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View Full Version : Diving with stages (Ali 80 vs Ali 7)



Keith Wood
28-05-2014, 11:36 AM
Up until last year my normal kit was twin 12ís and 7l 232 bar Ali stage. I use to weight myself without the stage and not change it when I used the stage.

This year I brought an Ali 80 207 bar stage. So far I have not changed my weight. When I used it and breather it down to 145 bar noticed the stage went neutral in weight.

Couple of questions when diving with an Ali 80 stage.

Do I need to add additional weight, when the stage is breathed down to closer to zero since it is more buoyant then the 7L stage?

If I need additional weight would you add it to your normal weight belt etc. or add the weight to the stage?

cheers guys

jturner
28-05-2014, 02:06 PM
Personally, I would weight myself to be able to hold a shallow stop with it all almost empty but then I'm using a CCR and so that extra float will be even more difficult to handle if it wasn't balanced out. That said, it shouldn't be too much on a single ali 80 (there's a calculator around somewhere that no doubt someone will post in due course but a couple of kg only IIRC).

If I was diving OC, I'd definately ensure I could hold a stop with ~20bar in the back gas and a similarly virtually empty stage and the extra weight would go as a vee or tail weight depending in trim requirements. Damn OC setup is hugely overweighted most of the time anyway so an extra kilo or two won't hurt.

Badger
28-05-2014, 02:25 PM
I wouldn't change anything for diving either one or both. But that is based on one particular configuration.

Sent from my super dooper S4 when I should probably be doing somthing else.

Keith Wood
28-05-2014, 02:59 PM
cheers guys with the 7 with about 10 bar and twins with 50 bar i can hold a 3m stop. Not tried it with the ali 80 at 20 bar.

On the next dive with the ali 80 might just add 2 kilo's on and see how it feels. If its to much i try it with a kilo.

gobfish1
28-05-2014, 03:04 PM
cheers guys with the 7 with about 10 bar and twins with 50 bar i can hold a 3m stop. Not tried it with the ali 80 at 20 bar.

On the next dive with the ali 80 might just add 2 kilo's on and see how it feels. If its to much i try it with a kilo.

can i ask why you feel the need for a ali 80 . over a 7 for a one deco cylinder dive ,

Keith Wood
28-05-2014, 03:23 PM
Reasons why i got the Ali 80

It was the same price as the 7.

When i do 2 deco dives per day the reserve for the second dive was getting small. Also after the second dive i can air top and get 50% fill, so if i am diving the next day i do not need to get any deco gas.

If i can not get my twins filled on the boat between dives, i can use the Ali 80 as a bottom gas for the first dive keeping most of my backgas and still deco out on my 2nd stage. Then on the second dive just use the twins and the stage like normal.

Also I am going shetlands in July and we have been told we can only take air and 02 over with us. So taking 2 stages of 02 i can get air tops to make 80% and i do not need to buy any deco gas while away.

Hot Totty
28-05-2014, 04:50 PM
Personally, I would weight myself to be able to hold a shallow stop with it all almost empty but then I'm using a CCR and so that extra float will be even more difficult to handle if it wasn't balanced out. That said, it shouldn't be too much on a single ali 80 (there's a calculator around somewhere that no doubt someone will post in due course but a couple of kg only IIRC).

If I was diving OC, I'd definately ensure I could hold a stop with ~20bar in the back gas and a similarly virtually empty stage and the extra weight would go as a vee or tail weight depending in trim requirements. Damn OC setup is hugely overweighted most of the time anyway so an extra kilo or two won't hurt.

I asked a similar question on mod2 - was told simply weight yourself normally and if you find it difficult to hold stop with light bail out tanks flood or partially flood the unit - it's not working after all ;)

Mark Chase
28-05-2014, 05:24 PM
I use a Al80 for my 50% and if I empty it I can just let it float up on its own. I use a steel 10 for trimix as it floats nickley when full with 18/45 then floats again nicly when empty.

Ask Digger I dangled a floaty steel 10 in front of his nose to prove a point :D

AL80s empty can be a PITA if you need them all the way up.

For shalow dives (50m max) I used two steel 7s because deco was much quicker on 32% and 80% than it is on just 50% and they balance out nicly getting floaty at arround 100bar but not so much they drag you up

You cant realy use a single steel 10 for Nitrox deco as its too heavy on one side which is why I always poped for the 2 7s

ATB

Mark

gobfish1
28-05-2014, 06:42 PM
Reasons why i got the Ali 80

It was the same price as the 7.

When i do 2 deco dives per day the reserve for the second dive was getting small. Also after the second dive i can air top and get 50% fill, so if i am diving the next day i do not need to get any deco gas.

If i can not get my twins filled on the boat between dives, i can use the Ali 80 as a bottom gas for the first dive keeping most of my backgas and still deco out on my 2nd stage. Then on the second dive just use the twins and the stage like normal.

Also I am going shetlands in July and we have been told we can only take air and 02 over with us. So taking 2 stages of 02 i can get air tops to make 80% and i do not need to buy any deco gas while away.

thanks for your reply .
i only ask as i used to dive twin12l,s and could not run up the deco to need a ali80,

most of my time id be on air back gas and deco on o2 and maybe something other ie 57 64 nitrox and id only use 300l or 400l from both cylinder,s of mix, often do two 50m plus dives on one set of 7ls , buddys on ccr so no need for me to look out for them gas wise,

Id rather have a 3l of o2 , than a ali80 of a low pp2 nitrox , i say low as most stops are 12/m and up , on the diving i was doing . or could do on a set of 12ls

3l 5l 7l were my mix of cylinders,

also one deco gas seems to be all your eggs in one place ,

but if your thinking of topping off and the like then maybe the ali80 will do that for you ,

best ,

jturner
29-05-2014, 08:07 AM
I asked a similar question on mod2 - was told simply weight yourself normally and if you find it difficult to hold stop with light bail out tanks flood or partially flood the unit - it's not working after all ;)

Can't be sure if you're joking or not but assuming you aren't, I'd rather not have to go to such an extremity, especially in a hurry and whilst trying to maintain a stop!

Kermit
29-05-2014, 08:19 AM
Can't be sure if you're joking or not but assuming you aren't, I'd rather not have to go to such an extremity, especially in a hurry and whilst trying to maintain a stop!

I've done it before (once). Ascending with a duff unit the CLs can soon max out. It was impossible to maintain buoyancy with full CLs and a less than full bailout tin. Just do it in a controlled manner, not one great big flood in one hit. It seemed quite easy at the time.

jturner
29-05-2014, 08:27 AM
I've done it before (once). Ascending with a duff unit the CLs can soon max out. It was impossible to maintain buoyancy with full CLs and a less than full bailout tin. Just do it in a controlled manner, not one great big flood in one hit. It seemed quite easy at the time.

Apologies for going off topic and asking stupid questions but why didn't you just vent the counterlungs?! I just keep mine emptied on bailing out...

Kermit
29-05-2014, 08:48 AM
Apologies for going off topic and asking stupid questions but why didn't you just vent the counterlungs?! I just keep mine emptied on bailing out...

That's exactly what I did. Perhaps it's down to differences in which unit you are using and, perhaps, terminology. I can only vent the CLs by opening the mouthpiece (which is, of course, not in my mouth). This introduces some water into the loop. This needs to be done on a regular basis on the ascent as the loop volume increases back up to full CLs. So, by venting the CLs I'm partially flooding the unit.

In retrospect this actually makes life a little easier as it also reduces the maximum loop volume.

I dive the unit with just enough weight to keep things under control (just) with a fully inflated loop and a full bailout tin. The rationale being if, in the very unlikely (and never yet needed) event of having to hand the tin off, I can control things as I haven't got a full loop. If I need the bailout gas then I can reduce the volume of the loop by venting/partially flooding.

Hope that makes sense.

jturner
29-05-2014, 11:22 AM
That's exactly what I did. Perhaps it's down to differences in which unit you are using and, perhaps, terminology. I can only vent the CLs by opening the mouthpiece (which is, of course, not in my mouth). This introduces some water into the loop. This needs to be done on a regular basis on the ascent as the loop volume increases back up to full CLs. So, by venting the CLs I'm partially flooding the unit.

In retrospect this actually makes life a little easier as it also reduces the maximum loop volume.

I dive the unit with just enough weight to keep things under control (just) with a fully inflated loop and a full bailout tin. The rationale being if, in the very unlikely (and never yet needed) event of having to hand the tin off, I can control things as I haven't got a full loop. If I need the bailout gas then I can reduce the volume of the loop by venting/partially flooding.

Hope that makes sense.

Yep! Thanks Kermit!

Paul H
29-05-2014, 12:09 PM
thanks for your reply .
i only ask as i used to dive twin12l,s and could not run up the deco to need a ali80,

most of my time id be on air back gas and deco on o2 and maybe something other ie 57 64 nitrox and id only use 300l or 400l from both cylinder,s of mix, often do two 50m plus dives on one set of 7ls , buddys on ccr so no need for me to look out for them gas wise,

Id rather have a 3l of o2 , than a ali80 of a low pp2 nitrox , i say low as most stops are 12/m and up , on the diving i was doing . or could do on a set of 12ls

3l 5l 7l were my mix of cylinders,

also one deco gas seems to be all your eggs in one place ,

but if your thinking of topping off and the like then maybe the ali80 will do that for you ,

best ,

I also use an Ali 80 and a 7 for deco gases and plan for the increased volume in the 80 to ensure I can get out if either of my deco gases become unavailable for whatever reason I.e. a longer deco on 40% when the 80% is cacked (fortunately not happened yet).

It also doubles as a bottom stage for those two dive days where fills between dives are not possible.

Keith Wood
29-05-2014, 12:44 PM
Hi Paul H

Did you increase your weight when you dive with the stages for when they are empty?

Iain Smith
29-05-2014, 01:30 PM
Did you increase your weight when you dive with the stages for when they are empty?

Keith,

An AL80 is 2.65 kg positive when empty. The valve, reg and rigging kit are all negatively buoyant, so you're probably looking at less than 1.5kg positive buoyancy from a completely empty AL80. 50bar of air in twin 12s is 1.5kg.

So, unless you think you're going to be in a situation where you have completely drained your twinset AND completely drained the AL80, I wouldn't bother changing your weighting. (That would equate to having to use the whole of my back-gas reserve AND all of my deco reserve. If I used the AL80 as a bottom stage, then ended up using all of my back-gas reserve to the point that I was feeling "floaty" I'd send the AL80 up my DSMB line to get rid of it.)

Iain

Paul H
29-05-2014, 01:45 PM
Hi Paul H

Did you increase your weight when you dive with the stages for when they are empty?

No. Never felt the overall weight inc valves, regs etc pulling me to the surface. Basically, wot Iain said up there ^^^^

Keith Wood
29-05-2014, 02:08 PM
Cheers guys for your comments. Will give it a go next time i have the Ali 80 low of gas and its a shallow dive.