GLOC (Online)

Okay, this request was sort of lost in the Ali7 or AL80 thread so I will start it here. Feel free to move it Fundamental questions though....

I will be finishing my TDI Adv EANx and Deco course at the start of March and have bought myself an AL80 following some guidance and recommendations on this board (partly because my normal SAC is approx 20L and as I am unused to deco, my deco SAC won't that far short of that, and partly because an AL80 will come in handly later if I ever get good enough to do Tech 1!)

One thing I am not sure about, however, is how to weight myself for the deco bottle. The worst case has got to be a lost deco gas case. Either shared deco gas with team, thereby emptying your deco bottle making it +3kg bouyant or 2 of the team use deco gas and one decos on backgas and the 2 on deco move to backgas while they hang around until #3 has finished his deco on backgas. Or does everyone stay on backgas to deco....

If, using an AL80, worst case would mean adding 3kg to the weight you normally enter with to be able to hold the stops at the end of the dive.

Now I understand the basics of balanced rig and you should be able to swim up against what you have at the start of the dive, but I carry 5 kg (V-weight and 2 x kg weight belt) to cover me for a set of DIRZONE 12's full of 32%, Ali BP, 10W Salvo & drysuit & fourth element arctics. The gas itself will weigh about 5.5 kgs.

Now this might be where the whole ethos of DIR as a whole comes in, because I shouldn't be diving deco with 32%, but a helium mix which is lighter and therefore the negative bouyancy at the start of the dive is not so much of an issue.

However, as I have said at the start, and in my intro, I am fairly new to this game and would like any information the (much) more experienced people on this board could give me. I will of course raise this with Mark P when I see him, but I would like to know the DIR response.

Thanks in advance.

Gareth

DRE(Offline)

You balance your rig without taking the weight of the stage into account. This means that a full stage will be somewhat heavy (that's what we've got our wings for to compensate, and that's why a lot of people diving multiple stages/deco bottles will use He to get them closer to neutral when full) and an empty stage will be bouyant (not that bouyant that you shouldn't be able to cope with it - don't forget that your reg and guage are also negatively bouyant, so they'll offset some of that weight). In general, you'll never breath a stage bonedry anyway, but if they do become bothersome, you just clip 'em to your upline and let them ride to the surface.
In all my years of stage/deco bottle diving (about 6) I've never been dragged to the surface because of an empty stage, and I dive a SS plate without V-weight with double AL80's and DUI c-2 underwear.

Rich Walker(Offline)

Sort your weighting out for empty(ish) doubles, no stages.

When you get to doing stage deco diving, you'll always be decompresing with a decent amount of backgas anyway, which should offset the weight of the light 80.

If you end up with no backgas, and an empty stage, then you dump the stage and you should still be able to maintain a stop, having wighted for no stages.

Rich

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GLOC (Online)

Thanks Rich, I have the weighting sorted for twins, just didn't know what you were supposed to do with the deco stage.

I suppose it the proverbial hits the fan and you run empty on the stage, run it up the line as DRF says. But that shouldn't happen with the 10% or so contingency...

Thanks again

Diving Dude(Offline)

.....

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Howard

Mal Bridgeman(Offline)

Surely, if it's a genuine question, it's ok to ask?

BTW you can set your own tagline here it seems, From "Quick Links" choose Edit your profile.

HTH
Mal

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GLOC (Online)

Lost....

Howard, was yours a geniune question, or was it mine you were querying....as I don't have a troll tagline.

davy(Offline)

No no no...
It's not that bad...

An AL80 is about 2.5 kg positive when empty without a valve and regulator...
With a valve, regulator and stagekit attached to it it will be slightly positive when empty.

If it's too heavy when full... add helium :D

GLOC (Online)

Thanks Davy for that, forgot about the valves and regs.....

For that I would need to have some Trimix ticket, some way off I think....

clarktenk(Offline)

I second that and it brings up proper tank selection for newby divers that you should really look into buoyancy characteristics of the doubles you will be putting together. Once you know what your getting or already have you need to spend some time in a quarry/pool environment getting your weighting right. This is too often a step that intro tech divers skip and probably one of the most important to start with. If you aren't diving a balanced rig you simply create more problems as you progress through the ranks.