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Wot I lerned on my last dive trip

Discussion in 'General Scuba Diving' started by Wibble, Dec 31, 2017.

  1. Wibble

    Wibble Fish don't talk
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    The great thing about diving is learning something new, even if it is pretty obvious to some it's always new to someone else or useful as "revision" to others.

    Specifically, we learn a lot from mistakes or doing things outside of our comfort zone. Do share your stories...
     
  2. nickb

    nickb Active Member

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    Make sure you turn your gas on before entering the water if you wish to see your loved ones ever again, particularly if you're fool enough to dive with a semi-closed rebreather.

    This did NOT happen to me.
     
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  3. Wibble

    Wibble Fish don't talk
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    Don't use steel tins for stages...

    Bleeding obvious really, but was good to try it out. I thought that for a bottom stage (a stage cylinder which would be used for extending the bottom portion of a dive, you switch to back-gas when it's depleted) if an aluminium cylinder was used it would get extremely floaty and therefore tip upwards and be a complete embuggerance.

    It's possible to take a technique from the sidemounters and clip it on a forward belt D-ring, thus dragging it down.

    It's also possible to clip the stage under another (full) stage and keep it under control -- the right answer.

    But no, I thought I'd try a steel stage as this would be slightly heavy when empty, so not float upwards. The maffs means that it's circa neutral when empty - Subaqua.co.uk diving calculator
    So, on paper, seems like a reasonable idea.

    I've a couple of candidate bottom stages to play with, AKA sidemount cylinders. So, wearing my 'standard' twinset, I attached one of those steel cylinders along with two Aluminium 80 stages containing deco gasses -- two left, one right. Then jumped into Vobster with a couple of buddies.

    Feck moi.

    Aside from being grossly overweighted -- wing filled to bursting point and my suit pretty full too -- I managed to stop sinking. But that was only part of the problem; I had to almost go into a 'banana' shape to keep from turning sideways with the weight!

    Stuff that for a game of soldiers. After a minute of that 'trim hell' I decided to ditch the thing and pick it up later. So took it off and put it down whilst dumping a lot of gas from my wing to compensate.

    One of my buddies then decided he'd carry it. Bad move! Same problem, so he ditched it 30 seconds later, but on the APC / tank thing. NP, just mark it with an SMB. Wasn't my best launch of an SMB as the spool left my hand. Good design feature of the shiny Apeks spools is they do slowly descend, so I caught it on the way back down and clipped it to the stage.

    And we continued our bimble and picked up the stage at the end.

    Lessons well and truly learned. Firstly, steel cylinder/stages are great for Sidemount where there's two to balance each other, but are a complete CF when you use one. Secondly, what works in theory doesn't always work in practice! Thirdly, playing aroung / experimenting like this is exactly the point of the relative safety of the quarries.


    ...
    When I went to pay at the end of the day, the guy in the shop said that they'd seen the SMB on the surface and took the boat over to pull on the SMB to see if there was anyone attached and realised it was tied off. Didn't think of that; was just using the SMB for marking the stage to collect it later. Nice to know that they're looking out for us.
     
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  4. timmyg

    timmyg Super Moderator
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    How the purest has changed......

    I’ll admit, that’s something I don’t get, L&R. I went from LL RR to all left, and for 3 prefer all left, or 2 left & one behind & rotate as required.

    That said, SWMBO does 2:1 on the rare occasions she has 3 stages.

    But as with everything diving, each to their own.

    TG

    Sent from my iPhone using timmytalk
     
  5. Tel

    Tel Super Moderator
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    Would have thought the first thing to learn would be to do a standard buoyancy check in the confined area first :p
     
  6. Wibble

    Wibble Fish don't talk
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    Purist? Was something I meant to expand on...

    Using both sides is something which Mark P mentioned when doing the Normoxic Trimix course. It's also popular with (some) rebreather divers diving with two stages.

    Am very happy with two left but the first attempt at putting an ali 80 (third stage) on a leash was bloody awful as the thing dangles between one's legs and is sodding uncomfortable. As ever, it's always easiest to get someone to show you how it's done, but I don't know anyone who dives with a leash. So I've been messing around with putting a stage to the right to see what it's like.

    Being careful when clipping the stage on is important; don't want to trap the longhose. A donate is pretty straightforward; get the reg from the mouth into the donee, then release it from under the cannister which may mean reaching under the stage or even unclipping it. But everyone lives.

    The biggest challenge is where to park the torch when doing a stage switch, particularly when switching from Lean-Left (e.g. 50%) to Rich-Right (e.g. 80%). I found that parking the torch on the left-hand D-ring was easiest as you go through the OxTox protocol for the RH stage.

    Anyway, it's fun to experiment and any new 'knowledge' or experience is good even if it's to realise that it's all wrong. And it's something to do in the winter season to relieve the boredom of a quarry.


    @Tel - how does one do a buoyancy check with three stages and a twinset? As all of them were full of O2+N2, so that's ~15kg of gas in those tins! Hmm. a 40lb wing is 18kg.
     
  7. Tel

    Tel Super Moderator
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    You said yourself that you were overweighted and the wing + drysuit struggled.
    I thought diving 101 was to make sure all was ok before jumping in, so oh dunno maybe the confined area would
    have allowed you to check whatever rig you've decided on this month could cope and your trim was at least passable.
     
  8. Wibble

    Wibble Fish don't talk
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    :)

    I went in in my "normal" rig with normal weighting with the exception of the steel stage which I knew would be 4kg more or thereabouts. Was somewhat surprised at what that means in terms of pumping gas into the wing and keeping a lateral trim. I didn't touch the bottom though, except for putting the steel stage down.

    Kind of was a weight / trim check really, just not in the confined bit. Definitely would be a bad idea to do that on the south end of the NDAC pontoon though!

    It does show (to me anyway) how hard it would be to do an accurate weight check in full technical kit with multiple cylinders, batteries, and preparing for long deco times in cold water, i.e. where you don't want suit squeeze at the 6m stop and *especally* where you're donating gas, etc.

    Actually I'll take that back; just jump in with empty cylinders and stages and keep a 6 metre stop.
     
  9. jb2cool

    jb2cool Moderator
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    I think a 40lb wing is good for 2 stages (Ali), more than that and you need a bigger wing. This is ‘common’ knowledge and is part of the standard rig.

    I didn’t realise how bad it would be though so glad you experienced it rather than me.
     
  10. Wibble

    Wibble Fish don't talk
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    If only I dived with people with "common" knowledge... :)

    Two ali80s on my 40lb Halcyon Evolve work fine. TBH three ali80s is OK too. Definitely not the steel though!

    What's the next 'standard' wing size up that's common on T2 dives?
     
  11. jb2cool

    jb2cool Moderator
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    60lb is the next boy up i think
     

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