Choosing my first rebreather SF2 vs JJ

[Wibble]

4. If you are looking to dive CAVE or WRECK in the future you might consider getting the sidemount conversion kit. the conversion kit is not cheap (MSRP $4000).

Wow, that’s expensive for what is essentially a bag of hoses and clips!

I considered crossing over to JJ for a while until I realized its not an ideal unit for wetsuit diving.

It’s difficult to “lighten” a heavy unit. There are other lighter weight rebreathers available.

My personal opinion on WOB, in any CCR if you have ****** trim the WOB sucks.

Most rebreathers have the counterlungs much closer to the lungs than the SF2 which places the counterlungs/bellows at the base of the spine and makes the work of breathing far worse when vertical—always at the beginning and end of a dive.

 

[Herje8990]

Wow, that’s expensive for what is essentially a bag of hoses and clips!

It’s difficult to “lighten” a heavy unit. There are other lighter weight rebreathers available.

Most rebreathers have the counterlungs much closer to the lungs than the SF2 which places the counterlungs/bellows at the base of the spine and makes the work of breathing far worse when vertical—always at the beginning and end of a dive.

The new kit has a lot more than just hoses and clips. but i agree its a lot of money for a "conversion kit"

Vertical WOB definitely terrible but manageable,

 

[stuartv]

My personal opinion on WOB, in any CCR if you have ****** trim the WOB sucks.

What other CCRs do you have experience with besides the SF2?

There are definitely trim positions where my rEvo does not breathe all that great.

But, I have not found a trim position yet where the Choptima does not breathe very well. I don't know. Maybe if I literally just laid on my back. But, anywhere from head up to head down vertical to any face down position in between, it breathes great.

 

[Heat Miser]

rEvo instructor and also Choptima diver here.

congrats I hadn't seen that

 

[Herje8990]

What other CCRs do you have experience with besides the SF2?

There are definitely trim positions where my rEvo does not breathe all that great.

But, I have not found a trim position yet where the Choptima does not breathe very well. I don't know. Maybe if I literally just laid on my back. But, anywhere from head up to head down vertical to any face down position in between, it breathes great.

I only have experience in SF2, i am just referencing other CCRs divers I've been diving with like Triton, Liberty FMCL, BMCL, REVO. I do hear great things about Choptima. i guess my point was is there such thing as a "perfect one"?

Honestly, after about 100 hours of diving my SF2 i finally have everything dialed down and I am comfortable on the unit.

 

[stuartv]

I only have experience in SF2, i am just referencing other CCRs divers I've been diving with like Triton, Liberty FMCL, BMCL, REVO. I do hear great things about Choptima. i guess my point was is there such thing as a "perfect one"?

Honestly, after about 100 hours of diving my SF2 i finally have everything dialed down and I am comfortable on the unit.

I have not found a perfect CCR for me. That is for sure. But, you specifically said all CCRs breathe badly when you have bad trim. That part is what I don't necessarily think is true.

Unfortunately, really good breathing seems to always come at the expense of "chest clutter", which I really don't like. So, the Choptima is far from what I would call the "perfect one".

My rEvo breathes well in trim that is slightly head up. But, when I go to actually perfectly flat trim - shoulders to hips to knees in a flat horizontal line, then it does not breathe so well. It's okay for a few minutes at a time. But, if I stay like that for an hour, I'll start sucking wind.

Funny enough, I see MANY people who think they're in good trim and would even go so far as to criticize others' trim. And yet, their trim is actually slightly head up. With their arms hanging down, it's their elbows, not their shoulders, that make a horizontal line with their knees.

I have not tried an SF2, but I suspect that it's like the rEvo only worse (because the counterlung is even further from your actual lungs). When you are actually in FLAT trim, I suspect that it breathes even a little worse than the rEvo. But, when you're in what I learned to call "cave trim" (i.e. top of head level with top of fins, which means slightly head up, versus perfectly flat), then it probably does breathe just fine.

 

[Alex Ouroboros]

I only have experience in SF2, i am just referencing other CCRs divers I've been diving with like Triton, Liberty FMCL, BMCL, REVO. I do hear great things about Choptima. i guess my point was is there such thing as a "perfect one"?

Honestly, after about 100 hours of diving my SF2 i finally have everything dialed down and I am comfortable on the unit.

There is no perfect rebreather, it’s inherent that they all have a death ring (o ring that keeps scrubbed and un scrubbed gasses apart) and all have to use a diaphragm or lung set up that is not actually inside the human body, therefore there must always be a good and bad trim position for breathing,

If anyone tells you a rebreather (usually the one they own,, sometimes the only one they have ever dived) is better than everything else they are talking complete “England football team” yes some are better, some are awful, the best guide to a complete novice that is 100% impartial is look at resale value…. SF2, Poseidon, then look up JJ, XCCR,

Just saying.

 

[rsingler]

I considered crossing over to JJ for a while until I realized its not an ideal unit for wetsuit diving.

I did my MOD1 in Key Largo in a JJ with the stock steel B/P in a 3mm wetsuit.
I still needed to add 2# to the tops of my 3l tanks for trim, because I was leg heavy (no problem with subsequent drysuit). I'm 70kg; 1.75m - your average male.
In the water, JJ is NOT a heavy CCR. And out of the water, its rep as a heavy unit is really exaggerated.
Maybe in the GUE setup with dual LP50's, but that's not my config.

 

[mr_v]

I would not discount a JJ due to its weight. You can trim any rebreather, but some units trim out easier than others. Also, consider these points:

• Unless your neck is exceptionally flexible, you will lift your upper body to look forward and become slightly out of trim.
• According to GUE CCR Cave standards, a diver must “Demonstrate good buoyancy and trim, i.e., approximate reference is a maximum of 20 degrees off horizontal while remaining within 3 ft/1 m of a target depth.” (GUE General Training Standards, Policies, and Procedures Excerpt from Version 9.2 view the full document at www.gue.com/standards.)

Using these standards as a guide, it may be okay to be 16-19 inches off the horizontal plane if you are six feet tall. The calculation uses knees-to-head distance for the body length, as knees are usually bent.

 

[Herje8990]

y, really good breathing seems to always come at t

There is no perfect rebreather, it’s inherent that they all have a death ring (o ring that keeps scrubbed and un scrubbed gasses apart) and all have to use a diaphragm or lung set up that is not actually inside the human body, therefore there must always be a good and bad trim position for breathing,

If anyone tells you a rebreather (usually the one they own,, sometimes the only one they have ever dived) is better than everything else they are talking complete “England football team” yes some are better, some are awful, the best guide to a complete novice that is 100% impartial is look at resale value…. SF2, Poseidon, then look up JJ, XCCR,

Just saying.

One day if there is a JJ instructor close by, I'll take a crossover course to JJ and feel it for myself. So far, the instructors I reached out to wanted me to teach MOD 1 all over again for $1500 or more. the recertification process on a new unit is whats holding me back.