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Thread: Sidemount BOB - Dive Protocol - How To????

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    RBW Member Dive Africa is an unknown quantity at this point Dive Africa's Avatar
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    Question Sidemount BOB - Dive Protocol - How To????

    Hey

    I suppose like most Tek Divers getting to a certain point (I have been asking this question in my head for a while) the logistics and shear bulk of multiple side-slings in the water gets to the point were we have all considered a BOB (Bail-out-breather).

    My number om my regular dive mates have emigrated and I am finding myself doing more and more solo diving (in the caves in any event) so the shear amount of kit is becoming a real PITA.

    On Deep ocean diving we mange up to five ali 80's (each) on a dive and on deep cave up to 8 (on multiple staged dives).

    Some background on me: I have been a tek and cave diver for more than 10 years and a meg trimix rebreather diver for going on 8 years. I dive both deep wrecks and deep caves (and everything in between when I get the opportunity ) a lot of our exploration happens in the 100m to 125m (330 - 450ft) range and sometimes we venture a little deeper so when I am asking about protocol it is using a BOB to get to these depths and back.

    I am not really interested in the use of twin megs and the like - simple due to the facts that these set-ups are just to bulky and although they allow for deep diving they do not allow for any form of penetration at depth - whether it is cave or wrecks so a sidemount BOB (I need to be able to unclip BOB to push through restrictions)with my normal backmounted Meg is the appropriated set up for me.

    My logic tells me that I'll be diving the BOB (whether it is a Flex/Sidekick/SF2/loki/Homebuilt) and 2l O2 on left with and an ali 80 (maybe ali 40) for dil on right - understanding WOB at depth and CO2 hits I prefer to have a some gas with me rather than just 2l of Dil. I can live with this amount of stuff to carry.

    So here is my Questions:
    1) How do I make sure that my BOB's is breathable at all time/depths?

    2) Does 1) add so much to Task Loading that it is better leaving BOB at home? (on the way down (I assume dill to be added at the risk of flooding the machine (different machines would have different flood tolerances?)- on bottom (I assume on bottom very little to be done) - on assent (I assume a lot of gas to be vent)

    3) Because of the depth the Dil (say a 6/75) will be Hypoxic (in the shallows) - On the ascent how do you manage the gas in the BOB? - I assume at the shallower deco stops you'll swap to the BOB almost at every stop to make the gas in the BOB breathable but do you also take/stage a Hyperoxic Bailout gas with? Say a Nx50 or such? Other than in sumps staging some gas is easy. But what would minimum save protocol be? Or am I know planning for multiple failures? My main concern is a CO2 hit (not that I have ever had one, but hey...)- if you have to bailout to another rebreather the machine may not have the capability to scrub enough gas fast enough and rebreather (especially a BOB will not bring the WOB down to help alleviate the CO2 hit where open circuit might.

    4) eCCR vs mCCR - How does the O2 management on these work - yes I understand eCCR has solenoid and mCCR has leaky valve and/or a manual add and understand and have dived these machines in normal dive applications - but how do you dive them as BOB - I assume you close O2 on both and only open O2 when you actively want to manage gas "type" in loop?? - but please advise/explain??

    4) Ignoring cost what is the best kit for my application?

    5) OK I might have a budget - would your advise to 4 change?

    6) Any other practical advise and words of caution????

    Much appreciated

    Dries

  2. #2
    Mature mouth breather silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running has a reputation beyond repute silent running's Avatar
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    Re: Sidemount BOB - Dive Protocol - How To????

    Hello Dries, I'm not much into the deeper stuff, but I have thought about the issues you mention and I think there is no way around the extra tasking involved with keeping two loops breathable, both PO2 and volume wise. The question then becomes how to minimize these tasks and the associated risks. I think opening and closing and removing 2 DSVs from your mouth during a descent in a dark, cold ocean or cave brings constant risk of catastrophe which would be solved by something like this:

    http://www.ccrexplorers.com/showthre...ight=Dual+loop

    As you will see, somebody inevitably brings up the lack of true redundancy, but clearly with the amount of gear needed for any +100m dive, you are already having to make compromises in comfort and complexity. I don't see a perfect solution, just choices between lesser and greater risk. I would rather get comfortable with a simple, repetitive muscle memory routine of descending a few feet, switching the lever between loops adding dil, breathing and checking PO2. All the while, the DSV never leaves your mouth. I think a leaky needle valve would be manageable on both CCRs considering there are usually two settings, one for descent and one for ascent, with a few minor tweaks along the way. In fact, managing buoyancy/stops during ascent might be easier with an adjustable CMF, instead of two solenoids constantly adding gas.

    As for CO2, if your WOB is good given your dil choice, I don't see a problem unless there would be prolonged exertion at depth. And with the above dual loop, you have the option of fresh BOV gas, or going to the other loop. And if the CO2 shit hits the fan, you can breathe through your dil gas, begin ascent and switch back to CC as you ascend and PCO2 decreases, the dive is over anyway and you won't need dil for the ascent. You could carry doubles on your back with dil and a richer mix for BO during ascent and two side mount MCCRs with 3L O2 strapped outboard on the side mount MCCRs. Make any sense? Just my non deep diving, but still interested opinion... -Andy
    Last edited by silent running; 30th August 2016 at 14:25.

  3. #3
    RBW Member michael-fisch is on a distinguished road michael-fisch is on a distinguished road michael-fisch's Avatar
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    Re: Sidemount BOB - Dive Protocol - How To????

    I've been using a Flex BOB as a totally manual CCR since the middle of March. I've posted pictures of the Rig, tanks etc several times on RBW since the fall of last year.
    Getting used to diving it sidemount, along with a backmounted SF2 has not been an easy journey but I'm comfortable enough to use it in a cave, not so sure that I'd want to use it yet for a freewater ascent from deep wreck dives including lots of deco without a SMB. I am happier breathing the Flex with GG sidemount DSV/Cooper Hoses than I am breathing the SF2 with GolemGear DSV and Cooper Hoses though.

    Michael

  4. #4
    RBW Member michael-fisch is on a distinguished road michael-fisch is on a distinguished road michael-fisch's Avatar
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    Re: Sidemount BOB - Dive Protocol - How To????

    No leaky valve, needle valve or solenoid on the BOB, the only auto on the unit is the ADV for diluent. A 1 second push on the O2 button on the 2 button MAV will take the O2 from below 0.3 to around 1.2, and then you're on your own, if you like to ignore what the Shearwater is telling you about your PO2s, please buy lots of Life Insurance for the wife and kids, or learn to adjust your PO2 around every minute while you are breathing it.

    Michael

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