SF2 vs JJ vs Liberty

[Evan Davies]

If you want crossover to a new unit I don't see any reason not to buy one but
Why not just stick with the SF2? What don't you like about it?

Don't get me wrong at all, I really like the SF2. I just dpn't really have any experience with other units so therefore I assumed my knowledge would be quite narrow. I don't want to make the mistake many have told me of to buy your own unit before you've tried others. So I just wanted to hear advice from others!

 

[rjack321]

I would get a backmounted unit and dive it a lot and not worry about SM CCR.

The liberty and sf2 are actually pretty different than their backmounted versions so you would still probably want a crossover course even if you started with one of those in backmount configuration. I'm guessing you are more likely to add a completely new SM unit in the future vs swap one unit into different configurations back and forth.

The liberty is very complicated for my tastes.
Not a big fan of the carbon fiber tube in the SF2 nor the counterlung on your butt
The JJ is more aligned with what I prefer in a backmount CCR even if it has a few weak points
I like the megalodon with all shearwater electronics and its comparable to the JJ for me in the good/poor balance.
The IQsub offerings are solid even if the xCCR is rather complicated. I would look at the Defender though.

The kiss classic is quite popular in germany despite not having CE, and a solid contender as well
Revo has some strong parts and a few more weak spots (not modular, not flood tolerant, not great WOB, the counterlung is a huge pain, heavy)
Not a fan of the AP units with the weaknesses outweighing the strengths
Not a fan of the hollis prism

 

[FIGJAM007]

I would get a backmounted unit and dive it a lot and not worry about SM CCR.

The liberty and sf2 are actually pretty different than their backmounted versions so you would still probably want a crossover course even if you started with one of those in backmount configuration. I'm guessing you are more likely to add a completely new SM unit in the future vs swap one unit into different configurations back and forth.

The liberty is very complicated for my tastes.
Not a big fan of the carbon fiber tube in the SF2 nor the counterlung on your butt
The JJ is more aligned with what I prefer in a backmount CCR even if it has a few weak points
I like the megalodon with all shearwater electronics and its comparable to the JJ for me in the good/poor balance.
The IQsub offerings are solid even if the xCCR is rather complicated. I would look at the Defender though.

The kiss classic is quite popular in germany despite not having CE, and a solid contender as well
Revo has some strong parts and a few more weak spots (not modular, not flood tolerant, not great WOB, the counterlung is a huge pain, heavy)
Not a fan of the AP units with the weaknesses outweighing the strengths
Not a fan of the hollis prism

What is complicated about the xccr? From comparing specs and engineering. objectively Its a better generation of the megalodon rebreather that doesnt rust (delrin can vs alloy), better ADV, bayonet head and removable cell holder, one of the best bov's, c02 sensor, hp sensors in the head.

 

[rjack321]

Delrin cans can warp in heat, aluminum is fine and tough and no it doesnt rust which is why the JJ is aluminum too.
Co2 sensor is not necessary IMO, complicated, potentially leads to pushing the scrubber, and lastly its crazy expensive
The Meg ADV is genius in its simplicity, I dont think the xCCR can improve on that.
The Shrimp is a nice BOV, but best? Best at what and compared to what?

 

[sea_ledford]

If sidemount is important to you, SF2 and Liberty are at opposite ends of the complicated spectrum. I went with SF2 due to it being one of the simplest (regarding electronics) eCCR designs.

The Liberty has the He sensors and associated backup PO2 calculations... don't remember how many O2 cells it has. But just seemed too complicated for my taste. There are a bunch of things I like about the liberty, but the electronics takes it off my list.

Diving the SF2 sidemount is an interesting challenge to get the hang of. Once you get to keeping it at min loop, it's awesome. But it beats your buoyancy control about the head with a lead pipe if you don't maintain min loop. Which is why you see so many people diving it with a weight strapped to the outside.

 

[tbone1004]

If sidemount is important to you, SF2 and Liberty are at opposite ends of the complicated spectrum. I went with SF2 due to it being one of the simplest (regarding electronics) eCCR designs.

The Liberty has the He sensors and associated backup PO2 calculations... don't remember how many O2 cells it has. But just seemed too complicated for my taste. There are a bunch of things I like about the liberty, but the electronics takes it off my list.

Diving the SF2 sidemount is an interesting challenge to get the hang of. Once you get to keeping it at min loop, it's awesome. But it beats your buoyancy control about the head with a lead pipe if you don't maintain min loop. Which is why you see so many people diving it with a weight strapped to the outside.

Liberty has redundant "sides" of electronics.
Each side has a brain box, 2x O2 sensors, 1x He sensor, 1x ambient pressure sensor, 1x solenoid. The first handset turned on becomes "master, the other is "slave".
One of the nicest things about the Liberty is that you can manually vote out cells which you can't do with Shearwater. Divers have died when voting logic has voted out the one "wrong" cell but that cell was the one that was correct.

 

[CptTightPants21]

Liberty has redundant "sides" of electronics.
Each side has a brain box, 2x O2 sensors, 1x He sensor, 1x ambient pressure sensor, 1x solenoid. The first handset turned on becomes "master, the other is "slave".
One of the nicest things about the Liberty is that you can manually vote out cells which you can't do with Shearwater. Divers have died when voting logic has voted out the one "wrong" cell but that cell was the one that was correct.

I am not a CCR diver nor do I have experience with the Liberty, but from my understanding the steps needed to confirm a voting logic failure would be the same no matter which unit you chose--or else how would you know which sensor to manually change with the Liberty? In either case, once you have identified the correct sensor you would be able to again correctly monitor PO2. I think I read that the voting logic failure stops the solenoid from firing correctly, but that O2 and Dil can still be manually adjusted.

 

[tbone1004]

I am not a CCR diver nor do I have experience with the Liberty, but from my understanding the steps needed to confirm a voting logic failure would be the same no matter which unit you chose--or else how would you know which sensor to manually change with the Liberty? In either case, once you have identified the correct sensor you would be able to again correctly monitor PO2. I think I read that the voting logic failure stops the solenoid from firing correctly, but that O2 and Dil can still be manually adjusted.

The traditional situation will always allow you to run the unit manually.
With Shearwater, if two cells fail similarly and there is one cell that is still good, then the unit will try to maintain ppO2 based on the cells that have failed. It still shows the ignored cell, but it fires the solenoid based off of the two, and it calculates deco based off of the two. You can kick it to the low ppO2 setpoint to run it manually, but your deco information will still be incorrect since the computer still thinks the pair are good.
With the Liberty you actually have the ability to tell it to ignore the bad cells and then it will calculate ppO2 and deco based off of the remaining cells. It will kick into automatic voting logic, but you have the ability to override it which is nice.
Is it a deal breaker? Absolutely not, but it is one thing that the Liberty can do that none of the DiveCAN units can do and for those that run their units off of the solenoid, it is something that should be considered.

 

[helodriver87]

The traditional situation will always allow you to run the unit manually.
With Shearwater, if two cells fail similarly and there is one cell that is still good, then the unit will try to maintain ppO2 based on the cells that have failed. It still shows the ignored cell, but it fires the solenoid based off of the two, and it calculates deco based off of the two. You can kick it to the low ppO2 setpoint to run it manually, but your deco information will still be incorrect since the computer still thinks the pair are good.
With the Liberty you actually have the ability to tell it to ignore the bad cells and then it will calculate ppO2 and deco based off of the remaining cells. It will kick into automatic voting logic, but you have the ability to override it which is nice.
Is it a deal breaker? Absolutely not, but it is one thing that the Liberty can do that none of the DiveCAN units can do and for those that run their units off of the solenoid, it is something that should be considered.

The classic example is two current limited cells that passed calibration but aren't quite able to reach setpoint high underwater. That could lead to a good cell being voted out and continous O2 addition leading to a hyperoxic loop. It should be apparent based on solenoid activity and buoyancy shifts, but the only real options are to reduce setpoint until the cells all behave appropriately after recovering the loop or bailout. You can't bring that good cell back. I don't know that being able to override the computer is a need to have, since you could get accurate deco information back by either lowering setpoint or bailing out and restoring good PO2 info, but it's an interesting option.

 

[kensuf]

I actually like axial scrubbers, but what do I know.