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Petrel 20ft safety stop?

Discussion in 'Shearwater Research' started by Julian55, Jan 5, 2013.

  1. Julian55

    Julian55 Barracuda

    # of Dives: 200 - 499
    Location: New Westminster,BC
    298
    8
    18
    So I will be using my computer as OC for Nitrox, does the Petrel have a built in 3 min safety stop at 20ft? If not can I set it up that way?
     
  2. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    11,518
    1,702
    113
    You have a superb computer, but you are in effect asking how you can ignore some of it's best features and just run it like a cheap hockey puck computer. That's a real waste.

    Generally speaking Shearwater computers leave you in charge of the decisions and give you a wealth of information to make well informed decisions about ascents and safety stops. Consistent with that, if you want a 3 minute safety stop, you can just add 3 minutes to the run time after you reach 20'. However if you do a little homework you'll find you can use the computer to give you great information and use a couple options to determine your safety stop length and control the ascent.

    You have a great deal of control over conservatism and the 'curve' the computer uses to calculate NDLs and stops, so you may decide to change from the default 30/85 gradient factors and add conservatism by lowering the high gradient factor - to 30/70 for example. In effect, this advises a stop when the gradient in the controlling compartment reaches 70% rather than 80%. Along with or instead of this, you may opt to read the actual gradient as you ascend and you'll note the gradient will increase rapidly as you shallow your depth, and then decrease over time as you hold at a depth. It's enlightening to see what the gradient does on the "safety" stop then on the ascent and it won't take you long to figure out when a shorter or longer safety stop may make sense (and that's a while lot more useful than an arbitrary 3 minute or 5 minute stop). Watching the gradient you'll also see the benefit of a slow ascent from the stop depth, versus just popping up at 30 fpm.
     
    Caissy likes this.
  3. bamafan

    bamafan Manta Ray

    # of Dives: 200 - 499
    Location: Panama City Beach, Fl.
    984
    469
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    As stated above just change the gradient factors. You can use the planning function to see what the added time would be. 30/70 is very conservative. When I dive my Petrel or Predator and bring along an old Oceanic hockey puck computer the Shearwaters go into deco several minutes before the Oceanic. Now once deco starts on the Oceanic it gets stupid. I will have 30-40 minutes deco on the Shearwaters and 1 1/2 to 2 hours on the Oceanic. If you are not putting the Sheawater in deco just stop at 15 - 20' for 3 minutes if that is what you want.
     
  4. Ken T

    Ken T Solo Diver

    # of Dives: 50 - 99
    Location: Calgary, AB, Canada
    265
    66
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    I received a petrel recently.

    I too will be diving OC within recreational limits...at least for a few years until I feel confident enough to start some introductory tech courses.

    I have been reading up on gradient factors : Gradient Factors, Matti Anttila; Clearing up the Confusion about Deep Stops, Erik Baker; Understanding M-values, Erik Baker are available online from various sources.

    The tissue graph demonstration video by Shearwater is also excellent.

    I have not played with the onboard dive planner a lot yet, but it should be instructive I imagine.

    Cheers!
     
  5. graham_s

    graham_s ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Al Khobar, Ash Sharqiyah, Saudi Arabia, Saudi Arab
    187
    61
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    Why not just stop at 20ft and wait for 3 mins?
    Do you need a computer to tell you, when you know that you should?
     
  6. KWS

    KWS ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: SE TEXAS
    4,817
    1,214
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    You guys got me thinking ... i have the preditor. i thought it had the 3 min stop in it. also a setting for the min depth for stops in general. i have mine set at 20 ft. now i have to go home and look. try the planning mode, it is very easy adn see what it says.
     
  7. 616fun

    616fun Divemaster

    # of Dives: 200 - 499
    Location: Indianapolis, IN
    848
    122
    43
    These recent questions on the Petrel have me wondering why purely recreational divers are buying them. It's way more computer than is needed for that level. If you are looking for the OLED display and the conservatism then why not buy the Atomic Cobalt?
     
  8. divad

    divad Solo Diver

    8,113
    2,176
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    ---------- Post added January 6th, 2013 at 10:38 AM ----------



    You can set yourself up that way.
     
    Last edited: Jan 6, 2013
  9. Wayne at DiveSeekers

    Wayne at DiveSeekers Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: New Jersey
    863
    170
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    We have found that the main reasons our people are going with the Petrel over Cobalt is because it is a wrist computer and they don't need air integration.
     
    James R likes this.
  10. Jim Lapenta

    Jim Lapenta Dive Shop

    # of Dives: 500 - 999
    Location: Canonsburg, Pa
    16,947
    8,761
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    Agree with Wayne. I wanted a wrist computer that had all the options for rec and tech including up to trimix but didn't have air integration, or silly stuff like a heart monitor. The Petrel is on my wishlist to compliment my Predator. Unless all these guys buying Petrels decide to sell their Predators. Then I have no problem getting another one of them if the price is right. I also like the amount of control I have and that Shearwater treats me like an adult when it comes to planning and executing dives.

    "It's way more computer than is needed for that level."

    As for this statement so are most of the computers out there. For recreational dives a computer is really not needed at all. A simple bottom timer and tables will work. Yet we have vacation divers sporting Luna's, Sol's, ProPlus 2's, Cobalts, D9's, D6's, D4's, Icon's, etc.. All of these are way more than needed. To me these are more of a waste of money for purely recreational divers.
     

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