Hello and welcome to our community! Is this your first visit?
Register
Page 1 of 6 123 ... LastLast
Results 1 to 10 of 56
  1. #1
    TDF Member cprobertson1's Avatar
    Join Date
    Jul 2018
    Location
    Ayrshire. Scotland
    Posts
    87
    Likes (Given)
    38
    Likes (Received)
    36

    Gas planning with regards to pony cylinders

    Sorry guys, got a bit of a newbie question here: please don't slap me about too hard

    The ScotSAC lectures suggest planning for an additional third of your dive air requirements be added on as a reserve.

    For example, if I work out a descent/bottom/ascent/safety-stop will take 1000 litres of air, I should add +333 litres of air as a reserve - meaning I shouldn't go on this particular plan with less than 1333L of air.

    My question arises when we add a pony cylinder/bailout to the mix...

    Am I right in thinking that the reserved +33% of the required air should still be added into the main cylinder (and that the pony bottle's sole purpose in life is to get you safely to the surface with the required stops, and is sized accordingly to the depth you plan on having your accident)?

    My reasoning is that if you run into trouble - say, from entangelment, and use a lot of your reserved air freeing yourself - you then still have the pony to get you to the surface - whereas if your pony was the reserve, you've only got whatever is left in there. Is that reasoning correct, and as such, am I right in saying that in no way, shape, or form does a pony bottle increase your available bottom time?



    Many thanks - and sorry again... I feel like this is something I should just know, but it has only been touched upon in the lectures as "a pony is an independent air source" and assume you'll gain the rest of your knolwedge of gas management through your club and technical courses if you go down that route! Most of the other divers in my club use twinsets as well - so I've never even thought to ask until now!

  2. #2
    Established TDF Member Nickpicks's Avatar
    Join Date
    Dec 2012
    Location
    Dacorum
    Posts
    3,695
    Likes (Given)
    2736
    Likes (Received)
    1942
    Usually, a pony is excluded from gas planning. You plan the dive based on your main gas, and factor the reserve into that (often thirds, but other models are available), then the pony (or bailout if you call it that) is an emergency for the scenario of losing your buddy AND having a gas failure, or if you happen to get entangled just before the start of the ascent so eat into your reserve there.

    You are correct - the pony/bailout does not increase your bottom time. If that's how you're planning it, then you would call it a "stage" cylinder.
    The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at or repair.

  3. #3
    Established TDF Member
    Join Date
    Dec 2012
    Location
    NW UK
    Posts
    1,552
    Likes (Given)
    425
    Likes (Received)
    575
    Quote Originally Posted by Nickpicks View Post
    You are correct - the pony/bailout does not increase your bottom time. If that's how you're planning it, then you would call it a "stage" cylinder.
    And then you'd have lost gas calcs to do

  4. #4
    TDF Member
    Join Date
    Jan 2013
    Location
    Essex
    Posts
    203
    Likes (Given)
    22
    Likes (Received)
    22
    For me I would not include the pony/bailout in your calculations its to be used if you lose your main tank. As you state the 1/3 is added to your main cylinder.

  5. #5
    Established TDF Member Ron MacRae's Avatar
    Join Date
    Dec 2012
    Location
    Andover, Hampshire
    Posts
    1,453
    Likes (Given)
    1463
    Likes (Received)
    632
    You also need to check that your pony will get you to the surface if your main gas fails at the worst time, just as you are about to leave the bottom anyway at the end of a dive.
    You may be stressed and breathing like a train.
    If you get yourself off the bottom quickly, stay calm, and get to a depth where the gas lasts longer you may be OK.
    Make sure you do the maths for whatever depth you are at.
    Add in how long it takes for you to deploy a DSMB and get moving.
    A pony isn't a lot of gas, but it's better than trying to breath water.

  6. #6
    TDF Member
    Join Date
    Jan 2013
    Location
    Essex
    Posts
    203
    Likes (Given)
    22
    Likes (Received)
    22
    Quote Originally Posted by Ron MacRae View Post
    You also need to check that your pony will get you to the surface if your main gas fails at the worst time, just as you are about to leave the bottom anyway at the end of a dive.
    You may be stressed and breathing like a train.
    If you get yourself off the bottom quickly, stay calm, and get to a depth where the gas lasts longer you may be OK.
    Make sure you do the maths for whatever depth you are at.
    Add in how long it takes for you to deploy a DSMB and get moving.
    A pony isn't a lot of gas, but it's better than trying to breath water.
    Agree with this a lot of people think I got a pony I got lots of safety. 3l cylinder will last about 8.5 mins breathing normal at 30m, that's if its full. If your breathing a bit heavier say 50l/min that about 3 mins. For me, its get shallow quickly, then send up smb, then work out how long I can stay there.

  7. #7
    Established TDF Member witchieblackcat's Avatar
    Join Date
    Dec 2012
    Location
    Penwortham
    Posts
    1,800
    Likes (Given)
    1723
    Likes (Received)
    538
    I broadly agree with all of the previous comments. To clarify my thinking:

    1. A pony is only for use in an emergency and is not to extend a dive and nor is it included in gas calculations.

    2. A pony has a limited amount of gas so if you get an emergency deep or well into deco it may not have enough gas in it to get you out; you need to make sure that it contains enough so that if the emergency happens at the very worst moment your pony has enough gas.

    3. If you're in the situation where you're going deeper than a pony really has gas or you're racking up deco (actually of any real duration rather than just a bit too much for the pony) you probably ought to be thinking about other solutions.

    4. Just because you have a pony doesn't make you invincible. It's an extra safety measure not a get out of jail free card.

  8. #8
    TDF Member cprobertson1's Avatar
    Join Date
    Jul 2018
    Location
    Ayrshire. Scotland
    Posts
    87
    Likes (Given)
    38
    Likes (Received)
    36
    Quote Originally Posted by Nickpicks View Post
    Usually, a pony is excluded from gas planning. You plan the dive based on your main gas, and factor the reserve into that (often thirds, but other models are available), then the pony (or bailout if you call it that) is an emergency for the scenario of losing your buddy AND having a gas failure, or if you happen to get entangled just before the start of the ascent so eat into your reserve there.

    You are correct - the pony/bailout does not increase your bottom time. If that's how you're planning it, then you would call it a "stage" cylinder.
    Seems I was on the right track then! I'll add a note to keep it "invisible" to my gas planning (which puts it in the "not air I plan on breathing" category).

    Quote Originally Posted by Ron MacRae View Post
    You also need to check that your pony will get you to the surface if your main gas fails at the worst time, just as you are about to leave the bottom anyway at the end of a dive.
    You may be stressed and breathing like a train.
    If you get yourself off the bottom quickly, stay calm, and get to a depth where the gas lasts longer you may be OK.
    Make sure you do the maths for whatever depth you are at.
    Add in how long it takes for you to deploy a DSMB and get moving.
    A pony isn't a lot of gas, but it's better than trying to breath water.
    That is actually a good shout on the SMB - I've been calculating the required size based on faffing about for 3 minutes at 30m, and then beginning an ascent to a 5-minute stop at 3m (per murphy's law, making the assumption that my air supply gives out when I am the point of maximum ongassing during the dive and thus need to make a longer than average safety stop).

    I better add some faff-factor in there as well for the SMB. Next time I'm out (this weekend! ... I hope!) I'll time myself to see how long it takes to get the SMB up.

    My current guesstimate is that a 5L is probably best in my situation - while I can get away with a 3L, I'd rather err on the side of caution and assume that everything that can go wrong will go wrong (in the worst possible way, at the worst possible time). Last thing I want to do during an out-of-air incident is running out of air a second time!

    That may change in future - I'm just at the "planning" phase just now - figuring out the sort of money I need to save up! I also need to look at the formats that 5L comes in - because some of these literally look like 10L cylinders that are half as long, and that'd be really weird to carry. Maybe I could sling it? I also need to see if my BCD can float that much weight! ANYWAY - that's all a subject for another day!

    ... Another day when I am not totally skint!

  9. #9
    Established TDF Member witchieblackcat's Avatar
    Join Date
    Dec 2012
    Location
    Penwortham
    Posts
    1,800
    Likes (Given)
    1723
    Likes (Received)
    538
    Quote Originally Posted by cprobertson1 View Post
    That is actually a good shout on the SMB - I've been calculating the required size based on faffing about for 3 minutes at 30m, and then beginning an ascent to a 5-minute stop at 3m (per murphy's law, making the assumption that my air supply gives out when I am the point of maximum ongassing during the dive and thus need to make a longer than average safety stop).
    I think I'd consider the safety stop as unnecessary if I was breathing on a pony when I arrived at it.

  10. #10
    Last of the Mohicans gobfish1's Avatar
    Join Date
    Jan 2013
    Location
    the grassy knoll
    Posts
    3,782
    Likes (Given)
    4282
    Likes (Received)
    2365
    Don't bother with the faf
    Just get your arse back to 6m then faf with the bag as you do your safety stop two birds on stone.
    None diver as of 2018.


 
Page 1 of 6 123 ... LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •