Question about changing tank size to accomodate air consumption rate.

[Blue Sparkle]

(On the secondary topic of the thread....)

Too frivolous, I'm sure

 

[fnfalman]

Just to clarify: Right now I don't have any preference in tank size. I asked the question because a dive op suggested an AL63 to me, and I've since read threads here wherein a smaller or larger tank was recommended to someone for consumption/size reasons.

Then, on the other hand, I had spoken with someone who mentioned the "buddy gas" concept, and how you are carrying your buddy's spare air; and from that angle it seemed that the opposite would be true (that is, the "sippier" diver would not carry less air).

So, I started the thread to hear what people have to say on the subject and then to be able to make an informed decision if the tank-size-option comes up again

B.

My suggestion is to carry as small of a tank as you can get away with. If I don't think that I'd need the HP100 (air hog), you can damn well be sure that I won't be lugging it.

Figure out your SAC rate, have your buddy figure out his or her SAC rate and do a calculation of how much air you BOTH would need to go from maximum rec depth of 130ft to surface and do a 3-minutes safety stop. Include that volume of air needed into your gas planning for your turnaround PSI.

If something drastic were to happen, all you need is enough air to get both of you up to the surface in a fairly quick manner. Not quick enough to risk lung embolism or the bend, but you're not going to do the 15-ft/min ascension, that's for sure. If you were to want to do the proper ascension, safety stop, blah, blah, blah, then start thinking about slinging a pony bottle. But if you just want to know how much air to safely get the both of you to the surface, you'd be surprised that it probably wouldn't be that much once you calculate it out.

Once again, let's reiterate that you are not doing technical diving so that people aren't going to start telling you about stage bottles, deco time, and this or that. If something happens, you and your buddy share air and head straight to the surface.

 

[TSandM]

You know, I don't get the weight difference thing. I'm 55 years old, 5'4" and have never in my life been considered anything close to athletic. I started diving in Puget Sound with LP95s. They're heavy. At first, lugging them around was a PITA. Nowadays, it's not. No gym time involved; I just kept lugging them, and eventually added a scooter, and then doubles, and then doubles and a deco bottle, and then doubles and a deco bottle and a scooter . . . Like the guy lifting the calf every day as it grew, I got stronger!

When we go to Maui, the dive op always forgets and tries to talk me into a 63. I just shake my head and politely say, "No, thank you," and go do my 90 minute dives -- with my husband, who is also on an 80.

Using a tiny tank when that's all you need is probably delightful. I enjoy it in the pool. But for a "real dive", using a tank that allows a dive long enough for you to enjoy it seems like a very reasonable idea to me.

 

[fnfalman]

By all means, carry a tank large enough to support your bottom time.

But if you were to know that you're not going to be underwater for more than, say, 45-minutes (that's all you would want to spend underwater for whatever reasons) and taken your SAC rate into account, taking your gas planning into account and the final calculation calls for a 80-cuft tank. Why would you want to pack a 100 or a 120?

 

[Blue Sparkle]

I agree with you both

On the specific dives I was doing, the max time we were allowed to be off the boat was an hour, and it was possible to surface anywhere, so it sounds like I could have enjoyed the "nimbleness" of the AL63 with no penalty.

OTOH, if dive time were less limited, then I would not have wanted to limit my time just to have a "sportier" tank.

I now understand more about how/when changing tank size is a sensible option, and why I had heard that it was not a good idea (sounds like that is more for restricted environments and/or much deeper dives where ascent times are long).

Thanks!

B.

PS: And in my specific situation (although I was asking the question in a general sense), I think it would have been nice if my dive buddy could have used a larger tank. I say that because we were surfacing a bit early (on some of the dives) so that he would get back to the boat with 500 psi. If he'd had a larger tank, we could have stayed out the full hour. If that situation occurs again, it would be worth checking into renting a larger tank.

 

[redacted]

I agree with you both

On the specific dives I was doing, the max time we were allowed to be off the boat was an hour, and it was possible to surface anywhere, so it sounds like I could have enjoyed the "nimbleness" of the AL63 with no penalty.

OTOH, if dive time were less limited, then I would not have wanted to limit my time just to have a "sportier" tank.

I now understand more about how/when changing tank size is a sensible option, and why I had heard that it was not a good idea (sounds like that is more for restricted environments and/or much deeper dives where ascent times are long).

Thanks!

B.

PS: And in my specific situation (although I was asking the question in a general sense), I think it would have been nice if my dive buddy could have used a larger tank. I say that because we were surfacing a bit early (on some of the dives) so that he would get back to the boat with 500 psi. If he'd had a larger tank, we could have stayed out the full hour. If that situation occurs again, it would be worth checking into renting a larger tank.

Another alternative is to balance your gas during the dive. My wife and I have fairly compatible SACs but we do occasionally get a little out of balance especially if one of us starts with a short fill. So we will even out the gas supply during the dive. Typically we do this later in the dive as we are working our way up from our max depth but well before the low tank gas supply falls below 1000 psi. It extends our dives a bit and gives us a good training opportunity.

 

[fnfalman]

Another alternative is to balance your gas during the dive. My wife and I have fairly compatible SACs but we do occasionally get a little out of balance especially if one of us starts with a short fill. So we will even out the gas supply during the dive. Typically we do this later in the dive as we are working our way up from our max depth but well before the low tank gas supply falls below 1000 psi. It extends our dives a bit and gives us a good training opportunity.

Damn good idea. My regular dive buddy and I use same tank capacities and have pretty much the same SAC, but for some reasons he was sucking some serious air this last outing. He was hitting turn-around PSI (1500psi) and I was still around 2200-psi, so instead of heading back, we shared air and stayed a few more minutes goofing off in the kelps until I hit 1500psi then we headed back.

We did it twice until the third dive where his air consumption somehow went back to before.

 

[aquaregia]

Another alternative is to balance your gas during the dive. My wife and I have fairly compatible SACs but we do occasionally get a little out of balance especially if one of us starts with a short fill. So we will even out the gas supply during the dive. Typically we do this later in the dive as we are working our way up from our max depth but well before the low tank gas supply falls below 1000 psi. It extends our dives a bit and gives us a good training opportunity.

So you just share air for a bit, or you have a tank equalizer that you connect... between the 1st stage HPs?

 

[idocsteve]

So you just share air for a bit, or you have a tank equalizer that you connect... between the 1st stage HPs?

Wow

This is how great ideas are born!

Idoc runs to beat aquaregia to the patent office

 

[redacted]

So you just share air for a bit, or you have a tank equalizer that you connect... between the 1st stage HPs?

Just share air.