Any reason to have both double 72's and double al80's?

[Blackwood]

I may be just stupid, but if you put 2 of your 4 80's as a set of doubles, then you have two sets of doubles and 2 single 80's

That sounds like:

Saturday - deep dive with a set of doubles and a shallow with an 80

Sunday - deep dive with a set of doubles and a shallow with an 80

Add in a 30 or 40 for a pony or stage and you are all set for a weekend.

Keeps you from having to run out Saturday night to get your tanks filled.

But I guess everyone else on this list just likes to run out on Saturday night to get the tanks filled, if the shop is still open by the time you get there that is.

How does replacing two of his single 80s with a larger set of doubles change that scenario at all?

 

[Gilldiver]

How does replacing two of his single 80s with a larger set of doubles change that scenario at all?

He takes two of his 80's and makes them into doubles.

Let's see, he has

"a set of double 72's that are my favorite, and I have 4 al 80's."

So he has one (1) set of doubles and four (4) singles. So if he went on a weekend dive, which is two (2) days, where there would be a deep dive - say below 100' and a shallow one in the 20' to 80' range. So right now he would need to borrow a set of doubles or sling two 80's as independents for the deep dive on the second day.

But, if he sets 2 of his 80's as a second set of doubles he now has two (2) days worth of tanks - (a set of doubles and a single) x 2. Sooner or later it comes down to logistics and getting to a boat or remote dive site with all the gas you need for the period of time you will be there helps a lot. The alternative is to try to get tanks filled in the late afternoon or evening of the first day. I have had too many problems over the years in getting this done when I would much rather be having dinner.


I would add the 30 or 40 as a pony or a stage as he see fit because I just like to have them.


Now for some definitions:

Pony Tank: A tank with air or a gas equal to your back gas to be used only in an emergency

Stage Tank: A tank which a diver plans to use on a dive. It should have an appropriate decompression gas called for by the dive plan. As this tank is for decompression, it will most likely have a higher O2 fraction then the back gas.

 

[Blackwood]

But, if he sets 2 of his 80's as a second set of doubles he now has two (2) days worth of tanks - (a set of doubles and a single) x 2. Sooner or later it comes down to logistics and getting to a boat or remote dive site with all the gas you need for the period of time you will be there helps a lot. The alternative is to try to get tanks filled in the late afternoon or evening of the first day. I have had too many problems over the years in getting this done when I would much rather be having dinner.

Allow myself to repeat... myself

How does replacing two of his single 80s with a larger set of doubles change that scenario at all?

 

[Gilldiver]

The original post is:

<<Ok, here is the situation, I have a set of double 72's that are my favourite, and I have 4 al 80's. I've been thinking of setting up a pair of the 80's as doubles as well, but when I really think about the situation, I dont see a time when the al80's would really be any better suited than the 72's to dive with. Anyone have any good reason for having them both?

Jim>>


As we have seen, double 72's and double 80's are just about equal for the amount of gas they carry if you pump the 72's. So no great gain or loss there.

What I am pointing out is that if he gets a manifold and a set of bands for two of the 80's he has two days worth of tanks for the cost of the manifold and bands. If he looks around he should be able to get both for $200 or less.

Now he could go and get a second set of doubles of a size of his choice, but that is just spending dollars that he might not have on two new tanks. Does he want 2 set of doubles and 4 singles or 2 sets of doubles and 2 singles. That is up to him to decide.

Using paid for tanks is much cheaper, but I am just a cheap Yankee

 

[Blackwood]

Ah, I never caught the "for just the cost of a manifold and bands" idea.

 

[DA Aquamaster]

Now for some definitions:

Pony Tank: A tank with air or a gas equal to your back gas to be used only in an emergency

Stage Tank: A tank which a diver plans to use on a dive. It should have an appropriate decompression gas called for by the dive plan. As this tank is for decompression, it will most likely have a higher O2 fraction then the back gas.

I'd expand the stage tank definition a bit.

You can also use it to extend your bottom time.. For example with double 80's, you'd use all of the stage on the bottom first and keep 1/3rd (77 cu feet / 1500 psi) in reserve in the back gas tanks.

Of course that will also probably result in some serious decompression so a deco bottle is probably also needed. Lost gas planning comes into play here. With one Deco gas, you need adeuqate reserve back gas to the much longer deco on back gas. If two deco gasses are used, you need adequate deco gas and reserve gas to do the slightly longer deco on the remaining deco gas and back gas.

So:

Pony Tank: A tank with air or a gas equal to your back gas to be used only in an emergency.

Stage Tank: A tank which a diver plans to use on a dive filled with the bottom mix as the back gas tanks.

Deco Tank: A tank which a diver plans to use on a dive filled with an appropriate decompression gas called for by the dive plan. As this tank is for decompression, it will most likely have a higher O2 fraction than the back gas. The lowest percentage deco tank also often serves as travel gas if you have a hypoxic bottom mix.

 

[Jimmer]

Well I've given it some thought and since I already have a manifold, it really would just be the cost of a set of bands to put these together. So I think I'll do that, dive them a couple times, and if I dont like them, I'll sell them and I'll have manifold and bands ready for a set of hp100's.