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Diving to 200' and Beyond

Discussion in 'Advanced Scuba Discussions' started by Flutter, Feb 6, 2016.

  1. giffenk

    giffenk Great White

    # of Dives: 500 - 999
    Location: toronto
  2. ajduplessis

    ajduplessis Solo Diver

    # of Dives: I'm a Fish!
    Location: dry land :-(
    Not family of Doc Deep by any chance?
    jacobf123 and The Chairman like this.
  3. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
    Location: South Santa Monica Bay/Los Angeles California, USA
    She must have a phenomenal Surface Consumption Rate (SCR) of around 7 to 11 liters/min per ATA. That's about 0.6 to 1 bar/min per ATA pressure SCR. Let's use 1 bar/min per ATA for the 11L/bar AL80 Tank.

    It's an obvious multi-level dive starting deep at 60m (7 ATA); Depth Consumption Rate (DCR ) is 7 bar/min, if she stays 5 min, then she consumes 35 bar starting from full fill of 200 bar (165 bar remaining).

    She ascends to 30m at 9m/min consuming 20 bar (145 bar remaining), and stays 10 min at 30m (4 ATA) using up 40 bar (105 bar remaining).

    Then ascends to 15m at 9m/min consuming 7 bar (98 bar remaining or half tank), and stays 20 min at 15m (2.5 ATA) using up 50 bar (48 bar remaining).

    Finally ascends to 12m (46 bar remaining), and stays 10 min at 2.2 ATA using up 22 bar (24 bar remaining).

    Lastly ascends to 6m (22 bar remaining), for 5 min safety stop at 1.6 ATA using up 8 bar (14 bar remaining in AL80 tank and essentially empty). Switches to Pony bottle as needed for ascent to surface.

    Total run time 50 min for this solo multi-level "NDL" dive profile starting at 60m/200'.

    Now a big caveat for a buddy team going to 60m/200' :

    Dangerous Allure of the Single Tank Deep Air Bounce Dive
    A 60 meter bounce dive on a single AL80/11litre per bar cylinder, you will need well over half a tank (130bar out of a full tank of 200bar) just to get both you & a buddy to the surface in an emergency air sharing contingency --and that's assuming an "under control" max recommended ascent rate of 18m/min, a "non-stressed & nominal" breathing rate of 2 bar/min per ATA for both divers, and also most likely performing a deco/"safety" stop of several minutes with whatever air remains (a very narrow & non-robust set of assumption parameters to meet for recovery from this contingency, given the single tank).

    So after reserving 130bar for the contingency above, that leaves you 70bar of gas usable for the dive. Assume you use 20bar of this usable gas on the fast descent to level off at 60m (initial exertion entering the water, inflating the BCD for neutral buoyancy at depth etc) --so you actually have 50bar usable at 60m.

    At 60m (7ATA), your gas consumption rate will increase sevenfold from 2bar/min to 14bar/minute, so with only 50bar usable from above, you've got a maximum of three minutes at this depth. In short conclusion, this bounce dive is "do-able" on a single AL80, provided you can handle the extreme narcosis. . .

    Last edited: Feb 7, 2016
    fsardone likes this.
  4. fsardone

    fsardone Solo Diver ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: Rome, Italy
    Couple of points.
    I do dive deep and/or solo. When I go deep usually is for wrecks, there often life is abundant and light not always scarce.
    The following video was on a GoPro 3 Black during a dive to 60m/200' (you can see the computer in a couple of freeze frames, I am the diver).
    You will notice the huge ambient light (this is south Sardinia) but bright colors only pop up when hit by dive lights.

    Here I tend to agree. Lets make a few calculations.
    Let's say we have only one 80 cf tank (pardon me but I deal metric) which is about 2200 liters (I know because I use 80s as stages or bailout in CCR). In deco (no activity) I burn 14 liters/minute in tech config, she is great and uses less than I do in deco let's say 10l/min and she dives to 60 meters 7 bar, which means she using 70 liters per minute in bottom fase, she does 1 hour dive and uses air.
    This allows maximum 13 minutes of bottom time (3 descend and 10 stay at 60 meters) and abut 43 minutes deco using 1900 liters of gas. Feasible but 0 reserves, especially if considering an extended bottom time for any reason, distraction, entaglement. 15 minutes bottom (3 descent 12 stay @ 60 meters/200') is all the air she has and I am not considering BCD and (possibly) dry suit inflation.
    In all of this I am not considering the pony which is her escape. Lets say she loses her gas at the most critical point (end of bottom phase). She would have used
    12min * 10 liters/min * 7bar = 840 (bottom phase)
    3 min * 10 liters/min * 3.5 bar (average dept) = 105 liters
    Foe deco, she needs 2125 (gas consumption calculated by deco sw)-945 about 1182 liters.
    If she has an s40 she barely has the gas to come out alive and not bent.
    Keept in mind that anything goes wrong and your ventilation rate skyrockets.

    If we calculate anything beyond 60m/200' this becomes just bollocks.


    lamarpaulski, Flutter and Kevrumbo like this.
  5. fsardone

    fsardone Solo Diver ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: Rome, Italy
    Kevrumbo just beat me in posting while I was typing, we came to pretty much same conclusion doable (with or without buddy) but risky ... no margin for error.
    Kevrumbo likes this.
  6. WarrenZ

    WarrenZ Solo Diver

    # of Dives: 200 - 499
    Location: Las Cruces NM
    They dont make them like that any more. Ill bet she has seen some things in her career.
    oldschoolto likes this.
  7. Patoux01

    Patoux01 Solo Diver

    # of Dives: 100 - 199
    Location: Geneva
    What's the internal volume of a 83 tank? It's not uncommon for the frenchies (and the swiss actually) to dive to 60m on a 12 or 15l...

    As for the 80' CESA... the CMAS ** instructors in France are supposed to come up from 100' on CESA. (it only got removed last year, and is still being discussed currently)

    Stupid? Yeah, obviously.
  8. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    The "problem" is that usually you don't need the margins. They're only required when things go pear-shaped, and fortunately that doesn't happen very often.

    How many thousand kilometers have you driven your car and never needed your seat belt? Does that mean that it isn't prudent to wear one?
    LowVizWiz and fsardone like this.
  9. Kevrumbo

    Kevrumbo Banned

    # of Dives: 1,000 - 2,499
    Location: South Santa Monica Bay/Los Angeles California, USA
    (And when it all goes pear-shaped):

    The infamous & creepy tragedy of Yuri Lipsky who recorded his own demise:

    There but for the grace of God (go I). . .

    The Cozumel 90m Bounce Dive Tragedy:

    cozumel accident 9/4/11, THE FACTS
    Last edited: Feb 7, 2016
  10. Mr.X

    Mr.X ScubaBoard Supporter ScubaBoard Supporter

    What's interesting is bit with age + assumed "diving wisdom." Old and stupid = young and stupid too.
    What's good is that she's doing it alone, but as mentioned in a previous post she'll ruin someone's day at some point. The good bit is perhaps she's doing what she likes irregardless. The minute someone starts demeaning other profiles as "baby" or other - clear sign to stay away.

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