7 ltr ali or steel for bottom gas

[romperstomper1]

I dived with a 7ltr ali side slung to extend my bottom time ,I found I was very heavy at the start of the dive but on my deco stop only just managed to stay at 6m with 50 bar left .As I expected it also becomes rather floaty.

I'm struggling to borrow a 7ltr steel but would this be a better bet for a side slung bottom gas without having to add extra weight to my belt ?

thanks

[NeilB]

I used to use a 7lt steel cylinder....didn't find it added much weight to my set up. I certainly didn't need to take any off my belt when I used it.

Now I use twin SO40 aluminium cylinders for deco and they do float a little at the end of the dive but not so much I need to put weight onto my belt.

So, to answer your question......if a steel cylinder is going to make you heavier so you don't need to put weight on your belt isn't it going to pull one side down and make you unstable in the water?

Better putting weight on your belt and using a little more air in the BC to compensate at the start of the dive.....the idea is to be neutrally buoyant at 6m at the end of the dive with little gas in your cylinders.

[Twinsetmad]

If your using a 232bar Ali then there isn't much difference in the way it behaves to a steel... full and empty..... I wouldn't bother trying a steel, I bet you wouldn't notice the difference. I've had and used both and am now on 207 bar stages...'
but if your after something thats not floaty, if thats what your worried about then try a 10ltr steel... or strap a 1or 2 kilo block to your stage.

[balbrigganbloke]

I use ali stages here at home but on my recent trimix course we used steel 10s as stages
I had one breathed to about 50 bar and had to drop it off and come back and reattach it 'on the fly'
I dropped it off and put it bottom side down to leave it handy fro me to reattach
I swam off and came back only to find it was upside down,i thought it was the instructor playing games but my buddy said it was the tank itself had done it
So while not as floaty as alis are(and they are) steels do have some buoyancy as well
Phew!!!!!

[Leg Of Salmon]

A 7L, ali or steel, seems a strange choice for a bottom stage.

What sort of bottom time do you get without it?

[The Duck]

... I found I was very heavy at the start of the dive but on my deco stop only just managed to stay at 6m with 50 bar left .As I expected it also becomes rather floaty.

I'd stick with the Ali myself - as mentioned above the 232bar ones are still negitive over all (though only just when nearly empty), it's just the arse end that floats up.

As also mentioned a 7ltr would seem a little small for a bottom stage, I'd personally use an Ali 80 (which do become floaty) or my old Ali 10ltr (which is very negitive all the time), but if it works for you then fine.

[nigelH]

As also mentioned a 7ltr would seem a little small for a bottom stage, I'd personally use an Ali 80 (which do become floaty) or my old Ali 10ltr (which is very negitive all the time), but if it works for you then fine.

Says the man who helped me rethread the weight belt to go on a 12L stage.

I, personally, don't like floaty if it means carrying extra on your belt or harness so I went for loading the cylinders to be neutral on empty (well just a fraction positive). The thinking was I could always pop the belt and send them up the line.

[chrisMc]

Depends what you want to put it in it, air or trimix.

230bar of air adds a few kg in a 7, so either its going to neutral at the start or when empty.

7l 232 ali's are great to manage when full but when empty start to float a lot, especailly when you use He in them. They are also larger than steel.

7l steels are harder to hand off and are negative, but they are a lot more mangeable when you breather them down to 50bar.

Also rember adding weight to your belt compensates overall, but its still ackward to mange when the stage is floating. You should have the stage near bouyant where possible, e.g. nigels example of adding weight to cylinder.

Personally I'd go with 10l steel's. They are compact and carry a lot more gas. Harder to hand over when full, but you can do it with practice. Very easy to mange when you are using them and the pressure gets low.

[chrisMc]

I'd stick with the Ali myself - as mentioned above the 232bar ones are still negitive over all (though only just when nearly empty), it's just the arse end that floats up.

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

[The Duck]

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

Hmm, mine sinks if I let go of it no matter what the calculators say - though I have nitrox in it, never mix.

[Edit: just re-read - completely empty you may be right, not drained a 7ltr to zero in the water]