air consumption

[rubbachicken]

That is a hard quetion to answer. With 155 dives you are no newbie and you say you have your bouancy and weighting down pat. To answer your question we need to know more information:
1. What is your SAC rate now?
2. Diving dry (that will use air) or wet?
3. Normal temp range of your diving?
4. Normal depth?
5. Age
6. Gender
7. What are you doing when you dive? Sightseeing, hunting, photography, working?

Are we talking a SAC of 1.2 SCFM or 0.5 or 0.40 or what? There may not be room to improve. You do have to breath every once in a while.
.

sorry you will have to excuse my ignorance, but what is SAC,
diving dry or wet, i take it that's drysuit or wetsuit, most of my diving has been in relativly warm water 28 degrese C so i wear a full length fleece, but i plan to start drysuit diving in the coldish water here soon, i'm male, 35, no longer a smoker, given up 2 years ago, sightseeing/ protography/ video, and trying to be less chicken an more fish
depth, never more than 32m, seem mostly average 11m to 17m
the last 33 were drift dives, on nitrox, ean 32

 

[pasley]

sorry you will have to excuse my ignorance, but what is SAC,…

http://www.scubaboard.com/t81388-sac_rate_poll_what_is_normal_males_only.html
SAC is Surface Air Consumption Rate. It is a calculation that converts the air used on a dive to the amount of air you would have used at the surface. In that matter you can talk about your air consumption with a standard number. Otherwise you would have to say at 30 meters my air consumption is "x" cubic feet per minute and at 15 meters it is "Y" cubic feet per minute. With a SAC you can just say my rate is "Z" cubic feet per minute. Once you know your SAC you can then do a rough estimate the amount of air required for a dive to any depth by simply multiplying the SAC by the ATA to derive the amount of Air Per Minute we will need. Helps to know if that Al 80 has enough gas in it to get you there, spend 10 minutes and then get you back to the top with some to spare.

Another example. You are diving with a new partner. Your SAC is 0.40 Cubic Feet Per Minute and theirs is 0.60 Cubic Feet Per minute. So now we know that they are using their air 1/3 faster than you are. So if you have an AL80 and they have a Steel 110 you should be just fine and you will both run low on air at about the same time.

diving dry or wet, i take it that's drysuit or wetsuit,…

Exactly. A dry suit requires some of your air thus increasing your air consumption.

…I’m male, 35, no longer a smoker, given up 2 years ago, sightseeing/ photography/ video, and trying to be less chicken an more fish
depth, never more than 32m, seem mostly average 11m to 17m
the last 33 were drift dives, on nitrox, ean 32

So on a dive to 11 meters how long does your tank last and what size tank are you diving?

 

[JDog]

Pasley-Sorry you couldn't make todays dive in Malibu, I thought it was a pretty good one. Have a good week.

 

[Willar]

Let's see if I have this straight.

My SAC rate is .44 and I'm diving to 66fsw (3 ATA) with an 80AL.
.44 X 3 = 1.32 then 80 / 1.32 = 60 minutes total air time.

Or I dive to 4ATA then 45 minutes of air available. Of course this ignores any safety factor for "oh, sh!t, big bull shark!"
Correct?

 

[Charlie99]

Let's see if I have this straight.
..... ...
Correct?

Yes.

 

[jonnythan]

Let's see if I have this straight.

My SAC rate is .44 and I'm diving to 66fsw (3 ATA) with an 80AL.
.44 X 3 = 1.32 then 80 / 1.32 = 60 minutes total air time.

Or I dive to 4ATA then 45 minutes of air available. Of course this ignores any safety factor for "oh, sh!t, big bull shark!"
Correct?

Well... not really, no. First of all, there's 77.4 cf in a full Al80, not 80 cf.

Second, that's the amount of time you have on the bottom before your tank is totally dry.. and that's not a very useful number is it?

Well, be on the surface with 500 psi they say. Well how do you do that? If you're at 4 ATA what psi should you leave the bottom with?

They don't teach this in OW for some reason, but you should know how to do it. Looks like you have your math down. Assume that at the very end of the dive your buddy has an OOA. Are you going to have enough gas to get yourself and your buddy to the surface? Calculate how much gas it takes you and your buddy, both stressed, to do a proper ascent from 4 ATA. This will tell you how much gas to end the dive with.

 

[Uncle Pug]

Well... it would be nice to have a little left over for the ascent too... and the safety stop... or to use correct terminology in the case of 66' for 60 minutes... a deco stop.

 

[Willar]

OK, so I want a 25% safety factor then I could turn at 45 minutes. Of course, I don't always breath a perfect .44, sometimes it's as high as .60 so that would give me 44 minutes before safety factor. At least I have a range to work with now. Thanks.

 

[jonnythan]

25%? That'll leave 750 psi in your tank. Is that enough to get you and your buddy up from 90 feet? Is it more than you need if you're at 30 feet? How do you know?

25% is very random. You already showed that you can do air usage calculations just fine.. so go ahead and do them

 

[jbd]

I did a search and the first few links I found were dead. I did a web search and found this:
http://www.gue.com/classroom/propulsion/index.shtml

With only skin diving experience it looks uncomfortable but I'll look forward to trying it when certified next year. I keep hearing it's a great skill, it must be true.

Pete

Pete,

Its not at all uncomfortable. At first it may seem a little awkward since you are used to the flutter kick. With proper training and a little practice it becomes natural. You just can't beat the efficiency of this kick.