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  1. #1
    Established TDF Member JimmE's Avatar
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    Anyone dived twin Ali 12's?

    So, most of my UK diving is on twin 12's (steel).

    I'm looking at a possible live-aboard trip next year with blue-o-two ( a mixed group of single-clyinder Rec divers, one or two on CCR and a handful who will likely go with twindies) and see they offer rental of manifolded Ali 12's. (Ali 80's?)

    Would be looking at doing max 45m, nitrox, just after longer dives. Just wondered if anyone had dived with this set and how it compared (weight-wise) with steels?

    I'd imagine they'd be rather buoyant when closer to empty?

    With steel 12's I use a 3mm steel backplate and an extra 4kg weight belt.


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    Last edited by JimmE; 28-04-2017 at 09:09 PM.

  2. #2
    Coastal Member dwhitlow's Avatar
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    first dive just jump in with the amount of lead that seems too much and afterwards drain the tanks down and do a proper weight check.

    You know there is no other way and you'll be glad you did for all the following dives.

    That is exactly what my buddy and I did on the last visit to the Red Sea (2009). Oddly, we were the only ones who did so and it was pretty obvious all week that some of the others were very heavy.
    Last edited by dwhitlow; 28-04-2017 at 08:48 PM.

  3. #3
    Established TDF Member Steve Clark's Avatar
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    You can work it out here :

    https://www.subaqua.co.uk/cylinder-buoyancy.php

    You will need about 5kgs more weight for twin al80s than 232 bar steel 12's, everything else being equal (suit etc.)

    Edit : you should think carefully about the balance of ditchable vs. non-ditchable weight and consider the effect of depth of wetsuit buoyancy. Or wear a drysuit
    Last edited by Steve Clark; 28-04-2017 at 10:26 PM.

  4. #4
    Owner and Lead Instructor at Underworld Lanny's Avatar
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    I do hundreds of dives every year in twin Al80s, which is probably what you will get from Blue O2 - it is what they have always given me when I requested a twinset, although it is a few years since I dived the Red Sea. The weight you need will obviously depend on your exposure suit, but to give you an idea, I use a small 2kg tail weight and a steel backplate with a drysuit and thin (Xerotherm/PBB) undersuit. I am a former prop forward - 6 feet and around 100kg. You are right that Al80s get a bit floaty at the bottom when empty. The buoyancy "swing" actually happens at around 140 bar.

    If you are diving wet, you are unlikely to need any weight, but may want to add some tail weight to help trim and offset the floaty tail. An easy way to do this is to wear jetfins or similar heavy fins. You can also improvise a tail weight by tying some cave line (string!) through the hole in a normal block weight and looping it over the bottom bolt of the twinset. Be careful that this does not overweight you - I would use an aluminium backplate if you are diving wet and make sure you are balanced. They normally do a check dive on Blue O2 boats - ideal chance to drop the pressure to 35 bar and see how your weighting is.

    Have a good trip!
    Lanny
    Living the dream in the Mexican Caves
    http://www.underworldtulum.com
    http://www.cavecamp.com

  5. #5
    Established TDF Member
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    I dive twin Ali 80, wet.

    Ali backplate, 40lb wing, ~3mm suit (was a 5mm but it's old and compressed now) jetfins.

    With old canister lamp / NiCd battery pack I pretty much didn't need any additional weight.

    Now have a halcyon focus and the battery pack is tiny so use a 2lb weight to trim.

    Seems to be about right.

  6. #6
    Established TDF Member JimmE's Avatar
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    Sounds good - thanks all, sounds like it might be simpler than I expected.

    I guess they are widely used around the world so makes sense, but given that I usually find I need more weight than I expect for a single ali-12 (hence tend to prefer a steel 15 if available) perhaps I was over-thinking it.

    Cheers!

  7. #7
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    Al80s are 11.1-11.4L and are roughly 2kg negative when full with nitrox and 1.5 positive when empty. Compared to 12L steels you'll need at least 5kg more for same exposure protection.

    3mm wetsuit (yuck) and steel plate and likely you won't need any additional weight.

  8. #8
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    I dived with Blue O Two using twinned Ali 80's last year - they came with a V-weight attached so didn't need to have a weight belt (was in a 3mm for the most part and Ali backplate). Only slight issue was that they only had two twins on board - for me and my buddy, and I found the valve was leaking from the left post on my check dive. So most the first few days were spent trying to fix it and they had no spares, which meant draining the tanks about three times before the problem was solved. Very helpful, they did everything possible to fix it - but they don't carry a back up and don't appear to test the ones they put on the boat properly!

    Had a great time, but if they'd not been able to fix it, we were a long way from anywhere with a supply of spare parts...

  9. #9
    anything but cool rivers's Avatar
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    It depends on exposure protection, wetsuit, drysuit, undersuit etc. I dived a set of twin ali 80s a couple of years back in Vanuatu. I didn't need any weight in a membrane drysuit with just a baselayer (in the UK, with a BZ400 and twin faber 12s, I need 4kg in the sea).

  10. #10
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    From what I've seen, it's pot luck if Blue O2 twins come with any purpose made weights. It's worth considering taking a couple of cam bands with you so if necessary you can attach weights to the cylinders and move them around to trim out.


 

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