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SPG & Twinsets

Discussion in 'Technical Diving' started by Ian, Nov 16, 2010.

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What SPGs do you have on your twins?

  1. None

    0 vote(s)
    0.0%
  2. Single SPG on PRIMARY regulator

    33.3%
  3. Single SPG on SECONDARY regulator

    33.3%
  4. SPG on BOTH regulators

    33.3%
  1. Ian

    Ian New Member

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    I'm thinking of switching to my own twinset after doing a couple of TDI courses in twins overseas. What is your take on SPGs?

    PS Thanks Jenkins - yes, I'm thinking about MANIFOLDED TWINSET
     
  2. Jenkins

    Jenkins Friends, Romans, countrymen, lend me your ears.

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    I have assumed you are thinking of a manifolded twinset - if diving indies I would want a SPG on each cylinder.
     
  3. Roy

    Roy Active Member

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    Just one if manifolded.
     
  4. bottlefish

    bottlefish Super dooper member
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    Just the one, on the secondary (left post)

    Two adds an unnecessary point of failure..... whilst SPG and HP hose failure is not exactly common, it's still not unheard of, so why would you want to double your chances of having one, when a single SPG will tell you how much gas you have left.

    Bear in mind that the SPG is not there to tell you when your gas is going to run out, it's there to provide you with information on when you should turn the dive, based on how much gas you've used, to ensure that you don't run out of gas. If you have a situation where you have to shut the manifold, and loose access to that SPG, then you've already turned the dive, that decision is no longer relevant. You either have enough gas to ascend or you don't.... (although giving your team members a hug on the way up may not be a bad idea ;))
     
  5. Major Clanger

    Major Clanger P-Plated Meg Diver

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    Not being funny mate but you're asking some pretty basic questions. Nothing wrong in that but does raise a few alarms. How much do you know about what you'd like to get in to and why you want to do it? Have you considered an intro to twinset course. TDI one is only a day and well worth it. Having said that, I see you've done the TDI ANDC courses. What was your equip config then, didn't they cover equipment setup or do dives on twins.
     
  6. Ian

    Ian New Member

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    Major Clanger - thanks for your comments!


    My reason for switching from my current 15+pony to twins is that I'm doing longer and deeper dives with more deco to see the wrecks I want to see. So I need more gas and more redundancy, and a rig that is suited to carrying stages for accelerated deco.

    On the TDI courses, I was taught to use a dual bladder wing and a single SPG - for all the reasons discussed in this thread and my other related one. I talked with the guy teaching me about these issues and he gave the same reasoning as you guys. I did 7 dives on twins, and we discussed setup a lot, although with a slant toward warm water diving. To redress that bias I plan on doing my entry level trimix in the UK - but I need to buy kit and get used to it first...

    The reason I'm asking here is that I dive with quite a number of (experienced and well respected) divers in the UK who use twinsets, who have 2 SPGs and single bladder wings. I just wanted to see if there was something I was missing about the benefits of this setup that was perhaps applicable to cold water diving in a way that I (and my instructor) hadn't fully considered.

    Having had a number of less than satisfying training experiences over the years (with a variety of agencies) I'm afraid I never take any one instructors word as absolute gospel - I like to make sure I fully understand ALL the arguments before I decide how I will proceed (especially when committing £££). That will include asking some of my friends with two guages why they chose that config too!

    The wisdom of this group (especially on guages) seems pretty unanimous however!

    Thanks to all!

    Ian
     
  7. Major Clanger

    Major Clanger P-Plated Meg Diver

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    All is clear. Good luck with trimix. Mine to 60m is in March at NDAC and likely to be a bit cold.
     
  8. Badger

    Badger Member

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    That is well put. I would add to that if you had shut down your right post you really want go to your team mates gas for the ascent (that's what you plan for right?) and bin the rest of you back gas. Continuing to breathe yours may be OK but the added stress of waiting for it to breathe down (or not) may just compound a stressful situation.
    That's why getting an OOG ascent drill 100% comfortable (possibly including SMB launch and stops) is so important. Its also why proper gas planning, not just 'thirds', is also vital.
    Hugging is also good but a second SPG does not help with any of this.
     
  9. Bobco

    Bobco Active Member

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    Spg off left post on secondary system all as above. Welcome to twins Ian
     
  10. bottlefish

    bottlefish Super dooper member
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    Did you mean left post (right post shutdown, your SPG is still functional....)? Not sure that I'd bother with the binning bit though, I've got some gas, may as well use it, I'd just stick closer then normal to the team, and look forward to my first gas switch.

    Gas doesn't just run out, you get some warning, the breath will stiffen up a bit first... first sign of that, I'll be looking for a donor
     
  11. Badger

    Badger Member

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    Sorry, typo I did mean left post. From the perspective of my training I would know that my back is completely 'disposable' so the shut down is a matter of housekeeping. It may well be that fault is fixable, if so happy day. If not then my team mate is right in front of me anyway (possibly assisting with the diagnostics) so I would signal for the long hose and bug out/up rather than wait for my back gas to go and add another potential stress point to the situation (Murphy's law says it will go just when you don't want it to!)
     
  12. bottlefish

    bottlefish Super dooper member
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    Thought it may be ;)

    Different training, different perspectives on things Thumbs Up
     
  13. Badger

    Badger Member

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    Sure, agree, its one of those 'details' that make less sense out of the larger context (although I would stand by it as a better strategy than isolating and finishing your own gas:D)

    For example it gives a continuity with cave training. With exit speed being paramount, having to halt the team, donate, reorder the team and then continue to move a second time is just a faff. It also means that if you hit a viz problem on exit you are not doing so knowing your gas might go and have to go to a OOG with limited visual reference.
     
  14. bottlefish

    bottlefish Super dooper member
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    Long as you're happy with your decision ;)
     
  15. Elvis

    Elvis Banned

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    I think this was raised on t'other place the consensus was that there is little point having both (due to additional failure points) but if you have one put it on your secondary, as there was a chap who had it on his Primary, the isolator was closed and he didn't realise because the SPG was still falling.
     
  16. BlueLabelDiving

    BlueLabelDiving New Member

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    I agree. Having only one SPG is a lesser failure point. It is also a check that your manifold is opened and in case of an unidentifiable gas loss, easy to detect once isolated. In case of free-flow shut down, this happens most of the time on the reg you're breathing from, meaning your right post, hence you're still capable of assessing your losses after a primary post shut down...
    Redundant wings... I only use them when overweight on large steel twins, where a drysuit(or wetsuit) can't comfortably bring you to the surface. Diving for more than 10 years on twin bladders, I never had a primary inflator fail, but I had the back up inflator auto-inflate. hence it became more of a liability than a back up. I swapped to a lighter, single bladder wing and carry a lift bag with a top purge valve in case of catastrophic buoyancy loss. Practice is needed though. I find hugging the lift bag while it is attached with a quick-release to your scooter ring the most controllable.

    Ben
     

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