7 ltr ali or steel for bottom gas

[Simon A]

This isnt true, an empty 7l will float (unless you strap lead to the side). If you have 80bar of air and regs attached this may be the case, but 40bar of trimix, if you let go it will be on the surface.

I have a bouyancy calc for cylinders sheet (created by someone else) if you want a copy sned a pm with your e-mail and I'll send it over.

7l ali
Buoyancy Fresh
Full Empty
-0.63 1.46

Buoyancy Salt
Full Empty
-0.32 1.77

Chris,
This may or may not be the case, Old ALi 7's at 8.8kg do float, but in my experience the new Ali 7's at 9.8kg do not. They go arse light when empty but are just negatively buoyant.

If the OP has the older ali 7's he may wish to try the new style as a compromise. (8.8kg ali 7L's in test are very easy to sell on)
HTH
Simon A

[nigelH]

My calculator is to simple to be a calculator

[neilh]

I have a bouyancy calc for cylinders sheet (created by someone else) if you want a copy sned a pm with your e-mail and I'll send it over.

Lots of statistics as well as photos here as well: Images of all our cylinder characteristics | Silent Planet

[romperstomper1]

As also mentioned a 7ltr would seem a little small for a bottom stage,

It is to be used with a 15 ltr so gives me similar gas to a twin set ,think maybe a 10 would be to big side slung on its on .

thanks for the replies

[Tunicates]

Similar to what I'm using then.

This year I've bought my own 15 singles and an ally 40 (gives 5.6L) that gets used on dives @ 30m, balanced by having an extra 1k on the other side of my belt.

I use it as a big pony, but also to extend my bottom time.
I'm not using it for different mixes and I assume your not either, it generally has the same as whatever my back gas is - often 32% (or 30% depending on where it gets filled )

If I breath it as bottom gas then yes, it gets floaty at @80 bar.
If I start breathing off it only on my ascent (at 80 or 90bar on the 15) then even with 10 mins or so of deco I still have @150bar in it on surfacing so it never gets anywhere near being floaty.
Everything stays nicely balanced, and I end up finishing the dive with a 3rd gas remaining.

Seems to work ok.

[romperstomper1]

Similar to what I'm using then.

I'm not using it for different mixes and I assume your not either,

I will only be using it for the deeper dives 40-50m so it will contain air but I have a 50% mix in my pony for deco .

[Tunicates]

Thats me shown then.

I'm liking the use of a smallish stage and single 15L though.
I dont know cos I havent used a twinset ever, but it seems a very versatile system.

[romperstomper1]

Thats me shown then.

I'm liking the use of a smallish stage and single 15L though.
I dont know cos I havent used a twinset ever, but it seems a very versatile system.

Yep thats what I like ,just clip it on when you need it ,I found a twin set was like carrying a small house on your back not ideal down or up a slippery slipway at low tide more suitable for hard boat diving imo .