FATHOM Dive Systems Q&A

[TheScubaPanda]

How deep has the Gemini been tested to? Any limitations for deeper diving?

mCCR are basically limited by the O2 Regulator IP. I believe Fathom provides a modified Apeks DS4 to extends the range: mCCR Oxygen Regulator - Fathom Dive Systems

FATHOM mCCR Oxygen Regulator

• Modified Apeks DS4
• Blocked – Uncompensated for use with an mCCR
• Stronger Spring allows for 14-20 bar (205-290 psi) IP for 120-180 msw (400-600 fsw) depth rating.
• Apeks Adjustable Pressure Relief Valve (APRV) for safety
• Mini-SPG

If you really wanted to go deeper than 180 msw, you could do:

• Pick an eCCR instead of an mCCR.
• Unplug the Apeks DS4 and use the needle valve to manage the flow of oxygen. Knowing it will significantly increase your task loading, and you better should have practice in shallower water before planning on doing that.

AFAIK, the Fathom (MK3 & Gemini) are the two mCCRs that will allow you to go the deepest. Namely for two reasons:

• They provide the strongest spring in the O2 Reg out of factory (easy to retrofit on any other mCCR to be honest)
• The needle valve significantly reduce the chance of a clog in the O2 MAV, therefore making needle valve type of mCCR safer with increased O2 IP pressure (less likely to block closed).

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As a note, if you didn't know already everything I already mentioned above... It probably means that you're VERY far from being able to ever do a dive below 180m (how many divers in the world have even crossed that bar ???).

So far in fact that by the time you reach that experience level and desire (if you ever do) you will most likely have multiple machines ahaha
Sooooo ... I wouldn't worry too much about the "depth limitation" of an mCCR to be honest ... It's way past what 99.9% of any CCR diver will ever do ...

 

[PEDiver]

I've really been looking at the Mk III lately but have a question around the diluent. Are most people configuring it with dil offboarded and with the left bottle being used for inflation? Or are people setting it up with dil and O2 onboard with the option to change gas to offboard? Seems like the unit can be configured either way. Curious how most people are diving it.

 

[inquis]

@PEDiver Seems that would depend a lot on open water vs caves. What is your intended environment?

 

[PEDiver]

Seems that would depend a lot on open water vs caves. What is your intended environment?

Primarily for cave diving with the occasional wreck dive.

 

[kensuf]

I've really been looking at the Mk III lately but have a question around the diluent. Are most people configuring it with dil offboarded and with the left bottle being used for inflation? Or are people setting it up with dil and O2 onboard with the option to change gas to offboard? Seems like the unit can be configured either way. Curious how most people are diving it.

The standard config when diving with the 2x 3L bottles is the right bottle is Oxygen, the left bottle is Air used for suit inflation and wing gas. DIL comes from an off-board source, usually the left of two sidemount bottles. I use the Fathom in this config all the time while cave diving. There's redundancy in bailout and DIL by using two sidemount bottles.

In the ocean, I generally tend to convert my Fathom to what is basically the "Tech Rig" - twin LP50s with a LOLA manifold on my back with the rebreather sandwiched in the middle. This provides redundancy between DIL and bailout.

Using the left 3L bottle as a DIL source is not one of the standard configurations and not how the unit was intended to be used. It would take a little bit of extra thought, ex if you're using helium DIL you'll want a separate drysuit bottle and I'm a believer that DIL should have a pressure gauge. However, I think configuring it that way is preferable to "monkey diving" with a single DIL/Bailout source (i.e. slinging an 80 and using that as both your bailout and DIL).

 

[rddvet]

I've really been looking at the Mk III lately but have a question around the diluent. Are most people configuring it with dil offboarded and with the left bottle being used for inflation? Or are people setting it up with dil and O2 onboard with the option to change gas to offboard? Seems like the unit can be configured either way. Curious how most people are diving it.

I think currently the grand majority of orders are for the "tech setup" with onboard 50s. It can be set up with onboard suit gas and onboard oxygen or one less small tank and suitgas comes from your back gas or a dir inflation bottle on the backplate. I've always dove with sm'ed bail out. My wife prefers the tech setup (with only one oxygen bottle and she'll use a suit bottle in the dir configuration for trimix). I bought a spare fathom canister that's set up for 50s and both a suit inflation and oxygen bottle onboard. Sadly I bought it a year ago and still haven't dove it because I've been mostly out of the water the past 18 months after having a pfo closure and then life getting in the way.

Edit: missed the onboard dil. I don't know of anyone using onboard dil. I'm sure it's doable, but one of the selling points for me was offboarding dil. I think it's a much better solution, esp if you have a bov. A small dil bottle will not last long if you take a CO2 hit or are at any significant depth.

 

[PEDiver]

The standard config when diving with the 2x 3L bottles is the right bottle is Oxygen, the left bottle is Air used for suit inflation and wing gas. DIL comes from an off-board source, usually the left of two sidemount bottles. I use the Fathom in this config all the time while cave diving. There's redundancy in bailout and DIL by using two sidemount bottles.

In the ocean, I generally tend to convert my Fathom to what is basically the "Tech Rig" - twin LP50s with a LOLA manifold on my back with the rebreather sandwiched in the middle. This provides redundancy between DIL and bailout.

I like the redundancy aspect of offboard dil in a sidemount configuration. And as @rddvet mentioned, using a BOV plumbed into one of those bottles makes more sense than a small onboard bottle. I'm coming from experience on the Choptima which I alternated between SM and BM bailout. I dive doubles 90% of the time and usually have a small inflation bottle on my backplate so was thinking through the most logical configuration. I also love the ability to BM the 50s for ocean diving.

 

[PEDiver]

Edit: missed the onboard dil. I don't know of anyone using onboard dil. I'm sure it's doable, but one of the selling points for me was offboarding dil. I think it's a much better solution, esp if you have a bov. A small dil bottle will not last long if you take a CO2 hit or are at any significant depth.

Agreed, I can definitely see the advantages of offboarding dil, especially with a BOV (which is the direction I am leaning). Since I primarily dive BM with a small inflation bottle on my backplate, the idea of having the onboard bottle used for inflation instead of dil was something new to me.

 

[rddvet]

I like the redundancy aspect of offboard dil in a sidemount configuration. And as @rddvet mentioned, using a BOV plumbed into one of those bottles makes more sense than a small onboard bottle. I'm coming from experience on the Choptima which I alternated between SM and BM bailout. I dive doubles 90% of the time and usually have a small inflation bottle on my backplate so was thinking through the most logical configuration. I also love the ability to BM the 50s for ocean diving.

It kind of falls back on the sm vs bm being safer. I think in reality, onboard 50s are just as safe as sm bailout. If I lose a tank either way I'm still just ending the dive. Sure with sm bailout the tanks are completely isolated from each other, but I see lola'd 50s just as completely isolated. (I'm sure that will be debated by some, but it's just a matter of opinion). I do think the cool thing with the choptima is the ability to do sm or bm on the same unit very easily. Much like I find being able to do sm or bm on the fathom to be pretty easy to go back and forth with, though the choptima definitely makes it a little easier.
I've slowly been falling out of love with sm bailout. I'm happy I chose my fathom over something else since I can easily do either. SM bailout is great, but when you start adding multiple stages BM is easier. Having a second can wasn't the world's cheapest investment, but it makes life easy and unfortunately I'm always happy to shell out money to fathom because I've never been disappointed.

 

[kensuf]

I like the redundancy aspect of offboard dil in a sidemount configuration. And as @rddvet mentioned, using a BOV plumbed into one of those bottles makes more sense than a small onboard bottle. I'm coming from experience on the Choptima which I alternated between SM and BM bailout. I dive doubles 90% of the time and usually have a small inflation bottle on my backplate so was thinking through the most logical configuration. I also love the ability to BM the 50s for ocean diving.

If you'd like to see either of the configs in action sometime, I'd be happy to show you the setup. There's an updated version of the "tech rig" from what I use that works REALLY REALLY well, but you lose the ability to easily convert between the two and need two cans. Still, that's not a big deal at the end of the day and it is a better way to go.