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Ditching run time

Discussion in 'Hogarthian Diving' started by lefrogster, Feb 27, 2014.

  1. jadairiii

    jadairiii Solo Diver

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    First mistake, but we all make them when starting out in deeper diving

    Then you found an instructor that actually understood how to dive, problem solved. Good for you.
     
    Micksherryn likes this.
  2. Trace Malinowski

    Trace Malinowski Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Alexandria Bay, NY
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    "Chasing the run" is a bad idea since you want to make sure that you do all of your required decompression stops. Divers who chase the run sometimes cut short their stops to get back on time and on target. A complete understanding of decompression theory will allow you to plan a dive knowing what is theoretically happening at various phases. On the bottom phase you'll be on-gassing so you'll want to be able to call the dive and move off the bottom at the proper ascent rate as a team. Any delay and you'll continue to on gas adding to your deco time. Next, the deep stop phase attempts to control bubble formation and growth by adding staged stops between the bottom and the gas switch. For most technical divers these stops are 1 to 2 minutes in duration. Timing is important here because you want to continue up the water column without on-gassing until you reach the point at which you are theoretically off-gassing. You normally gas switch high enough above this point that you can choose to add time to your deeper gas switch to take advantage of the oxygen window effect. At this point you enter the intermediate stop phase. During deco here you want to complete all the planned stops. Delays are not a problem in the upper end of the mid-range and shallow stops because you are simply padding your deco with extra conservancy which would take you from nominal to +1, +2, +3, +4, +5, etc. Significant delays could change the game, but delays due to slow timing, delays in communication, pauses to deal with gear or teammate issues, and such are not a big deal after the gas switch. You may gas switch again in the shallow stop phase and you may want to adjust your shallow stops for conditions such as being cold by adding time. Upon surfacing, if conditions allow, it's a good idea to just rest and debrief the dive by floating on the surface or standing in chest deep water to keep some water pressure on the chest and take advantage of the surface deco stop. It's awesome when your team can move in trim and in unison. I like deco to be done on time and on target, but rather than worry about the run time, we worry about time through small sections. Like AJ said, the run is useful for letting you know how far off you are from where you should be. Gain a greater understanding of deco theory, Buhlmann, bubble models, inherent unsaturation, etc., and if you create your own ascent strategy be sure calculate your run time for the dive and even through the sections which denote the different phases and plan adequately for contingencies.
     
    GrimSleeper likes this.
  3. dvankirk

    dvankirk Barracuda

    # of Dives: 500 - 999
    Location: Cary, North Carolina, USA
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    I don't know how those PADI divers continue to live.

    It really isn't that hard to adjust your runtime on the fly if you need to.
     
  4. Diver0001

    Diver0001 Instructor, Scuba

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    I see a lot of minutes and counting in that, Trace.

    To my mind it's all a lot more straight forward.

    You basically have a few parameters to keep in you mind

    1) when are you still on-gassing?
    2) when does off gassing start?
    3) Pyle (deep) stop depths (roughly)
    and
    4) ceiling

    Granted I'm not a deep diving super-hero so this will break down at some point if you go deep enough and long enough but for Advanced Nitrox diving (which is mostly what I do) you can pretty much organize your deco on principles.

    The principles are pretty simple:

    1) if you know your PADI tables then you know what the NDL was at various depths. For most of the deco diving I do the 32% tables show you 95min @ 18 metres and 130min @ 15 meters. The air tables show 56 and 72 min at those same depths... I remember it as 55 and 70 to make memorizing easy.

    2) to me those depths define the "deep" and "shallow" parts of your dive. The deep part being depths where you are still on-gassing slow compartments and the depths where the NDL at that depth is less than (or equal to) your run-time up to that point. If you're deeper than the switch then you ascend @ 10/m per min. If you've reached the turning point you ascend @3m/min. (unless you ahve mandatory stops deeper than 15m, which I've never seen on nitrox).

    IN other words questions 1 and 2 above can be answered by looking at the tables. All you need to remember is 55 and 70 (or 95/130) and you know where your shallow part starts.

    3) Pyle stops have a certain calculation and deep stops have a certain magic calculation depending on your algorithm but in the context of AdvEANx you can pretty much flatten the issue into this: 1/2 max depth (2min)... 1/2 way from first deep stop to first required stop (2min) rinse and repeat. If you're smart enough to get into technical diving then you can count this on your fingers. (again this only applies to "baby" dives). That covers #3

    So far we can remember all of this (or write it down in a post-it note sized reminder on a slate).

    4) So the only thing left is the required stops. What do you do with those....

    ... yeah... you write them down. 18min@9m, 26min@6m etc.

    you can also make contingency plans for going over maximum time (or depth) and all of this can be written down on the back of a beer coaster.

    so for ADVEanX, all the deco schedules you'll ever need can be written down like this:

    32%; 18m/95; 15m/130
    21%; 18m/55; 15m/70

    12m @ XX min; +5 = yy-min; +10= zz-min
    9m @ XX min; +5 = yy-min; +10= zz-min
    6m@ XX min ; +5 = yy-min; +10= zz-min
    4.5m@ XX min ; +5 = yy-min; +10= zz-min

    don't bother writing down when you need to change gases because by the time you write you schedules like this you'll know when to change gases ... LOL

    Lost deco-gas schedules can be written down too but in the context of ADVEanX you can put yourself in the ball park by doubling the stop times after switches and as a last resort you can follow the computer and grind it out on back-gas.

    So... the nice thing about ADVEanX is that you have a lot of slop to work with and everything you ever needed to know about deco can be written down on the back of your hand :D

    Obviously when you're going much deeper or longer and juggling various mixes then the problem becomes much more involved that just remembering 4 numbers, 2 ascent rates and a hand full of stops. But I promised someone to write about this so I hope I'm not derailing the thread with it.

    R..
     
  5. GrimSleeper

    GrimSleeper Dive Shop

    # of Dives: 2,500 - 4,999
    Location: Ozstraya
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    What Trace said.

    When I did my training (which was DSAT, so kinda proto-PADI, I guess), and in all the trimix diving I did with some reasonably experienced folks in the Philippines for a few years afterwards, there was a broad acceptance that

    1. The last two or three minutes of bottom time was spent, as a team, prepping for the ascent - tidying up, stowing stuff, getting DSMB ready if you're going to shoot it on the run. That's the time for sorting out hoses, scooters, problems, etc - not halfway through an ascent.

    2. Deep, you keep to run time, as a slow ascent means you're on-gassing. Because you've prepped the ascent, there should be nothing to delay you anyway. Later in the ascent, and certainly after the switch to 50%, if you get held up you extend your run so that you complete your stop times. ie. if a three-minute stop at 21m takes four minutes, the rest of your run is + one minute.

    It's always seemed simple enough to me. Do people not do that anymore?


    Sent from my iPad using Tapatalk HD
     
  6. Trace Malinowski

    Trace Malinowski Cave Instructor

    # of Dives: 5,000 - ∞
    Location: Alexandria Bay, NY
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    Not really. It's pretty straightforward.

    Let's take a 200 foot dive for 25 minutes on 18/45 with Nitrox50 and 100% oxygen for deco as an example.

    If I use V-Planner the plan looks like this:
    Decompression model: VPM - B
    DIVE PLAN
    Surface interval = 1 day 0 hr 0 min.
    Elevation = 0ft
    Conservatism = + 2

    Dec to 200ft (4) Trimix 18/45 50ft/min descent.
    Level 200ft 21:00 (25) Trimix 18/45 1.24 ppO2, 76ft ead, 95ft end
    Asc to 130ft (27) Trimix 18/45 -30ft/min ascent.
    Stop at 130ft 0:40 (28) Trimix 18/45 0.87 ppO2, 43ft ead, 56ft end
    Stop at 120ft 1:00 (29) Trimix 18/45 0.82 ppO2, 38ft ead, 51ft end
    Stop at 110ft 1:00 (30) Trimix 18/45 0.76 ppO2, 33ft ead, 45ft end
    Stop at 100ft 1:00 (31) Trimix 18/45 0.71 ppO2, 29ft ead, 40ft end
    Stop at 90ft 2:00 (33) Trimix 18/45 0.66 ppO2, 24ft ead, 34ft end
    Stop at 80ft 2:00 (35) Trimix 18/45 0.60 ppO2, 19ft ead, 29ft end
    Stop at 70ft 2:00 (37) Nitrox 50 1.53 ppO2, 32ft ead
    Stop at 60ft 2:00 (39) Nitrox 50 1.38 ppO2, 26ft ead
    Stop at 50ft 3:00 (42) Nitrox 50 1.24 ppO2, 19ft ead
    Stop at 40ft 4:00 (46) Nitrox 50 1.09 ppO2, 13ft ead
    Stop at 30ft 5:00 (51) Nitrox 50 0.94 ppO2, 7ft ead
    Stop at 20ft 7:00 (58) Oxygen 1.59 ppO2, 0ft ead
    Stop at 10ft 12:00 (70) Oxygen 1.29 ppO2, 0ft ead
    Surface (70) Oxygen -30ft/min ascent.


    Off gassing starts at 151.8ft
    OTU's this dive: 89
    CNS Total: 38.5%
    141.1 cu ft Trimix 18/45
    22.2 cu ft Nitrox 50
    15.9 cu ft Oxygen
    179.3 cu ft TOTAL
    DIVE PLAN COMPLETE

    In my notes, understanding what is happening and how I want to amend my dive to take advantage of certain theories from phase to phase, looks like this:

    20 - 20
    30 - 4
    40 - 4
    50 - 4
    60 - 4
    70 - 4
    80 - 2
    90 - 2
    100 - 2
    110 - 1
    120 - 1
    130 - 1
    140 - 1
    150 - 1
    200 - 25


    For this strategy all I need to know is my baselines for ratio deco, at what depth I'm at 75% of max depth, 50% of max depth, my gas switches and do I want to use O2 effect, what I want to do about the 30 foot stop regarding a back gas break, and then from 20 up it's old hat.
     
    Last edited: May 16, 2014
  7. Ste Wart

    Ste Wart Master Instructor

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    Yes and No.

    Getting in the water with RD means you have a rough idea of how much deco you want to do. Once you get to 21m you still have the flexibility to decide how you want to do that deco. Are you going to split the time equally or are you going to lessen the time in the intermediate depths and add them to the shallows.

    You still need to move pretty sharpish at the end of the run time or you add to that deco, but if you don't just re-calculate at the 21m stop. You have a 2-3 minutes there after everyone has completed their gas switch, lots of time to work out your deco.
     

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