SF2 or REvo rebreathers

[The Chairman]

What does the CANbus do with your set point if the handset controller croaks? Including what does it do when you ascend?

It copies wherever you were at. It won't change on ascent.

 

[joshk]

What does the CANbus do with your set point if the handset controller croaks? Including what does it do when you ascend?

Keep in mind I haven't tried disconnecting the controller underwater and doing an ascent. It might switch to low setpoint.

 

[The Chairman]

Keep in mind I haven't tried disconnecting the controller underwater and doing an ascent. My understanding is it switches to your low setpoint and maintains that.

I had the Shearwater battery die, and it kept the same as I was.

 

[kensuf]

What does the CANbus do with your set point if the handset controller croaks? Including what does it do when you ascend?

It tries to maintain the last setpoint you had programmed.

 

[mmadiver]

I'm looking to get into the rebreather world and have the hard questions to answer. Which unit do I select? I have narrow the field down to two rebreather units, the SF2 and rEvo. I would like to ask the community their thoughts (constructive please) on the both units.

I do realize that both units are very good and will do their jobs is you take care of them and dive correctly. What I'm looking for in the discussion is the finer details and longer term considerations.

Thanks all,

Hi Johnny,

I've been diving a Revo for three years and recommend it. When I was looking to buy a new unit I was torn between the JJ and Revo. I have been diving CCRs since 2007, albeit all military CCRs, but I had an idea of what I was looking for... I wanted a CCR that was compatible with true expedition diving. The term "expedition" gets thrown around a lot in the technical diving community and depending on who you ask you'll get a different definition; for me I needed a rig that was compatible with conducting dives away from any type of support. I need a CCR that can fly with me around the world, go to sea for days/weeks at time, and work when its time to get in the water. To put more simply, my primary selection criteria is dependability and by extension a system designed with minimal failure points. When I'm spending thousands of dollars to go somewhere to dive or have chartered a boat for a multday sail the CCR needs to work when I get there (or at least be user fixable).

That level of dependability is a unique "need" that I have an may not be applicable to your type of diving. For example, cave divers may have different priorities as many of them are essentially diving in their back yard, are in close proximity to support functions, and are able to walk into the water.

My other criteria for CCR selection are:
- WOB: it has to be good. CO2 retention is the single greatest risk facing a well trained, alert, and competent CCR diver.
- Redundant Systems: See dependability above. Split scrubber and 5 x cells (2 x revo dreams) are great things to have on a boat when you're days away from shore.
- Streamlined: For CO2 considerations, and squeezing through wrecks.
- Shearwater Electronics: Simply the best
- Bouyancy characteristics: 90% of my diving is drysuit, revo's are pretty negative and well suited for drysuit diving.
- Simple Buildup/Breakdown: Nobody wants to spend all day dicking around with gear, especially on a pitching boat.

Flood tolerance is at the very bottom of my criteria. In 10 years of CCR diving I've never had a flood. It's not even a consideration for me given that I'm wreck diving; I'll just bailout and surface. I also see floods as "operator error" which are most likely to happen at the surface when the DSV is out of your mouth. So again, not really a consideration especially given how tight the Revo's loop is - mine can hold a negative for days...

Hope that provides some food for thought. Good luck on your selection and welcome to CCR's.

Also, it's worth mentioning that in three years of diving my Revo it has never malfunctioned, not once. I have never missed a dive due to the revo.

 

[NAND]

They have (or support) dual, redundant controllers?

Stuart, sry for late response, was travelling for some time.

I think the CCR concepts available on the market are quite different. Speaking about the rEvo, the setpoint controller can be seen as an 'add-on', not needed for permanent operation but nice to have.

The way I normally dive my unit is almost purely manual. Meaning you just set your PO2 manually and dive it, using the controller as a pure failsave in case you are distracted. Concerning your question: the unit comes equipped with at least one fully independant (no wired connections) PO2 monitor which supplies a small LED-HUD. REvo calls this 'rEvo-dream'. Most time of the dive, I depend on this HUD while being busy doing other things.

However, on my unit are two of them, called the rEvo expedition. Aditionally, the Shearwater monitors my PO2 and uses it as divecomputer and setpoint controller. Meaning, my PO2 drops below Setpoint, it will fire the solenoid.

The advantage of this particular Petrel2-firmware is the 'RMS', actively monitoring the scrubber. But thats another story...

So- here you go. In standard config there is one backup to the main PO2 monitor, setpoint is single controller. (Makes sense for me in terms of not connecting 2 independant systems to one solenoid making them prone to failure).

In Exp config there is double backup to PO2 monitoring, again 3 units (2 Dream, one Petrel) fully insulated.

You may however (like some people do) decide to eg. use a Nerd and a Petrel, depending on your out-of-pocket expenses

In real life I am more than happy with the setup I have- when I was concentrating on a photo under water and the solenoid fired (though its a very silent 'pfffft-click'-noise and I was relatively new on the unit) it sometimes really woke me up... Happening very rarely but I remember in the past I still made use of the controller casually...

 

[Capt Tom McCarthy]

I want to learn this one as well


It does, but only one solenoid. However, if you consider the diver a 'controller', then yes. The main Shearwater is the controller and monitor. Should it fail, the CAN Bus takes over both jobs, though you won't see the status of the cells. Add a PDC to the Fischer cable and now you have triple backup. However, should the CAN Bus fail, then your main Shearwater can't control it, but the diver can. I haven't been told if the primary Shearwater would still be displaying cell info. Ergo, I have another Shearwater on the Fischer just to be sure. Perhaps @Capt Tom McCarthy can weigh in on this.

The controller sends a begin dive and end dive message to the SOLO board. If the controller is cut from the system before the end dive message is received, the internal board will maintain a setpoint of 0.7, assuming you still have a functional 9v inside the head. This only works underwater and you can't test the failure mode on the surface.

At this point you can still monitor your PPO2 with a secondary fischer based computer while flying the unit manually at a higher PPO2 if you desire. You wouldn't really want the last setpoint being the default failure mode as you may be at a shallow depth where a certain higher PPO2 is unobtainable or difficult to maintain. This would lead to the O2 firing non-stop.

 

[Capt Tom McCarthy]

I think they're both really great units. It's why I chose to dive them and eventually teach them.
I find that the people who hate on rEvo usually have a personal problem with them or an instructor. In many cases they have legitimate points for their anger and I wont try to belittle their experiences.

As a unit I think the rEvo is fantastic. I like the triple electronics but i've never claimed that they are required to dive a rebreather safely. They are, however, a really nice thing to have on an offshore charter or a remote dive trip where if one system fails, you move a few molex connectors and you still have two redundant monitoring systems left. I like the low profile of a revo in backmount, the geometry of the dual scrubbers makes it lower than any single scrubber system can obtain in backmount.

The SF2 is really nice as well. The design is unique. The carbon fiber is great for travel. The shearwater controller is, in my opinion, the gold standard. The build up/ break down is simple and easy. It also has the added benefit of being sidemountable.

I think in backmount only, there are a few things that I like about the rEvo that give it an edge over the SF2 but once I factor in the sidemount conversion then I think it edges out over the rEvo (for what I do personally). The price tag on the SF2 does level that a bit so at the end of the day it's a really hard choice between the two. One that I feel should be made by looking at the instructor available and if you have any friends/acquaintances who you can bounce things off of (or an instructor near by who you can harass and buy beer for indefinitely). I love them both and I wouldn't be the least bit sad if I could only ever dive one of them.

 

[stuartv]

Stuart, sry for late response, was travelling for some time..

Gotcha. Thank you for the thoughtful and detailed response!

 

[Doc Ben]

Hi Johnny,

I've been diving a Revo for three years and recommend it. When I was looking to buy a new unit I was torn between the JJ and Revo. I have been diving CCRs since 2007, albeit all military CCRs, but I had an idea of what I was looking for... I wanted a CCR that was compatible with true expedition diving. The term "expedition" gets thrown around a lot in the technical diving community and depending on who you ask you'll get a different definition; for me I needed a rig that was compatible with conducting dives away from any type of support. I need a CCR that can fly with me around the world, go to sea for days/weeks at time, and work when its time to get in the water. To put more simply, my primary selection criteria is dependability and by extension a system designed with minimal failure points. When I'm spending thousands of dollars to go somewhere to dive or have chartered a boat for a multday sail the CCR needs to work when I get there (or at least be user fixable).

That level of dependability is a unique "need" that I have an may not be applicable to your type of diving. For example, cave divers may have different priorities as many of them are essentially diving in their back yard, are in close proximity to support functions, and are able to walk into the water.

My other criteria for CCR selection are:
- WOB: it has to be good. CO2 retention is the single greatest risk facing a well trained, alert, and competent CCR diver.
- Redundant Systems: See dependability above. Split scrubber and 5 x cells (2 x revo dreams) are great things to have on a boat when you're days away from shore.
- Streamlined: For CO2 considerations, and squeezing through wrecks.
- Shearwater Electronics: Simply the best
- Bouyancy characteristics: 90% of my diving is drysuit, revo's are pretty negative and well suited for drysuit diving.
- Simple Buildup/Breakdown: Nobody wants to spend all day dicking around with gear, especially on a pitching boat.

Flood tolerance is at the very bottom of my criteria. In 10 years of CCR diving I've never had a flood. It's not even a consideration for me given that I'm wreck diving; I'll just bailout and surface. I also see floods as "operator error" which are most likely to happen at the surface when the DSV is out of your mouth. So again, not really a consideration especially given how tight the Revo's loop is - mine can hold a negative for days...

Hope that provides some food for thought. Good luck on your selection and welcome to CCR's.

Also, it's worth mentioning that in three years of diving my Revo it has never malfunctioned, not once. I have never missed a dive due to the revo.

So given what you say above, compare Revo to the Optima. Have you any time on the Optima?