Fathom CCR vs JJ-CCR

[rjack321]

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.

My ADV is for sure isolated shallow. If it really needs to be on - like I am doing lots of shallowish ups and downs in a cave like Peacock. Then I run 32% dil and the solenoid isn't playing quite as much catchup just because the ADV fired.

What drives me nuts is using hypoxic dil (like 10/50) on as shallowish dive (90ft or whatever) every time I need volume I need tons of O2 to fix the big ppO2 drop.

 

[kensuf]

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).

Defending the JJ: The JJ's a fine unit. I truly think the only three downsides to it are the weight, the way the head locks into the body, and the orientation of the CL dump when you go to de-water the unit. Everything else about the JJ is really solid and it would easily be on my short list if I was buying another CCR (I already own two and a half).

On the e vs the m debate. It's 100% philosophical. There are pros to both. There are cons to both. I say this as an instructor on an eCCR and an instructor on an mCCR, it's really what mindset you want to buy into.

eCCR pros:
* parachute
* can let it run in auto-pilot

mCCR pros:
* forces good habits in manually flying
* the majority use a leaky valve of some sort (orifice or needle), which can be set that you maintain PO2 at rest with no input.

eCCR cons:
* stuck solenoid (very rare, but I've got a friend that had it happen to him)
* allows people to be lazy, which can bite them in the butt (I have a friend who nearly went hypoxic because his solenoid wasn't firing and he was letting it run in auto-pilot and not paying attention).
* takes batteries, which need to be replaced well in advance of the dive.

mCCR cons:
* if you're seriously task loaded, or otherwise incapacitated, you may forget to add O2 (I once got myself hopeless entangled and couldn't hit my MAV for 5 or 6 minutes. Thankfully I had my O2 flow rate set well on the system, but crap that had me worried, I was about ready to do a DIL flush and let the ADV kick in when I finally got my hands free)
* lack of parachute (see #1 pro on eCCR).

NERD, then?

Oh good lord no. I bought a NERD. Did two dives on it. Sold it.

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.

Fathom still uses a blocked first stage, correct. Factory set to 200 psi, which is good to about 400'. I'm testing using a MK17 instead of the DS4 with a blocked first stage. Been using that for about 6 months, been happy with it too.

 

[_Ralph]

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

This might end up OT at this point, but oh well..


I recently did CCR1 with a JJ this summer.

I dive a Sidekick, not major hours on it yet (work has been pretty busy the past 2 years), but can chime in a few thing I noticed between it and a mCCR

The JJ was easy to dive, and did what it is supposed to do.

I did have more issues with buoyancy than I would have liked with the unit (not crashing around mind you, but not where I would like to be.. ie. stable), I’d like to be able to blame the solenoid on ascents, as I do this manually with the sidekick, letting out a portion of breath while on my MAV, making up part of that volume.

On the JJ, with a hood, I couldn’t hear the solenoid, or any O2 delivery system. I could hear my ADV.

So I really had no idea when the O2 was actually firing, aside to keep the setpoint underwater unless I was directly looking at my handset and seeing the PO2.

I came back home, tossed on the sidekick about a month afterwards (sigh, work gets in the way) and had no issues with buoyancy or anything.... just stayed where I wanted to be.

_R

 

[silent running]

I think the big buoyancy difference between MCCR versus ECCR is if you change depth frequently, like in a cave or if you are a photographer who has to reposition yourself often to get a shot.

If you are diving normal, multi level profiles with no sawtooth, the changes in buoyancy of a mass flow valve MCCR versus an ECCR solenoid design are probably minimal, assuming holding a tight SP is your goal...

 

[rsingler]

Defending the JJ: The JJ's a fine unit. I truly think the only three downsides to it are the weight, the way the head locks into the body, and the orientation of the CL dump when you go to de-water the unit. Everything else about the JJ is really solid and it would easily be on my short list if I was buying another CCR (I already own two and a half).

On the e vs the m debate. It's 100% philosophical. There are pros to both. There are cons to both. I say this as an instructor on an eCCR and an instructor on an mCCR, it's really what mindset you want to buy into.

Thanks for a great summary!
Care to add pro/con for hybrid?

 

[kensuf]

Hybrid... Well, you can fly an eCCR 100% manually (I usually do that). I can easily see running a needle valve on an eCCR as being a wonderful thing. I've got two friends running needle valves on their megs, they love them.

BTW -- I can think of at least one time this summer where I thought to myself that I wish I was on my eCCR -- being yanked from 130' to 70' after shooting a bag in a ripping current. If I was on the eCCR I could have easily vented and let the solenoid maintain my setpoint. I can also think of times recently when I wished I was on my mCCR for the more constant O2 flow/buoyancy control during a photo session.

 

[rsingler]

BTW -- I can think of at least one time this summer where I thought to myself that I wish I was on my eCCR

So...sounds like an eCCR with a needle might have been perfect when you got yanked? (Because with a low setpoint and needle, you would have effectively been mCCR during the photo part)

Do I have this correct?

 

[tbone1004]

@kensuf were you letting the unit drive during said photo shoot or running manual?

 

[rjack321]

So...sounds like an eCCR with a needle might have been perfect when you got yanked? (Because with a low setpoint and needle, you would have effectively been mCCR during the photo part)

Do I have this correct?

Only if you block the 1st stage.
I think people diving with unblocked 1sts with a needle valve are nuts. I tried it and almost killed myself. The flow changes crazy fast with relatively minor depth changes and you need to almost constantly figit with the needle setting. Maybe that's ok with bare hands. But with drygloves, scooter, and/or reel taking up a hand or your attention its nuts. Setting it on the surface for your max depth (like how the pelagian manual outlines) runs the risk of it not staying where you set it after gearing up, or on a deep dive you are needing to near constantly add O2 on the surface because the flow rate is far too low. Just no. Blocking the 1st is 110% the way to go IMHO.

 

[rsingler]

Only if you block the 1st stage.

Yes, definitely. That was my assumption...