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Thread: BOB Elecronics

  1. #1
    RBW Member AQUANOMAD is an unknown quantity at this point AQUANOMAD's Avatar
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    BOB Elecronics

    I'm getting ready to add new electronics to my FLEX. I will be using it for my deep dives as a Bob along with my rEvo. I'll dive it as a primary sm system as well here and there to burn through the sorb and maintain proficiency. I use a Ratio IDiv Reb as a back up computer. The head has a solenoid installed which I wont be using.
    I have noticed a few guys have opted for the rEvo Dream as a singular po2 monitor (paging Dsix36). I'm considering this route as I like the hud/ monitor combo and I'm familiar with it already. The main thing I'm struggling with is the 2 sensor limitation. Whats the justification of going this route rather than a traditional 3 cell? I know voting logic is mute as its not driving a solenoid but still. The other issue is no onboard deco. A used dream can be had for $300ish while a used Predator Ext runs $600-$750 but no hud. I have a Predator controller I could install on it as a monitor and replace it with a Nerd for my rEvo. Thoughts?

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    Re: BOB Elecronics

    To consider: if you want 3 cell monitoring, solenoid control, HUD and deco computer included maybe have a look at the AV-UWT AV1c at about the same price as a Petrel EXT. If you want a deco computer with 3 cell monitoring (not sure about the HUD option) they have the AV1f considerably cheaper.

    Three cell monitoring for automated voting gives a better chance of identifying the correct cell as failed and to ignore if things get out of whack.

    But in a manual setup, you have a much better system for identifying the dodgy cell (ie your brain and hands). By doing a dil flush and/or spiking the PPO2 a bit higher you can check to see how two cells are tracking with changes and whether one is limited or not, then make your decision accordingly.

  3. #3
    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: BOB Elecronics

    personally i wouldnt have electronics in a bob.

    in my view a bob should be as simple and therefore as reliable as possible. id even go as far as suggest semiclosed.

    the bob i built and used on my dives had three cells and was manual, no solenoid. sometimes i dived it with one cell, id be happy with none.

    the point being on a dive that justifies taking a bob its going to be deep so your dil ppo2 is going to give more than adequate ppo2 the number and volume of 02 adds would be small and easily doable manually. on a deep dive you need the bob to help during the deep or long sections of the dive where carrying or staing tanks would be difficult. during ascent its easy to stage and less vol needed so again a bob is really in my view for bottom/deep sections. relying on a bob on shallower dives or dives where you can easily carry or stage oc but dont in preference to taking a bob....is not in my view a wise idea..... when you run scenarios for deep dives the bottom ppo2 has little effect to deco, dill fo2 would likely be close to setpoint at depth. only on ascent would i bother with o2 addition and that can be done easily during ascent deco as needed.

    i personally think a bob should be really as simple as hell. either semiclosed or manual add.

    initially i thought i needed to keep the loop warm by occasionally breathing from it but soon discovered that biggest risk to losing use of bob through flooding is doing regular switches in attempt to keep sorb warm. after several screw ups i quickly changed protocol to not trying to keep the bob warm and simply running semiclosed (nose venting) during the initial part of bail and so giving the sorb time to activate. i can confirm this works.


    as an aside, i found biggest problem with a bob was always keeping it from flooding by preventing any neg pressure. an adv wasnt reliable enough to do this i found.

    eventually i started using the bob CLs as my main bouyancy (along with a bit of wing) this helped a great deal as the deeper i go id have to add gas for neutral bouyancy, still need the adv but it helps better gaurantee you never develop a neg pressure in the bob

    ymmv but personally when ive bailed at depth i am not going to be injecting o2 to "spike" my cells to check them.....you will end up with a massive ppo2 and have to flush dill....more buggering around during a stress event when your dil fo2 would give you enough ppo2 at depth. id run nose vent semiclosed off a manual system fully aware that until i get to shallower depths it will make sod all difference to my deco.
    Last edited by Drmike; 12th April 2017 at 08:49.

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    RBW Member AQUANOMAD is an unknown quantity at this point AQUANOMAD's Avatar
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    Re: BOB Elecronics

    Maybe I mis phrased that. By electronics I meant po2 monitor. Be it a simple monitor like a dream or something that integrates deco like a Shearwater. Definitely have no interest in electronically controlled. Was mainly after what others are doing for po2 monitoring and justification on going with 2 cell monitors like the dream. Had a good exchange with Dsix36 about it and looking at an AV or Gorilla hud now.
    Agree with most of your post though. Simplicity is the goal, I have a shed full of b/o bottles and no interest on diving this configuration shallow. Its strictly for my sub 80m dives. I dont have the luxury of staging tanks on the line for the shallows. ALL of my diving is solo and I'm on the dpv trigger exploring through out deco. I have heard good things about the FLEX adv sufficiently triggering to keep the cls from flooding but I can always reach down and hit the button too. I will likely go this route and refit the mav later if I need it. Never really considered making it a permanent semi closed but I guess its always a tool in the box if needed.

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    RBW Member Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike has a reputation beyond repute Drmike's Avatar
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    Re: BOB Elecronics

    sounds good!

    bare in mind for an adv to fire there needs to be a negative.

    so your loop will be negative all the time


    i found on long deep dives that the bob would always flood with just an adv.

    keeping the bob positive all the time or at least more of the time seemed to me to make a lot of sense


    ymmv

    have fun!
    Last edited by Drmike; 14th April 2017 at 01:25.

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    Supporting Member Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36 has a reputation beyond repute Dsix36's Avatar
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    Re: BOB Elecronics

    Drmike is one of the people that shared advice and experience with me prior to and during my BOB build. He is absolutely right about an ADV being a possible issue for flooding. I flooded mine a couple of times during the test dives before I got the adjustment fine tuned.

    I use only the ADV for counter lung volume and it has been working extremely well for me. Today was another 4 hour dive to a max depth of 97 foot and BOB was a complete success. I have been relying on it for all of my "bigger" dives for a while now and like to keep skills and muscle memory sharp with practice even on the "little" dives some times too.

    The ADV position and adjustment are critical both to prevent unwanted inflation and the flooding the Drmike is speaking of. It is a very fine balancing act and mine is set a bit too sensitive since I prefer no not have it flood

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    Re: BOB Elecronics

    What I like about 2 cells is the simplicity. They dont agree, I'm bailing out. No guessing, dil flush, pressing handset buttons etc, just bail and exit, don't waste time / resources. I can do that on deco / in the shallows when I'm at relatively low risk, or better on the surface... Yes 3 cells offer a > probability of knowing which cell is off, but no guarantee, and there are cases when the 2 cells are wrong...

    With a bob, there's less reason to worry about bailing out, i.e. time, gas volumes, gas cost etc, just do it and exit. I only need to know the bob is working...

    Some setups have common O2/Dil, i wouldn't want to be flushing, chewing up gas and time at deep depth, and psychological clock a long way in.
    Get bailed, get calm, get out.
    Personally I don't like setups with common paths at all - too much single point of failure probability for my liking. Bill Stone did a LOT of thinking / calculating of that sort of thing...

    Interesting point on O2 spiking...

    My experience with ADV's / mouthpieces has been very different. No issues with flooding, I like swapping several times on descent / ascent (to maintain PPO2) to know the units working by the time I get to depth, and to avoid/detect flooding early when I can abort...
    Yes its task loading / fiddly, but I consider that my lack of skill / ability / practice. Hard to hit high descent / ascent speeds, perhaps thats an issue deeper / for some caves / profiles... But I didn't choose to dive rb to rush a dive, thats just increasing my risk, I'd rather go slow and see less of the cave / deal with the deco time and the cold. Personal choice / I'm not an explorer so maybe at a certain depth / distance etc the risk / benefit equation changes...

    Dealing with multiple cylinders and the buyoancy / streamling can be as much / more work. If it isnt, then stick with the OC bailout...

    Caveat, I havent scootered enough with this config to have an informed opinion....

    Semi closed for deep / bottom / level exit does seem like a practical / interesting choice. It doesnt seem right for deco / for complex cave profiles where i want to get out in a hurry. Eccr seems better when task loaded / easily / frequently distracted / for simple linear ascent, Mccr seems to have the edge for multi level profiles in terms of gas economy and ease of PO2 adjustment...

    Reliability and redundancy, NOT simplicity of the bob seems to be key (if it doesn't work you're basically DEAD), but to me that depends on quality, design, pre dive checks, maintenance, number of failure points, seals etc, not really about 2 vs 3 cells.
    I think simplicity of operation is more important when stressed than simplicity of design, but maybe thats just me.
    Really want to have a look @ Bill Stone's Wakulla book for this...

    I know of many failures where people have attempted to stage rebreathers, but NONE of anyone successfully / reliably staging them, whereas OC staging has been proven to work.
    For me, that translates to I DON'T want to rely on a BoB thats not regularly / repeatedly switched too / tested on the dive...

    I found on ascent, in practice as long as I dont let the PO2 of the BOB fall below 1.0, the deco difference between my 2 units doesnt get too far out of sync, and I can switch units / tweak the PO2's on deco stops / in the shallows to manage the deco withing 5 mins even for multi hour dives...

    For more complex (multi level) / bigger profiles I like real time / integrated deco, when it goes wrong, I don't want to assume my decos based on an inaccurate/assumed PO2...

    For HUGE dive(s) that I've never done, perhaps fixed / max deco is a simpler strategy...

    Interested to hear in more detail about other users descent / ascent protocols for BoB's, ALWAYS willing to learn...
    Last edited by gallathan; 14th April 2017 at 21:17.

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