Fathom CCR vs JJ-CCR

[rjack321]

The head to body junction for the JJ is terrible - especially for cave diving where percolation and crap wants to settle in there so the head is hard to remove. My buddy ripped the threaded screw out of his JJ head. We had to track down a bigger screw before we could rethread the head and get it off the tube.

The string trimmer cord on the Fathom is totally solid and reliable. @Jon Nellis of Genesis DPVs was the first to adopt that latching mechanism and it has since been adopted by UWLD and the Fathom. It works and its corrosion free.

 

[rddvet]

Do you want to travel with your unit? If so, go fathom. Way lighter and easier to pack small than a JJ. Otherwise you’ve gotta figure out what you want. Only proprietary part s on fathom are the head, body, and needle valve. Th rest can be sourced all pver the internet.

JJ and sf2 were the other units I looked at. I persoanlly like the idea of a manual unit. Haven’t done any major diving on a unit with a solenoid. Simplicity is key for me and fathom delivered that more than any other unit.

 

[kensuf]

Fathom.. Cons...

1. Nylon is hydrophilic and I found that after doing back to back days in salt water the nylon lock line would swell enough that I had a hard time feeding it through the channel to lock the lid down. Basically I could get two days in a row out of it, then had to swap with a new one. The swelling went down after a few days, so alternating between two pieces of nylon solved the problem.

2. I find that it's too easy to over-pack the golem scrubber, which makes it difficult to get the lid on. It's worse when diving sofnolime 812 versus intersorb 797.

3. It'd be nice to have a stand on the bottom of the can.

4. Uses JJ style cells rather than R22D's. There are pro's and con's to this, the con being sourcing availability in remote locations. This is resolved by bringing spares with you.

Fathom.. Pros...

1. The unit just works. I've done 8.5 hour dives on the unit and been down to 350' on it. No complaints in either way.

2. Backmounted CL's -- great stuff. Hydrostatic work of breathing in all orientations is very good.

3. The HUD battery lasts a long long time. I'm probably coming due for a replacement soon. I won't tell you how many months that is, but it's longer than my cells.

4. Uses JJ style cells rather than R22D's. I can literally remove the cells and drop the head in a bucket of water for cleaning, couldn't do that with R22D molex cables sticking out of the head. Yes, this is both a pro and a con.

5. Robust mounting brackets can be used with bigger cylinders. I have an ocean rig that back mounts LP50's with LOLA valves onto my Fathom.

6. Needle valve - nicely made.

Fathom.. Neither pro-nor-con

1. mCCR. You either buy into the mCCR concept, or not.

To the best of my knowledge, not many people are diving them in cold water, but there really shouldn't be any problems with it (not any more so than any other unit), and also a couple of new england guys just picked up a few.


JJ..

I can't really say much about the JJ. While I'm pretty familiar with the unit from an intellectual standpoint, I have zero time on one. The pro's include the shearwater electronics with the HUD, the con's include the weight (it can pack up in a carry-on though), and the latch mechanism for the lid (I have seen a number of JJ's take two people to separate when sand/grit gets in there). For a long time I said that I believed the JJ was on my short list for an eCCR, but now I'm not so sure.

 

[rddvet]

..

1. Nylon is hydrophilic and I found that after doing back to back days in salt water the nylon lock line would swell enough that I had a hard time feeding it through the channel to lock the lid down. Basically I could get two days in a row out of it, then had to swap with a new one. The swelling went down after a few days, so alternating between two pieces of nylon solved the problem.

2. I find that it's too easy to over-pack the golem scrubber, which makes it difficult to get the lid on. It's worse when diving sofnolime 812 versus intersorb 797.

1. That's interesting I haven't found that, but we pitched the orange piece for a heavier duty piece of weedwacker string I had in the garage. We dove probably 4-5 hours a day in Bonaire and didn't really rinse our gear off much and didn't have any swelling. Wonder if we were lucky or the thicker string was the trick. This is the weedwacker string that has ridges on one side so it supposedly cuts the grass/weeds better.

2. I thought it was just me. We struggle sometimes. You pack and pack and pack, but then it's just enough to make it impossible to get the lid on. Then you remove a tiny bit and it's too much. It can be frustrating, but every time it gets a little better.

 

[taimen]

Maintenance issues and/or components one should be aware of? Particular mechanical failure points.

First 100 h done with a JJ, my first rebreather, and recently MOD2/CCR cave trained. I don't have any experience with Fathom, which is an interesting unit. I could have considered it if it had any presence over here.
My only gripe with the JJ is its head-body junction. Silt can reach the first head o-ring and if any sand or stone chips go into that junction it is difficult to remove the head. This is annoying. JJs are anyway proven to be very reliable units. Serious problems caused by the badly designed head-body junction seem to be quite rare.
Using a cave shield somewhat protects the junction, but silt still gets in.
Body and frame are rugged and the unit is easy to handle in small boats etc. JJ performs very well in extremely cold conditions (I haven't heard of specific problems with other units either).
Manufacturers don't release any numbers, but JJ is very popular in Northern Europe and the UK. It can be considered quite well established.
From a basic user perspective the manufacturer is quite quiet. They don't publish much information on updates, service bulletins or anything. For example we are told in training that it is not recommended to update Shearwater controller firmware before JJ-CCR has approved the new version. Yet, JJ doesn't publish their latest approved firmware version anywhere. I wonder how information about critical safety related callbacks or upragrades is supposed to reach end users (supposedly through instructors, but I don't know if it is realistic to expect this chain of people to be reliable).
Everybody I know who has dealt directly with the company has reported extremely good service. Parts are shipped express globally immediately and spare heads or units loaned.
I don't see many people using trim weights with JJ, certainly not anyone whose trim I have admired.

 

[doctormike]

I love my JJ. I use the tube weights in salt water/dry suit configuration. Trims great. Have traveled with it a number of times as well, no issues.

I haven't had much trouble with the head/can junction, but it is sometimes a bit tough to open if there is a lot of debris in the water. Pete Mesley has 3D printed these things (check out the JJ FB page if you want to order some from him) to address that problem, and to protect the top of the head.

 

[rjack321]

Do you want to travel with your unit? If so, go fathom. Way lighter and easier to pack small than a JJ. Otherwise you’ve gotta figure out what you want. Only proprietary part s on fathom are the head, body, and needle valve. Th rest can be sourced all pver the internet.

The fathom needle valve is actually a copy of the Chris Kennedy version. Chris is a bit grumpy about that. I guess you could call it proprietary since you aren't going to carry a spare or pick up spare parts at a dive shop. I can't see how it could fail other than the stem packing which could be sourced from swagelock

 

[rddvet]

The fathom needle valve is actually a copy of the Chris Kennedy version. Chris is a bit grumpy about that. I guess you could call it proprietary since you aren't going to carry a spare or pick up spare parts at a dive shop. I can't see how it could fail other than the stem packing which could be sourced from swagelock

I don’t see it failing either, and I believe is fairly user serviceable. I guess the needle valve is somewhat proprietary is more correct.

 

[tbone1004]

The fathom needle valve is actually a copy of the Chris Kennedy version. Chris is a bit grumpy about that. I guess you could call it proprietary since you aren't going to carry a spare or pick up spare parts at a dive shop. I can't see how it could fail other than the stem packing which could be sourced from swagelock

and even then, it's only "proprietary" because it's made specifically for that unit. It's still just a needle MAV, so you can put a Chris Kennedy, KISS, or homebuilt needle on there and it will function exactly the same. They can also go on any eCCR as well and turn it into a hybrid, so that to me is not really a buying point

 

[rjack321]

I don’t see it failing either, and I believe is fairly user serviceable. I guess the needle valve is somewhat proprietary is more correct.

yes and as @tbone1004 says you could even swap it out for a Kiss orifice MAV if you are in a pinch.

Of course that is about as complicated as servicing a jaska solenoid in a JJ (not complicated but not something you are likely to do in the field)