Why did you Pick SCR as opposed to CCR

EBT

True enough, but then Im looking at it from a cave perspective. If I make the move, it just means chucking a couple of spare tins into the back of the car to cater for depth variances.

Maybe ocean diving is different there, here we tend to pick a max depth and gas up for that, with fallback plans usually being shallower.

Much as I love ccr, the electronics are still the weakness.

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nicothesailer

Cons. #4 should read Dolphin Only!

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PaulTG2

Can you expand on what,specifically, you don't like about "the electronics"? If that's what is stopping you from going to CCR then examining what the reality of the electronics on the various types of units available might be a better discussion.

-p

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Gary68

My SCR is for cave (homebuild). Our design parameters were:

mechanical system - no electronic parts for any control functions
large onboard bailout
gas efficiency ratio of 6:1 or better
removable (carried like a stage, abandonable, secure and recover)
Trimix capable to at least 330'

There were no commercial units out there that really met our needs so we had to build what we wanted. The large bailout KISS mCCR was the closest but still needed electronics for the user to monitor. The RB80 series types was stable without electronic monitoring but wasn't removable (or available or economical).

Large onboard bailout for us is basically => 200 cuft OC which is a lot to carry so the Rebreather had to be built around a cave rig. It would also be advantageous to be able to use the the bailout as drive gas if needed.

We solved the PPO2 drop issue which allowed us to increase the gas ratio (which also aids on the WOB vs the dump valve) and increase the range of working depths. Since our range is limited by our OC bailout past a certain point additional gas efficiency of the Rebreather is of limited use so we will probably keep to 12-15 to 1 rather then much higher. We can also plug in allowing us to use the RB to multiply any available gas usable withing it's normal use range.

For cave I think we've got an excellent tool but I doubt we'll have a lot of interest from OW divers.

Numpty diver

Scrs are i believe a good start for rebreather divers, you learn discipline patience and many dive skills not found on open circuit.
Would be more advantages to start a ccr course and learn how to fly the unit not trying to master the basics , after all most ccr courses are only 10 hr in water time.
But also a good instructor / agency will take most divers and make them just competant on any ccr .
A ccr is the best way to end up , at present i prefer mccr and i am learning how to use the copis meg.(thanks paul )
Somthing i would love to experiment with is a non diver straight onto a rebreather.
Dean

PaulTG2

Can I ask why what things drove this requirement?

If the electronics don't "control" anything, i.e. just PO2 monitoring with the diver controlling, then is that permissible? Your text suggest you wanted a system the diver didn't have to monitor at all -- is that the reason for no electronics?


Sincerely,

-p

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Paul's first law states that the safety of an activity is determined by how forgiving of mistakes the activity is.

Paul's second law states that the difference between an adventurer and an explorer is whether the doing or the learning comes first.

EBT

Im stifling a chuckle, my kiss has many hundreds of hours on it thanks

I still think its one of the easiest units to dive/maintain, but like all current units you're reliant on galvanic cells and displays.

Dont get me wrong, I love the silence, the ultimate gas efficiency etc, but its just not quite as simple/easy as PASCR. The deco argument falls apart with the right gas mixes available.

Truth be told theres a lot of positives for ccr (dont underestimate warm/moist breathing gas too!), but I dont think its neccessarily as black and white as some zealouts make out

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WD8CDH

I really only think there are 2 uses for SCR:

1. As mentioned, Cave Diving with RMV keyed MCR (like an RB80) but then only with PO2 monitoring.

2. Where the dive plan allows the mix to be AIR and O2 is not available.


After many many hours with SCR, mCCR, and eCCR, my prefered rigs are all mCCR or have been converted to mCCR.

My reccomendation to even a new Rebreather diver would be a CMF mCCR ("KISS" style) with PO2 monitoring.

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Gary68

Reason for no electronic controls is so that the Rebreather doesn't kill you if something gets damp/shorted. For example my old bridge dive computer logged me as reaching 1221' depth in Devil's Ear cave (at a spot about 90' deep).

It's not nice if your electronics decides your PPO2 is to low and starts adding til you tox or to high and hypoxifies you.

Basically: water and electronics don't mix.

A RMV PA-SCR has a predictable FO2 drop. They have an impressive use record in cave exploration. Electronic monitoring is unnecessary. In our design I can hook up a gas and expect the FO2 to be within a couple percent of the gas in the tank without external (or electronic) controls.

I have an installed O2 sensor. If the sensor is reading weird I can purge with fresh gas and test the sensor. If the sensor is wrong and the gas is known good the Rebreather is fine - there is not even a need to worry because there is no way for the device to provide outside a certain range as long as the add and purge keep working.

A simple mechanical RMV add system provides very reliable function and it is obvious when something is not working because it stops providing gas (or bubbles stop coming out on each breath and the add stops cycling). The mCCRs are good too but I would still be trusting the electronics to a much greater extent. We are actually calling our homebuild design a "Fire and Forget" Rebreather because it flys itself without need of user control/monitoring. (Not to say monitoring isn't still an important thing to do.)

Dutchy

I considered it as an inexpensive SAFE alternative for CCR. I'm full of fear when it comes to cells and other electronics and scared to death when on top of that software is involved.
If you do the math right (common sense being a validator for calculations) and adjust the flow right) you can stay alive without relying on those things that seem to have a life of their own.

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