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80 CF Aluminum as Pony Bottle?

Discussion in 'Solo Divers' started by 73diver, Dec 13, 2015.

  1. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
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    Another option is a 13 cf tank for travel. That's our solution.
     
  2. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
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    problem with 13's is they aren't really useful beyond 60ft for a safe ascent. If you have a 13cf bottle at 100ft it's going to be dry before you hit the top if you're ascending at the right rate and you sure won't have any chance of a safety stop on that thing. Not to bash your decision or anything, but make sure you're doing the actual calculations to see how long that thing is actually going to last you before you rely on it.

    80's are fine as pony's, we carry them as stages all the time. Little overkill, but if you're going to that effort, it's easier to just dive sidemount with a pair of 80's for the pretty fish diving and call it good.
     
    Dhboner likes this.
  3. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
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    tbone1004. There are so many threads on the relative merits of various size ponies that a quick search will give the OP more then he probably wants to read. Each individual has to assess their individual needs, available options, diving conditions, abilities and individual risk/benefit philosophy.

    Individual mileage may vary...

    Depth 99 feet = 4 atm. Sac .7 "average." And rounding up.
    1 minute to switch over = 3 cf
    2 min to ascend to 15 feet = 3.5 cf
    3 minute SS = 3 cf

    Total = 9.5 cf

    Any dive less then 40 to 60 feet I might not even bother with a pony.

    The down side of a 13 cf pony is that a small loss of gas can be significant and most divers will need to keep it full to get the max benefit. There is also the consideration of vip and fills at arrival verses whipping.

    A third option is to check for a tech shop at your destination. These will almost always have 19, 30 or 40's to rent.

    And of course you can always just rent the 80's but always good to know all your options.
     
    Last edited: Dec 14, 2015
  4. Roman_66

    Roman_66 DIR Practitioner

    # of Dives: 200 - 499
    Location: Allen, TX, USA
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    0.7 it is a good air consumption for good diver with good physical condition (which is not me :)).
    Even that, for stress situation (and OOG for sure is one of the stressful situation for any diver) you should calculate air consumption at least as 1.6 from regular.
    Ascend from 100 ft to 15ft (100-15=85) should take about 3 mins. I know safe ascent rule: 9 meters = 29 ft per 1 min
    Additional to that, it is pretty difficult to breath till real zero in the tank + you need to keep about 10Bar = 150 PSI for gauge correction.
    IMHO :
    1. 13cf can be ok for emergency ascent from 100ft without safety stop in case diver well trained and not panic
    2. 19cf good for ascent from 100ft with safety stop 15 ft for any diver
    3. 30cf good ascent from 100ft with all DIR safety stops (50,40,30,20,10 ft) + enough time to find and inform your buddy about the incident.
     
  5. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
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    Hi Roman and thanks for your input. But keep in mind that this is the solo diving forum and as such

    1) the diver should be experienced and able to handle stress without panic.

    2) know how to safely ascend as quickly as possible. How they choose to do this will vary from diver to diver and dive to dive

    3) no need to search for buddy
     
  6. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

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    switch, fine
    ascent is way too fast. should take twice that time.
    3 min ss is cutting it somewhat close after a rapid ascent from 100ft, so my math says
    3+7+5=15 if you using .7 average, but considering that is most peoples normal sac rates, and that first minute it will likely double, you're up at 18cf used and even with a 19 there is 0 margin for safety and you better hope you had a full tank. Other issue is 13's and 19's serve no real other purpose in diving, so at least if you go with a 30 it's useful if you get into deco diving. It's only 5lbs heavier than a 13 as well
     
  7. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

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    I've used 6s and 13s as dry suit inflator bottles on cold water trimix dives, but even as a pony, a 13 is enough for a 30 fpm ascent and safety stop from 100' even with a 1 cfm per minute SAC.

    The ascent itself will take 6.6 cu ft.

    A 3 minute safety stop at 15' will add 4.4 cu ft for a total of 11 cu ft.

    However, if you make the safety stop at 10' instead, you'll use 6.5 cu ft for 5 minute safety stop, sucking the bottle dry, but getting you nearly the full 5 minutes even if you actually breathe 1 cfm, while at rest for those 5 minutes.

    In the real world, you'll use less unless you are a real hoover and doing the full 5 minutes with an ascent to the surface on just a 13 is do-able.

    A 19 offers about 5 cu ft of reserve for that same 100' ascent and 5 minute safety stop, and that 19 cu ft tank is the same diameter, only 6" longer and is about a half pound less negative in the water, so it's pretty much a "win" all the way around.

    Of course, a 30 cu ft tank is only 1/2" larger in diameter, 3" longer and another 1/4 pound less negative in the water than a 19. Plus, at 30 cu ft, it's large enough to make a useful O2 bottle if you get into technical diving. Which is why I've never owned a 19 - anything it can do, a 30 can do better with about the same feel in the water.

    My 13s are now doing double duty as CCR O2 bottles.
     
  8. uncfnp

    uncfnp Solo Diver

    # of Dives: 500 - 999
    Location: North Carolina
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    Remember guys, we are talking about a tank for travel. In this case that marginal extra size and weight does matter. It might not be optimal but it is doable.

    tbone. As I said, every diver is different and a 13 does need to stay full. I have 13's, 19's and a 30. I travel with a 13. My sac rate drift diving is .35 to .4. With current it goes up to .5 My partner also travels with a 13 but uses a 19 at home. His sac on a good day is .7
     
  9. Bison Ravi

    Bison Ravi Solo Diver

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    If it were me, instead of traveling with a tank, I'd just sidemount 2 al80. More confortable than a backmounted tank plus any pony, more streamlined and you have lots of air. Also your harness/wing will be a fraction of the size and weight of any jacket bcd or harness/backplate.
     
    tbone1004 likes this.
  10. scuba127

    scuba127 Barracuda

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    Yep....side mount...I solo dive Bonaire using side mounted aluminum 80's....prior to that I used a back mounted 80 with pony slung....would never go back to this configuration for solo diving after training to side mount...
     

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