Diving multiple rebreathers...

Mdemon

I've had some excellent advice from people who have dived multiple rebreathers (thanks guys!) and one of the extra tasks appears to be stopping the BOB (Bail Out Breather) from imploding as you descend. There are many suggestions on how best to do this - ADV, Manual inflate, KISS valve etc.

I have a slightly different idea and I'd welcome some of you more experienced BOB guys picking the holes in it for me?

Basically, I'd connect the primary Rebreather (e.g. Inspo) to the secondary, side-mount RB. (This would be fixed fairly tightly to the D-rings to stop it floating about). I'd be connecting the loops and doing it using APD's GCS valves. Not too sure where I'd connect these - it would have to be very robust. Maybe fit a female fitting to the Primary ADV? For the mega-paranoid, there could be a hydrophobic membrane in the BOB GCS to insure against water passing from primary RB to BOB.

Anyway, the theory goes like this:

Decend. ADV kicks in and pressure equalises in primary Rebreather and also the secondary RB via the GCS hoses. Complete dive and ascend. Increase in gas volume vented as usual via primary RB with secondary RB equalising via the GCS hoses again.

The advantage in this case is that it's business as usual, nothing else to play with, just larger volumes of gas going in and out of primary Rebreather. Other advantage is that the independant tins on the secondary RB never get used.

Bailing out:
Operate BOV and go OC. Immediately disconnect GCS hoses - loops are now separate. Secondary Rebreather has very similar gases to primary, so should be immediately breatheable. Close BOV and switch to secondary RB. Monitor PO2 and go home.

Any reasons why this wouldn't work?

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www.southwestmafia.com

It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

finbar.taylor

I'm no expert by a long way but I've bailed due to high, lowPO2 or due to CO2 , I'm still learning to over come the urge to get offthe loop but getting better ;-).


From listening to most of the people on here the only time you get offthe loop is in a full loop flood which has now transfered to yourbailout?

Just my first thoughts


Fin

Mdemon

Hi Finbar,

Yes, that's the biggest risk. However, two things. I don't think the GCS hoses will allow water to pass through that fast, so a quick disconnect will stop the majority of it. Secondly, because WOB isn't an issue, I can put a hydrophobic membrane (maybe even goretex?) across the entry into the BOB, the idea being that the GCS hose may be full, but not the BOB.

What do you think?

__________________
www.southwestmafia.com

It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

dave t

I dont think I understand your use of the quick dissconnect fittings but if you want to dump the loop on the bob then just fit a drysuit auto dump.

I have built a couple of "twinspirations" in my time and that method worked for me.

Also in my experience you will want to go OC in-between moving from the primary rebreather to the bob

HTH

Dave

Mdemon

Thanks Dave! I'd so love a twinspiration... (Lottery ticket purchased, pigs fed etc... )

The GCS fittings allow a sealed disconnect of the hose joining the two loops - that's the only reason for mentioning them. The idea is that gas in the loop from RB1 will equalise across the hose into the loop of BOB. So no ADV needed on BOB and no gas needed from different cylinders. The gas should be very similar at all times, so bailing to BOB shouldn't require much PO2 adjustment. On ascent, the expanding gas will pass back through the hose, rather than venting through a dump valve. Not much advantage to this, just how it would work. I'd probably fit an autodump as you suggest anyway, or unscrew the OPV on the CLs.

There is an OC-phase - using the BOV (OC/DSV). I think you're right - there needs to be some sanity breathing whilst getting the BOB ready to switch to. I use 7li drive cylinders in my Inspo so my OC/DSV (also a Bob, LOL!) would give me a few breaths to get my head together.

Does that explain it better?

__________________
www.southwestmafia.com

It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

dave t

Ok now I understand you, that would only work if the two loops were at equal pressures in the water coloum, i.e it wouldnt work if the bob was carried as a sidemount due to the different pressures on the counterlungs. Also the chance of having really shitty gas in the primary loop (reason for get off real quick) could be transferd to the bob. The loop on the bob needs to be very clean gas for an effiecient switch and to minimise the OC phase.

best

Dave

Decodiver

The GCS hoses are designed to ensure gas flow in only one direction, ie towards the male fitting.

I am not sure what you hope to achieve by this, but of course it would be Darwinesque to have both loops connected IMHO, one loop flood and you will go down in history...as well as the water column...

Personally I am just waiting for the side mounted Ouroboros to appear next year then I'm off.........

Cheers,

Dave.

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CCR/OC Trimix Instructor Trainer
CCR Training to Mixed Gas in Switzerland, France, UK & Germany on
Megalodon/COPIS-Megalodon/KISS/Sport KISS/Ouroboros/rEvo/Inspiration/Evolution/Sentinel

www.zerogravitydiving.com

Rebreather World Terms & Conditions

Mdemon

I think that's the nail in that particular coffin! Lower the BOB and presto! Instant Hamster Cheeks...

LOL! As I said...Lottery ticket bought, fingers crossed...pigs fed and ready to fly.

Thanks for your help all!

__________________
www.southwestmafia.com

It's as easy as abc;

a) "Carry adequate bailout"

b) "If in doubt, bail out"

c) "Always know your PO2"

If you find that hard, stick to crochet.

"Once the agenda-monkeys and perfect-worlders have moved on, perhaps we can do some diving?"

wizbang

To steal some thunder from JDZ and to ask a question or two.

On the weekend JDZ carried his CCR Dolphin as a BOB (while diving OC) to 50 odd. The unit was on and had been pre-breathed (sp) ready to go, loop shut and secured. JDZ got to the bottom and went to the loop.
JDZ found the loop to be perfect, volume wise, even after clearing the DSV as usual. We thought it was a good test and nice to know that the ADV will do its job even when un-manned.

Now to question time.

Assumption one: You are making/using a BOB for deeper dives.
(Dives where OC bailout is restrictive)

For those considering/using a BOB, how do you get your head around only having two x 3l Diluents and two x 3l O2's (at most, some with less) considering you will be at 100M plus. That is not alot of "sanity" breaths from an onboard reg.

next

For those that are considering/using a BOB, have you given any thought to how this affects your use of the BOV. Does this mean you only use the small onboards or do you also carry OC bailout for the BOV.

thanks for the your time.
PS Moderators if you think this is too much of a tangent would you mind splitting this off into another thread. Thanks Wiz

Steve

My thinking is that only taking a small amount of dil to be OC on when initially bailing to the 2nd loop isn't a good plan. having said that, after bailing and during ascent, there isn't a lot of need for dil. Sure you need some but not a lot. Looking at the DIR boys and there tank selection is a good idea. A large OC tank need not be a pain.

As one goes deeper (longer dive) more O2 is required as well. I can't see a shortcut to taking lots of gear other than a risky one.

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