Choosing my first rebreather SF2 vs JJ

[Herje8990]

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.

I primarily dive in Okinawa where diving in a drysuit is more of a "nice to have". I am not fan of the idea on overweighing my unit for trim. Even with my SF2 in 3mm or 5mm i am about 4-6 LBS too heavy.

 

[Alex Ouroboros]

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.

Hope you get the chance and at less than those prices..

 

[stuartv]

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)

Where is the death O-ring in my rEvo? I have not been able to find one.

 

[Enevoldsen]

I dive an SF2, and are past 100 dives. I love the unit and can not recall all the problems with the unit, mentioned in this post. Yes, it is a little harder to breathe, head straight up or down, but not impossible at all. I do not notice the increased wob anymore. Furthermore the unit is sleek (sdt. version) and exceptionally easy to clean and maintain. It is super dry and the CL is soo easy to drain - if water enters the system. To date i have never flooded the unit. It is super easy to convert to side mount, and it is possible to configure the SF2 in several ways. I dive it with at GUE set up, with 2 x 6.7l carbon tanks as dil out, and a 3l. alu tank for O2, this works perfect for me as i never go deeper than 35 meters (almost impossible in Denmark) as i do a lot of shore diving. Furthermore it is solid as a tank! Feel free to PM me for pics of my set up or questions..

 

[Dsix36]

Hmm how bad would JJ be for air travel? I understand it’s almost 20kg without the tanks and sorbs
I have never had one so I can not tell you more than what I already did.


I understand u must be slightly off trim to have a good/ decent WOB?
You need to be pretty good in trim and horizontal to have a good WOB

 

[justinthedeeps]

@Henry_LKW if you are diving in that drysuit with an undergarment, the JJ-CCR is a good fit.

It can also be lightened (and made more buoyant) by changing to a carbon backplate and alum cylinders. In that config, it is only ~30kg fully rigged, only slightly heavier than a rEvo Micro at ~28kg (I have weighed both rigs, ready-to-dive).

You don't need heavy jetfins for wetsuit diving. I have no trouble using the lighter RK3's--even in a drysuit. If wetsuit diving, fit for a bouyant boot (5 or 7mm) to reduce sinking legs issues.

Smartly padded, the JJ can survive air travel in an ordinary suitcase, leaving room for clothing, regs etc under 23kg. I currently use a Pelican Air 1606 (5.6kg empty), which might be the smallest/lightest that will work, but the stand must be detached. I replaced four small nuts there with SS 316 wingnuts for convenience. I still have not had to fly with any single piece of luggage above 23 kg.

Head piece always in a carry-on, you can buy a lite screw-on head protector for that.

Strong regional support there for JJ in the standard (non-GUE) config, especially in Bali/Gili

The rEvo dives well too, but I still like JJ for its adequate simplicity and overall diving comfort.

 

[rjack321]

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.

This is a normal-ish price for 3-4 day cross-over. I wouldn't expect it to magically decline someday.

Used units are really the way to go until you *really* know what you want

 

[GF99/99]

Pretty spot on!

Also some other things to consider are:

• SF2 resale value = horrible (there is a reason for this, might give you some insight on the unit) but I guess this could be a good thing also if you in the market to buy one second hand.
• JJ resale value = very high. (But like the SF2 on the reverse this makes it difficult to find a used ones for a good price)
• You mentioned you want to dive deep and caves. This will mean long run times. Keep in mind the SF2's CE scrubber rating is only 135min (yeah yeah we know this is conservative but still it is the CE rating) CE rating for JJ axial is 3hr, radial is 4hr, and XRC is 6hr. As you get more experience you can upgrade your scrubber.
• Also the JJ is much easier to configure for "expedition" style diving. Try strapping 4 onboard tanks and a canister light to an SF2 cleanly and easily.
• The JJ has a stand personally for deep diving with 4 bailouts I find with 4 B/O the tanks sit much nicer stand clipped.
• The JJ comes with standard LPI connections for the O2 and dil MAV's for easy plug ins of offboard gas.
• You mention your in Singapore. So another consideration is availability of high quality Mod 1, 2, and 3 instructors near you. I think you will find trying to find this near SG for the SF2 is quit difficult. I think Miko Passi in Koh Tao is the only one I can think of off the top of my head (and sorry nothing against him but the SF2 is not his primary unit) For the JJ you have quite a few include Will Goodman in Gili T who has more hours on a JJ than anyone I know and also a former world record 290+ meter dive on a JJ.

Personally for me the sf2 scrubber rating is such a no go. In warm tropical water using DPV's I am happy to over run the CE scrubber rating but only within reason. It is pretty hard to do a deep dive or solid cave dive in under 4hr. Are you really going to overrun the SF2's scrubber almost twice what the CE rating is??? Yeah yeah im sure there are people doing it but does that really mean its ok . How much is your life worth. Remember a Co2 hit at depth or in a overhead environment would be very hard to recover from.

I dive an SF2, and are past 100 dives. I love the unit and can not recall all the problems with the unit, mentioned in this post. Yes, it is a little harder to breathe, head straight up or down, but not impossible at all. I do not notice the increased wob anymore. Furthermore the unit is sleek (sdt. version) and exceptionally easy to clean and maintain. It is super dry and the CL is soo easy to drain - if water enters the system. To date i have never flooded the unit. It is super easy to convert to side mount, and it is possible to configure the SF2 in several ways. I dive it with at GUE set up, with 2 x 6.7l carbon tanks as dil out, and a 3l. alu tank for O2, this works perfect for me as i never go deeper than 35 meters (almost impossible in Denmark) as i do a lot of shore diving. Furthermore it is solid as a tank! Feel free to PM me for pics of my set up or questions..

As I mentioned above much earlier the biggest problem and the No Go for me on the SF2 is the scrubber. The OP is specifically asking about deep wreck diving. This is basically what the JJ was designed for. Proper deep exploration diving. Yeah sorry the SF2 is not built for that. I like my life too much to be running a CE rated 135min scrubber way over. Ill stick to the JJ 4kg radial XRC scrubber (almost twice the size of the SF2 scrubber) on a 6-8hr deep deco dive.

I think scrubber ratings is one of the most overlooked things people do not take into account when buy a unit. And also during dive planning. What if you have an issue and over stay your bottom time and rack up alot more deco, our you need to do in water recompression, or your in a cave and get lost and now your 6hr dive turns into an 8hr dive, how confident are you in your scrubber???. Usually people are always looking at WOB, CL location, cool fancy features like He sensors, pressure transmitters, etc. But don't forget your life if most dependent on your scrubber. And sorry a 135min CE rating is pretty sad. It is also something that most SF2 instructor do not disclose or like to talk about.

Direct from the SF2 manual pg. 13. Also SF does not like to share the CE test results, you will see that JJ will share them no issue.

 

[Dsix36]

Scrubber duration IS a big deal, whether you want to admit it or not. Most people on RBs will be doing longer dives than they did on OC and may/may not push limits a bit more due to the shear amount of extra time it allows to solve problems if encountered. Case in point - My rEvo is rated at 4.5 hours but I often pushed it to 6 hours since a vast majority of the time was spent relaxing on long deco, but this one time at band camp (really bad day) my planned 5.5 hr dive turned into a 10 hour dive. I am sure glad I could do the entire dive on my scrubber since there was no way I had enough OC bailout gas staged to get me out alive.

 

[rjack321]

But don't forget your life if most dependent on your scrubber. And sorry a 135min CE rating is pretty sad. It is also something that most SF2 instructor do not disclose or like to talk about.

Direct from the SF2 manual pg. 13. Also SF does not like to share the CE test results, you will see that JJ will share them no issue.

well its downright tiny as full sized CCRs go, only 2.2kg. Not a super critical issue in very warm waters but its terrible for <5C kinds of conditions