.4 cubic feet of air. This diver at a depth of 33' would have approximately 60 minutes of air. At a dive depth of 66' he would have approximately 40 minutes of air.

the K

 

[pasley]

Sounds like you are doing OK. I often dive with new divers and 20-30 minutes is common for the new diver at 30 feet, so you are way ahead of that. Bottom line is, don't worry about it. It is not a contest. Just relax, enjoy the dive, perfect your buoyancy, streamline, move little and slow, exercise and dive often, all of these will lower your air consumption.

 

[Jim Lapenta]

My normal times for an 80 cuft tank at an average depth of 35 ft usually when working with students are approximately 2 dives of 45 min each on air. If I'm just tooling around I can easily get more. If I'm using my hp80's with EAN32 I've gotten 2 1/2 hours worth of dives and still had 500-600 psi left. Looking at my log book on 7/23 using a steel 72 w/air and starting w/3200 psi first dive was to max depth of 54 ft total time 55 minutes.ending psi 2000. 2nd dive to max depth 38 ft w avg of 32ft total time 1:15. ending pressure 650 psi. This tank got refilled. usually if I end up with 800 or more I use that for pool sessions, 1000 psi might not be enough for a decent dive but I can help out in the pool for 2 hrs on that easy since there is usually alot of surface work also. At the beginning I was not that easy on air. But my instructor is really good on air consumption and it's become some what of a contest to see who can safely use the least amt of air. It's helped me immensely to just relax and breathe. I used to suck down an al80 in about 60 min. I haven't dove one in along time since I prefer steel but the lst time I did was around dive number 35 in a drysuit and I got 2 40 min dives out of it in manatee springs and had just over 400 psi left. It all depends on the activity, depth, how relaxed I am, and how good the students are. Bad students mean more work and higher consumption rates. Like when you go "OH CRAP!" and have to chase them down to keep em from doing the missile launch thing or from crash diving to the 90 ft platform cause they forgot to add air. Air conservation measures like proper weighting, streamlining, using the oral inflator when exhaling to add air to the bc underwater and on surface also help out alot.

 

[Xanthro]

Sounds like you are doing OK. I often dive with new divers and 20-30 minutes is common for the new diver at 30 feet, so you are way ahead of that. Bottom line is, don't worry about it. It is not a contest. Just relax, enjoy the dive, perfect your buoyancy, streamline, move little and slow, exercise and dive often, all of these will lower your air consumption.

What Pasley said. LOL.

Really, everything he wrote I completely agree with.