How many tanks ?

[KenGordon]

Deco bottles are a bit more personal than you make out. My buddy uses a Faber 10l for first deco, as does another shorter diver I know.

Back to the OP. If you are seriously considering two twinsets maybe you should have a think about a rebreather. Maybe you have the space, a huge truck etc but for me a weekend away that involved two twinsets per diver plus enough deco gas would mean one car per diver and make the logistics much harder.

 

[Superlyte27]

I don't personally like steel tanks for O2. But I don't have a huge disagreement with it. I know it's easier to carry 6 AL tanks than it is to carry 2 Steel and 2 Aluminum as stages or deco.

Personally, if I need more than an AL80 for O2, I'd probably carry 2 AL 80's, rather than 1 Steel.

Ultimately OP, it's going to depend on where you end up. When I was diving Open Circuit, I had about 3 sets of LP85s, 3 Sets of LP104s. 6 AL80, 3 AL40's, and two LP85's for sidemount. Today, I only keep one set of doubles for teaching, and if I had 10 AL80's for my rebreather it wouldn't be enough.

If you get bit with the bug, and really get into tech diving, you're going to accumulate a lot more tanks than what you listed in the post here. At one time I was very near 40 tanks. Today, even with a rebreather I'm over 25, and frankly I feel about 5 tanks short of my needs for some dives. I'm actually borrowing bottles to make the bigger/longer dives.

I think if I were going to start out with 6 bottles. It would be Two LP104's (or the hp equivalent), Two AL80's and Two AL40s. I'd add 80's before anything else. I'd do one long dive per day rather than multiple dives per day so as long as I could fill at the end of each day, I really don't need another set of doubles (yet). But this is based on my situation having access to lots of places to get gas fills.

 

[ajtoady]

Super,,
I reiterate my statement. As seen below, your total based on a LP85 @ 3600psi would be reduced to 90% of your final value. Thus you end up with only 103-104 cu ft.

Up to 200 bar the ideal gas law remains valid and the relationship between the pressure, size of the cylinder and gas contained in the cylinder is linear; at higher pressures there is proportionally less gas in the cylinder. A 3 litre, 300 bar cylinder can only carry up to 810 litres (29 cu ft) of atmospheric pressure gas and not the 900 litres expected from the ideal gas law.

this info is from Wiki gas calculations.

 

[ddmattos]

I think if I were going to start out with 6 bottles. It would be Two LP104's (or the hp equivalent), Two AL80's and Two AL40s. I'd add 80's before anything else. I'd do one long dive per day rather than multiple dives per day so as long as I could fill at the end of each day, I really don't need another set of doubles (yet). But this is based on my situation having access to lots of places to get gas fills.

Fantastic advice!

I'm 5'5" tall. I found the 130's a little too heavy on the surface.

I have the following:
2 sets of 119's xs scuba/worthington
3 Luxfer 80's, looking for one more.
1 Luxfer 40, looking for one more.

This allows me to do two nice deco dives.

When I add a rebreather in a couple of years I could use the 119's as banks when not being dove and the 80's and 40's as bailout depending on the dive. No waisted money.

 

[Superlyte27]

Super,,
I reiterate my statement. As seen below, your total based on a LP85 @ 3600psi would be reduced to 90% of your final value. Thus you end up with only 103-104 cu ft.

Up to 200 bar the ideal gas law remains valid and the relationship between the pressure, size of the cylinder and gas contained in the cylinder is linear; at higher pressures there is proportionally less gas in the cylinder. A 3 litre, 300 bar cylinder can only carry up to 810 litres (29 cu ft) of atmospheric pressure gas and not the 900 litres expected from the ideal gas law.

this info is from Wiki gas calculations.

It's been my understanding that ideal gas law is linear up to 3600psi. That's why I used 3600psi in my calculation. If you know something different, you're going to need to cite something more significant than Wikipedia

 

[tursiops]

Helium really doesn't obey the ideal gas laws at all....O2 is worst (in the range of scuba usage) at around 200 bars, N2 is not so bad.

 

[tbone1004]

and since we are going to 250bar, they behave pretty much linearly, certainly not 10% off. O2 is a little low, N2 is a little high, He is irrelevant for these discussions.

 

[PfcAJ]

I don't personally like steel tanks for O2. But I don't have a huge disagreement with it. I know it's easier to carry 6 AL tanks than it is to carry 2 Steel and 2 Aluminum as stages or deco.

Personally, if I need more than an AL80 for O2, I'd probably carry 2 AL 80's, rather than 1 Steel.

Ultimately OP, it's going to depend on where you end up. When I was diving Open Circuit, I had about 3 sets of LP85s, 3 Sets of LP104s. 6 AL80, 3 AL40's, and two LP85's for sidemount. Today, I only keep one set of doubles for teaching, and if I had 10 AL80's for my rebreather it wouldn't be enough.

If you get bit with the bug, and really get into tech diving, you're going to accumulate a lot more tanks than what you listed in the post here. At one time I was very near 40 tanks. Today, even with a rebreather I'm over 25, and frankly I feel about 5 tanks short of my needs for some dives. I'm actually borrowing bottles to make the bigger/longer dives.

I think if I were going to start out with 6 bottles. It would be Two LP104's (or the hp equivalent), Two AL80's and Two AL40s. I'd add 80's before anything else. I'd do one long dive per day rather than multiple dives per day so as long as I could fill at the end of each day, I really don't need another set of doubles (yet). But this is based on my situation having access to lots of places to get gas fills.

The weight is nice at the end of a long dive. Fluff up that suit, use that tank as an anchor, and chill out. most decos dont require the large volume that steels can afford, so its 'meh' for nearly everyone.

 

[KenGordon]

If doing two deco cylinder dives by the book there are some non obvious (at least to me) implications for cylinder choice. Lost gas scenarios mean you need to be able to deco out on whichever cylinder you have left. This means that a plan calling for only maybe 400l of week deco gas might require lots more if you loose the rich gas.

 

[decompression]

If doing two deco cylinder dives by the book there are some non obvious (at least to me) implications for cylinder choice. Lost gas scenarios mean you need to be able to deco out on whichever cylinder you have left. This means that a plan calling for only maybe 400l of week deco gas might require lots more if you loose the rich gas.

Or, if you've planned for it...share deco gas.


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