Fathom CCR vs JJ-CCR

[rjack321]

I figured it would be obvious, too. But then some YouTube searching gave me this from 2 yrs ago:

I guess I consider that pretty damn obvious.

But I would have been fixing that a whole lot faster - seizing in front of the camera while showing off your high ppO2 is a bit out of style.

 

[taimen]

Stuck solenoid causes gas flow which most of divers can hear, rise of pO2 which is very fast at least in JJ due to location of cells close to solenoid and finally a buoyancy swing. It should be one of the more easily detectable failure modes in rb diving.

 

[rsingler]

I guess I consider that pretty damn obvious.

But I would have been fixing that a whole lot faster - seizing in front of the camera while showing off your high ppO2 is a bit out of style.

I hear you. But the bailout is not seen on camera, and the text overlay said "he left the circuit and the shipwreck", so I'll presume it was in that order and give him half a pass. But he gets no credit for not noticing. Two separate readouts, but makes me wonder if a Smithers on his DSV might not have been better...

 

[doctormike]

I think the buoyancy issues due to solenoid action are really overexaggerated by mccr proponents....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.

I find that manually adding O2 messes with my midwater buoyancy way more than a teaspoon of O2 injected by the solenoid.

This^

Rob, you know I'm a huge JJ fanboy. It would be great if we could someday do our first dive together on matching CCRs! But since i don't know anything about the Fathom, I haven't said much here.

The solenoid buoyancy thing is a non-issue, as far as I can tell. The only time I notice anything remotely like that is on my shallow 10 foot stop, and then I just switch to low setpoint and keep the PO2 where I want it manually. I will say that there really isn't a single thing about my JJ that I want to change, but I don't do cave diving so I don't know if the sawtooth profile thing is an issue for an eCCR. I actually can't hear my solenoid (I have a high frequency hearing loss), and I started a thread about that at one point.

Whatever CCR you get, you have to always know your PO2. If you are going to forget to do that on an eCCR, you are going to forget it on an mCCR, the difference being that you will (hopefully!) notice the PO2 dropping as your workload increases on the latter. So far (about 160 hours after training), the controller has been good about keeping a setpoint. Doesn't mean that I don't watch it, but it has been working as advertised.

That's a great video, I have actually been in contact with the guy who made it and used it in a lecture. Yes, a solenoid can stick open, but so can a MAV - anyone here dive an APOC?

 

[rjack321]

I hear you. But the bailout is not seen on camera, and the text overlay said "he left the circuit and the shipwreck", so I'll presume it was in that order and give him half a pass. But gets no credit for not noticing. Two separate readouts, but makes me wonder if a Smithers on his DSV might not have been better...

Look at 1:27
He has a standard Meg hud, but look at how low it is relative to his eyeballs. More than the stuck solenoid I would say this is not how you want to be monitoring your ppO2. BUT I don't know how long it had been stuck for. It could have been triggered at 1:07 and ppO2 will climb that fast in 20seconds combined with the descent. So I don't want to be too critical here other than to say that he should have:
1) immediately dil flushed to lower his ppO2
or
2) bailed immediately
then decide how to proceed.

As far as I can tell he exited on the dangerous loop then was on BO

 

[Jeremy Williams]

The solenoid buoyancy thing is a non-issue, as far as I can tell.

I find the issue occurs not on ascent or descent but when you are diving shallow, with the PPO2 just at the set point and have a minimum loop volume. You descend a bit, the ADV fires, then the solenoid starts to fire to catch up, then you start getting a bit floaty, then you are ascending a bit and the loop volume is increasing and the solenoid is firing and... If you are not paying attention, you start heading to the surface.

But none of this happens that way if you are flying the unit above the set point manually.

 

[tbone1004]

@rsingler...

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.

only if you let the eCCR do the management for you. If you have a low setpoint of say 0.7, and you run at 1.0, then the eCCR has much more involvement because there is no constant addition of O2. mCCR's drift very slowly, and if you have a needle valve and set it properly, you almost never need to hit the MAV. With an eCCR running in "parachute mode", you have to do ALL of the O2 addition. Granted it's still only hitting a button every few minutes, but it is IMO an incorrect way to view it. I do also view eCCR's as safer than mCCR's if/when you do get distracted because it will maintain a breathable ppO2. The mCCR can only delay the ppO2 from falling below levels required to maintain consciousness. It obviously was not a huge issue for me as I went from an eCCR to an mCCR, but I certainly wouldn't use mCCR as a buying choice and wouldn't discount an eCCR because of that logic.

On the high ppO2 thing also mentioned. I have a 2.7 meg, with the 2-led hud and it is essentially useless in bright water, you can barely see it so seeing it starting to flash red is likely not something you would see. A NERD would be much better and I would definitely invest in one if I was doing mostly open water diving. In caves it obviously doesn't matter since you can see quite clearly

 

[doctormike]

I find the issue occurs not on ascent or descent but when you are diving shallow, with the PPO2 just at the set point and have a minimum loop volume. You descend a bit, the ADV fires, then the solenoid starts to fire to catch up, then you start getting a bit floaty, then you are ascending a bit and the loop volume is increasing and the solenoid is firing and... If you are not paying attention, you start heading to the surface.

But none of this happens that way if you are flying the unit above the set point manually.

I haven't had any problems like that. When I am at my shallow stop and descend a bit, I don't let the ADV fire. I don't have it isolated (International version, not CE), but it only fires if you inhale against a collapsed loop. I just make up volume with O2 if necessary.

 

[doctormike]

only if you let the eCCR do the management for you. If you have a low setpoint of say 0.7, and you run at 1.0, then the eCCR has much more involvement because there is no constant addition of O2. mCCR's drift very slowly, and if you have a needle valve and set it properly, you almost never need to hit the MAV. With an eCCR running in "parachute mode", you have to do ALL of the O2 addition. Granted it's still only hitting a button every few minutes, but it is IMO an incorrect way to view it. I do also view eCCR's as safer than mCCR's if/when you do get distracted because it will maintain a breathable ppO2. The mCCR can only delay the ppO2 from falling below levels required to maintain consciousness. It obviously was not a huge issue for me as I went from an eCCR to an mCCR, but I certainly wouldn't use mCCR as a buying choice and wouldn't discount an eCCR because of that logic.

Yup, exactly.

I don't know anyone who has done this, but I believe that there is a third party needle valve that you can swap into the JJ MAV, making it a hybrid unit, right?

 

[tbone1004]

Yup, exactly.

I don't know anyone who has done this, but I believe that there is a third party needle valve that you can swap into the JJ MAV, making it a hybrid unit, right?

any of the needle valves can be put on any CCR, granted if you have OTS or TOS lungs with drysuit MAV's it may be a bit more complicated. With the JJ since it has bmcl's, it is quite literally as simple as unscrewing the stock mav, and screwing the needle valve in. Can be a Chris Kennedy, whatever the Fathom is using, the new ones from KISS, etc.

Of note though, the Fathom is still blocking the first stage, or at least was. This was typically only done with a CMF which needed it to maintain constant flow, but with the needle valve it means that you don't need to adjust it as you change depth, only when you change your metabolic consumption *typically workload related*. This can be done on any of them though. I believe the KISS is using a CMF that feeds into a needle valve which also helps stabilize the O2 addition requiring less "futzing" with the needle and IIRC it also has click stops which makes it less prone to being knocked out of setpoint, but also let's you gauge "up one click, down two clicks" type of adjustments.