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Fathom CCR vs JJ-CCR

Discussion in 'Rebreather Diving' started by Madddogggy, Oct 29, 2019.

  1. JonG1

    JonG1 Nassau Grouper

    # of Dives: 2,500 - 4,999
    Location: Glossop UK
    Could someone describe the stock layout of the Fathom pls in terms of MAVs, BOV, whether there is a manifold, if so what it feeds, whether it has QCs etc.

    Website seems reserved for owners.
  2. kensuf

    kensuf Cave Instructor

    There's not really a "stock" layout, except for the following things:

    HUD, Backmount counterlungs, DIL MAV with QC6, O2 MAV with needle valve.

    Most people go with a BOV.

    Some people go with an ADV, which is integrated into the exhale t-piece.
    tbone1004 likes this.
  3. rddvet

    rddvet DIR Practitioner

    # of Dives: 50 - 99
    Location: Florida
    I went with divesoft bov (partly due to not liking golem gears historically bad customer service so i try to boycott them as much as I can) and adv. love the divesoft Bov. Like Ken said everything else comes with it. It’s just adv vs no adv and bov vs Dsv and if bov which one. Even with bov and adv, it was more affordable than most other units I looked at.
  4. Doby45

    Doby45 Do I have something in my teeth?

    I love mine. I went with the shrimp and no ADV. Dives like a dream, but of course I will say that because I paid for one. In all seriousness. I went with the Fathom because first and foremost I wanted a manual, secondly a bunch of my friends dive them, thirdly the unit is basically bulletproof. I only have about 40hrs on my unit so far but it has been awesome to learn and dive on this unit. WOB is great, setup and clean up is not so ridiculous that it becomes a grueling chore. There is flexibility is the configuration of the unit, not so much between backmount and sidemount, but as Ken said you can easily set the unit to dive it off a boat with onboard dil or the standard dilout configuration.
  5. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    This is turning out to be a Fanboys for Fathoms meeting! :D
    And yet, JJ is rather popular. Apart from @doctormike , no one is chiming in for the JJ.

    As another guy slowly heading toward RB, help me learn more. Intellectually, I get the manual vs. solenoid debate (and have actually been contemplating hybrid). But I'm sensing an anti-solenoid tilt in this thread, yet the eCCR's are popular.
    Is it as simple as these varying considerations? Like having the toy run your dive vs having to track your ppO2 drift? Is it how you dive and not wanting the clicking solenoid to mess with your buoyancy during up and down contour following? Is it photographers not wanting to get in trouble when they're concentrating on that shrimp? Is it a legitimate worry about a stuck solenoid?
    Somebody defend the JJ, please (or mention the X-CCR, since I've been looking at that, too).
    FreeFlyFreak likes this.
  6. taimen

    taimen ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Europe
    JJ is sold in one standard configuration (especially in europe due to ce requirements)
    But it allows quite a lot of flexibility for configuration too. It is easy to configure for offboard gasses or larger bm cylinders. GUE config is one good example. BOV kits are available, as well as cmf valves. I like my almost standard configuration, but the options are there.
  7. Jeremy Williams

    Jeremy Williams Nassau Grouper

    @rsingler... As a newb always willing to enter the fray...

    I think of the solenoid on the X as a safety system. Same would be true of the JJ. If the primary system (i.e. YOU) fails, due to your distracting shrimp, the solenoid takes the correct and measured action to maintain a safe PPO2 (a.k.a. the controller set point).

    I will say this... It is MUCH harder to maintain buoyancy if you are relying on the computer to maintain your loop. This is not true on the MCCR because it simply won't. This doesn't mean that it's easy on an MCCR, it's just that the MCCR won't DO anything to make it harder. But flying an ECCR and an MCCR over a sawtooth profile should be about the same level of difficulty if it's done correctly by a well trained diver. It's all about maintaining minimum loop volume and anticipating the loop. It's hard at first and becomes easier with time and experience.

    Some people say that an MCCR makes you more involved in flying the unit and is therefore better, but I think this is a difference in training and mindset than anything else.
    rsingler likes this.
  8. taimen

    taimen ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Europe
    Yes, eCCR is that simple. I think the buoyancy issues due to solenoid action are really overexaggerated by mccr proponents. And you always have the option to set lower setpoint and run manual. I usually run my shallow stops manually, but that is mostly to prevent getting bored. But you have to track the pO2 anyway. That is a valid point against eccr that it is easy to forget.
    My JJ has performed flawlessly this far. I can't praise it any more. The issue with head-body junction is not a deal breaker.
    rjack321 and rsingler like this.
  9. rjack321

    rjack321 Captain

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
    I don't dive a JJ but I do dive a "tube eCCR" which has some similarities - a 2.7 Meg

    For wreck diving I vastly prefer the Meg over my kiss sidewinder but that is mostly due to the BO configuration that the kiss almost demands (2 SM bottles of the same gas)

    I find that manually adding O2 messes with my midwater buoyancy way more than a teaspoon of O2 injected by the solenoid. So when I have 90mins to hang out looking at a line, I pick the Meg for sure. I have never had a stuck solenoid (in 5 yrs) and its not really something I stress about. I am fairly confident (perhaps more than I should be I dunno) that I would quickly detect a stuck solenoid.
    rsingler likes this.
  10. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    I figured it would be obvious, too. But then some YouTube searching gave me this from 2 yrs ago:

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