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Thread: SCR Dive planning?

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    RBW Member EdwardHall is an unknown quantity at this point EdwardHall's Avatar
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    SCR Dive planning?

    Hello,

    I have V-planner, and have used SCR mode but am trying to plan for a Hollis Explorer.

    I have a Prism 2, and that's easy to plan for, but this explorer is frustrating with it's DCP, and never knowing what PO2 to plan for.

    We set a Nitek Q for the 38% mix in the tank, and the NDL time seemed to come out the same.

    I have also been told to lower the NX in the tank by about 4 percent as it will be lower in the loop which makes sense.

    I have also heard guys that state they have gotten 90 minutes time at 100 feet. They have to have some Deco at that point, it's a non deco unit.

    How do you guys with Explorers or other units plan your dives?

    It sure seems convoluted to me.

    I am trying to see the differences at 100 feet between her sidemount SMS50 rig using 2 x AL80's, and 1 AL40 50%, and her using her Hollis Explorer.

    I know the explorer is a little different, but is it THAT much different from how other SCR divers live?

    Maybe some of your dive profiles around 100 or so would help. What do you plan for?

    I have attached a spreadsheet with her dive log. While it jumps all over like a box of frogs it seems to stabilize at 1.32 or so at 100 ft.

    Thanks

    Ed.
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    Last edited by EdwardHall; 29th March 2014 at 02:19.

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    RBW Member skip is an unknown quantity at this point skip's Avatar
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    Re: SCR Dive planning?

    The dragger dolphin is a bit different from the Hollis Exp. In the dolphin we use orifices that correspond to mix. For example the 60% orifice for shallow dives, and a 50, 40, 32% orifice. For 100 foot dives, the 32% orifice is appropriate. And that is the mix in the tank. The breathing loop won't be 32% but will be less depending on workload. There is a formula for determining the mix in the loop, but a look-up table is provided.

    At medium workload (1.25 lpm, .044cf/m) the mix in the loop is 26%. The computer is thus set for 26%. I program in 28% and 24% too. In the event that I work more or less and my O2 monitor shows something closer to one of these I can switch over during the dive.

    By the way, the continuous flow of the dolphin means that I can get 51 minutes of dive time at 100 feet (flow rate is 15.5 ppm) and I'm using 30cf tank of 32%.

    ignoring rule of thirds in gas management, and keeping the plan to 45 minutes, Vplanner says that with 100% O2 for deco, I'll have 15 minutes of Deco. first stop at 30 feet on back gas, for 4 minutes, so 11 minutes on the O2.

    By the way.... I could increase bottom time by carrying a bigger tank. 96 minutes on a 40cf tank, and 129 minutes on a 70 cf tank. I sometimes dive a 63cf tank that I rigged for the dolphin.


    skip
    Last edited by skip; 30th March 2014 at 14:31. Reason: add by the way.

  3. #3
    RBW Member EdwardHall is an unknown quantity at this point EdwardHall's Avatar
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    Re: SCR Dive planning?

    Interesting Skip. So you leave your computer in Open Circuit mode for this type of planning?

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    RBW Member LLWS will become famous soon enough LLWS will become famous soon enough LLWS will become famous soon enough LLWS's Avatar
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    SCR Dive planning?

    Explorer Dive Plan: Swim until it tells you to stop swimming. As far as a legit dive plan, it's basically too much trouble due to the number of variables. I use to argue you could easily plan against OC on air, but then we caught the Explorer allowing <air equivalent PO2 depending on DCP so that doesn't work either.

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    RBW Member skip is an unknown quantity at this point skip's Avatar
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    Re: SCR Dive planning?

    Quote Originally Posted by EdwardHall  View Original Post
    Interesting Skip. So you leave your computer in Open Circuit mode for this type of planning?
    yes, I do. I do have a liquivision and fischer cable and have thought of using it, but the oxygauge has been so reliable for me that monitoring ppo2 has been pretty easy. I have two other older o2 monitors for the dolphin, the cochran which is wireless and another that is wired, the HS Explorer. I haven't used it.

    But for the kind of diving i do on rebreather, basically open water (and sometimes a cave dive with proper bailout), I'm happy with manual monitoring of PPO2. and using open circuit dive planning. I modified the dolphin to accept a backplate and wing.

    skip

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    RBW Member skip is an unknown quantity at this point skip's Avatar
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    Re: SCR Dive planning?

    Quote Originally Posted by LLWS  View Original Post
    Explorer Dive Plan: Swim until it tells you to stop swimming. As far as a legit dive plan, it's basically too much trouble due to the number of variables. I use to argue you could easily plan against OC on air, but then we caught the Explorer allowing <air equivalent PO2 depending on DCP so that doesn't work either.
    too much trouble? for a legit dive plan. scary. plan your dive, dive your plan.

    then again, maybe you know way more than me....

    skip

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    Supporting Member darushin is an unknown quantity at this point darushin's Avatar
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    Re: SCR Dive planning?

    Quote Originally Posted by skip  View Original Post
    too much trouble? for a legit dive plan. scary. plan your dive, dive your plan.

    then again, maybe you know way more than me....

    skip
    Unfortunately for the explorer that is the most accurate plan. I was always told plan a dive on it as though it is air. The explorer doesn't work like a typical ESCR/SCR unit in that you don't set a PO2 or adjust your PO2 directly. You set the DCP which is numerical value from 10 to 99 (If my memory is correct) from that it determines from it's own working more or less how much to let the FO2 drift.

    The explorer can also do deco but to quote my instructor, have your will and life insurance paid up before doing it.

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