Deco Bottles- 30cf vs 40cf?

[rongoodman]

I'd get a 40 rather than a 30, and keep an eye out for Al72s for when you need something bigger. A sidemounted 40 worked very nicely for a bailout bottle in my CCR course.

 

[Superlyte27]

Get a 40.
I bought LP45's and 50's. When I'm carrying 6 or 7 bottles the LP tanks seem super heavy.
I've been on dives where my dive plan called for 26cu' of O2. Even if you plan a minimal 1.2x your need for reserve, a 30cu' cylinder would be too small. And if you're going with some agency's recommendations of having 1.5x the necessary gas, then a 40cu' just barely makes it. Certainly we could draw the line anywhere, but when you figure in that a 30 dives exactly the same as a 40, why bother. They cost the same, feel the same, but the 40 holds more, buy the 40.

 

[PfcAJ]

1.2x? Why 1.2x? Thats new.

 

[lindenbruce]

Exactly what TSandM said. 40's you wont even notice. With 80's you will feel the added width. It's not a bad sensation, just there. But you will sure love having the gas if you ever need it. B.

 

[MalibuJerry]

1.2x? Why 1.2x? Thats new.

A new one for me too. If you have enough for yourself and enough for your team mate were he/she to lose their gas then you need 2x plus a slight margin.

You will not notice the difference in the water between the 40's and the 30, so go with the 40's.

 

[PfcAJ]

2x is equally new.

 

[Peter69_56]

I have 2 x 40, 1 x 70 and 4 x 90 with back gas of 2x 100

I prefer 40 as sling as they have sufficient capacity without being bulky. The 70 is used as an additional gas for longer deeper dives requiring additional deco but is somewhat larger.

I also have a baby 20 which I use with rec diving (mainly for others and training rather than any real practical use)

 

[Superlyte27]

1.2x? Why 1.2x? Thats new.

Its not new. It's old. When I get to a laptop I'll cut and paste the agency's standard.

 

[PfcAJ]

Does the standard include the reasoning behind it? After thinking back a bit, I think I remember this from an IANTD thing, and no reason was given in the text.

 

[Superlyte27]

1.2x? Why 1.2x? Thats new.

I don't have my laptop here with the link I wanted to give, but anyway. There's some literature out there stating to plan 1.2 instead of 1.5, because your sac rate decreases significantly during deco, and worse can scenario, you should have enough back gas to complete deco in the event that you didn't have enough deco gas. So, 1.2x your need, instead of 1.5. I'm not sure I agree or disagree. I really don't care either way, but was using it to back my argument for an AL40 over and AL30

---------- Post added August 2nd, 2013 at 09:54 PM ----------

Does the standard include the reasoning behind it? After thinking back a bit, I think I remember this from an IANTD thing, and no reason was given in the text.

Ahh, you have a good memory. It was IANTD. And I don't remember if a reason was given, but I asked Tom specifically about it and was given the info I posted above.