Fathom CCR vs JJ-CCR

[doctormike]

So what would the operational advantage of making an eCCR into a hybrid? You would let the solenoid act as a backup at a low SP, let the needle valve keep the PO2 decay slow, and you occasionally hit the MAV to maintain your desired PO2?

Is it for people who prefer an mCCR but want the parachute?

 

[rjack321]

Care to speculate?

Leon is kind of like "just learn the system as it was designed to be dove"

"Trusting the orifice" to keep everything stable is fine, but you need to have the disciple to check & manually add. The parachute that may or may not work when you really really need it (because you basically dive with the solenoid off) is a mistake. Paranoid the solenoid is going to go crazy with 2 bad cells? The orifice doesn't solve that, discipline and frequent monitoring solves that. The orifice can make that worse since you may even monitor less. He think hybrids are additional complexity when most fatalities are actually caused by complacency and lack of attention to the basics. Don't make the basics more complicated than they need to be. Having 3 O2 injection methods is about as complex as you can get and all three can potentially fail or do something unintended.

 

[rjack321]

@rsingler Leon has lots of opinions, many of them quite controversial including the addition of O2 on the inhale side of the loop. The backwards loop direction I don't necessarily disagree with since it is the same flow direction as the double hose regulators, but to have the O2 on the inhale side is very strange. I don't disagree with a CMF hybrid being the worst of both worlds though. You add the complexity of a solenoid but never really use it, and you add all of the annoying factors of a CMF which is the blocked first stage *just annoying to begin with, but also depth limiting*, and very high risk of the CMF itself becoming clogged. He hasn't done anything with a needle valve which does remove the two weird bits of a mCCR, and I highly doubt he will.

The flow direction and O2 on the inhale side are just direct descendants of leon's heritage with military units

 

[rddvet]

This is turning out to be a Fanboys for Fathoms meeting!
And yet, JJ is rather popular. Apart from @doctormike , no one is chiming in for the JJ.

As another guy slowly heading toward RB, help me learn more. Intellectually, I get the manual vs. solenoid debate (and have actually been contemplating hybrid). But I'm sensing an anti-solenoid tilt in this thread, yet the eCCR's are popular.
Is it as simple as these varying considerations? Like having the toy run your dive vs having to track your ppO2 drift? Is it how you dive and not wanting the clicking solenoid to mess with your buoyancy during up and down contour following? Is it photographers not wanting to get in trouble when they're concentrating on that shrimp? Is it a legitimate worry about a stuck solenoid?
Somebody defend the JJ, please (or mention the X-CCR, since I've been looking at that, too).

I looked at x-ccr too. I stopped real quick when I saw the price. I don’t think we’re slanting anti-solenoid, there’s just a few of us that love our fathoms. I am personally sold on manual over ECCR. That’s just me. I may eventually change my mind. My requirements were lightweight and easy to travel with, exceptionally simple, easily field repaired even outside of the us, and as few proprietary parts as possible. I actually never wanted to go ccr. Then I was introduced to the fathom and it fell inside the guidelines I would need to switch and is purpose-built for the diving I’ll do. And is also attractive since it can be turned into an all in one unit for boat diving without a separate stand being needed. Though I never boat dive

 

[_Ralph]

Only having dove a 2.7 Meg eCCR I am not getting the solenoid buoyancy issue. If put in a SP of 1.2 it just stays there. I use up 150mL of O2, the SP drops a tiny bit, the solenoid puts it back with way more precision than I could do with the MAV.

Yes if I go up 8ft the ppO2 drops, the solenoid adds, and I am buoyant by not only the expansion of my 3 gas spaces (suit, wing, CLs) but by the O2 addition. But I have to vent something anyway (usually CLs for only going up 8ft) so that fixes my buoyancy despite the O2 addition. I'm not understanding "the solenoid screws up my buoyancy" problem.

Just an observation is all... it wasn’t horrible, just I didn’t know which second the solenoid was adding more O2, causing me to vent somewhere before heading further up in the water column on ascents. If I vented out the loop, then more O2 would be added, repeating the whole process.

I’m sure after a few more dives I’d be not as worried as it appears here about it (I’m not worried the slightest)

_R

 

[jgttrey]

@_Ralph, you get used to managing the solenoid on an eCCR. You learn to anticipate and stay ahead of it, taking it into account. It becomes automatic and those buoyancy struggles go away.

For example, if you descent a little and add DIL to keep up the loop volume, you know that's going to drop the PO2 and the solenoid is going to fire to make it up. So, you get used to adding a little less DIL than you need knowing that shortly you're going to get a little squirt of O2. You just need to stay ahead of the unit mentally and pretty soon it clicks and you don't even think about it.

On ascent, once I get to 60-70 feet, I'll switch to the low setpoint and fly manually if I'm not already doing so, manually keeping PO2 where I want it. Pressure is changing rapidly (relatively) once you get that shallow and so PO2 changes more quickly and buoyancy too. You're doing a lot of venting of the loop. I want to control the timing of the O2 injections myself both in order to control buoyancy and so I can vent loop first, then add O2. New eCCR divers blow through tons of O2 on the ascent phase as the solenoid tries to jam O2 into the loop full of low(ish) PO2 gas, only to be almost immediately vented. Better to manage that yourself, venting out the lowish PO2 gas first, and then adding O2.

Oh, and don't fight the ADV. I keep it off almost all the time. I'll leave it on during descent or (maybe) if I'm in a situation where I'm using both hands and having to do a lot of depth changes and I could use the assist. Otherwise, it's off. Even a little unwanted ADV action is a PITA.

 

[KenGordon]

I have a JJ. It is great. I like if for the heavy construction, I considered an inspiration but the plastic box really put me off. I have taken it on planes.

I don’t find the solenoid upsets my buoyancy.

When I have had to get stuff from JJ is has been easy and cheap. Narked At 90 are about an hour from where I work so possible to visit for servicing.

The only mod on mine is a Divesoft BOV, which I also like.

The top head ring does get mucky with silt and rust. I haven’t had anything make it jam though. There is a technique for getting the head off, press first.

Drying the cells could be easier. Once the head is off you have to be careful how you put it down to avoid stuff sticking to the head o rings. The XCCR is better in that regard.

I’d buy it again.

 

[rjack321]

For example, if you descent a little and add DIL to keep up the loop volume, you know that's going to drop the PO2 and the solenoid is going to fire to make it up. So, you get used to adding a little less DIL than you need knowing that shortly you're going to get a little squirt of O2. You just need to stay ahead of the unit mentally and pretty soon it clicks and you don't even think about it.

Back in my MOD1 my instructor told us, "when you descend and lose volume look at your ppO2 then decide which one to add" That directive has served me pretty well. Using combined BO/dil in the kiss that tends towards the hot side (ppO2 1.0-1.1 on the bottom) has been a bit more difficult to anticipate compared to a <1.0 dil that I use on my meg mostly

 

[doctormike]

There is a technique for getting the head off, press first.

What technique do you use?

Drying the cells could be easier. Once the head is off you have to be careful how you put it down to avoid stuff sticking to the head o rings.

Did you get one of these? Works pretty well.

Also, when I put the head away and don't want to leave the O-ring compressed indefinitely, I use one of these (without the fan).

 

[tbone1004]

The flow direction and O2 on the inhale side are just direct descendants of leon's heritage with military units

I know, but it's still a bit weird. About the only way you can get "right rich" with the loop moving that direction. The double hose regulators are why the military units flow in that direction, let's them start their training in double hoses