ScubaForce SF2 Rebreather Demo at Hathaway’s Pond

Hathaway's Pond

SF2 Rebreather Demo

I finally got the chance to do a nice demo on the ScubaForce SF2 rebreather with Alex Dulavitz of East Coast Divers.  My friend Luigi was also doing a demo on the unit as well.  Additionally, Aleksey joined us for a swim around on the pond on his Prism 2.

I will admit I have been intrigued by the unit for quite a while.  A backmounted counterlung unit providing good flood tolerance with a clean profile, simple setup, and good engineering.  At least on initial appearance these all appear to be true but maybe I bought into the marketing?

James Draker was nice enough to answer some technical questions and do very thorough breakdown and partial build of the unit while at Beneath the Sea last year for me.  I don’t really know him beyond admiring some of the beautiful pictures he has posted taken by Kirill Egorov, whom I also do not know.   While their group is diving a mix of different rebreathers it’s nice to know the SF2 is able to handle 6-8 hour runtimes at those depths.

My first impression of the unit was it didn’t look like someone’s half-finished science project. I admit to not being sold on the counterlung location up my ass but I also didn’t want to dismiss it on that without first doing a proper demo on the unit.

You can take what I say here with a grain of salt. I currently dive a rEvo mCCR with a little over 400 hours on mine. I’m obviously biased as it’s the only rebreather I’ve ever known. I still consider myself very green on rebreathers. This is my 3rd year on the rEvo just to give you some sort of a gauge of years vs. hours.   I obviously don’t have all the answers and nor do I claim to.

Keep It Simple Stupid or not..

I must poke a little fun here at the KISS booth at Beneath The Sea last year.  They didn’t seem to be very happy or willing to answer questions and seemed to ignore me when someone was actually present in the booth (I went by a few times and nobody was there).  First appearances are pretty important so I sort of wrote them off. Sorry KISS rebreathers, always next time.. 🙁  I guess I didn’t look like rebreather diver material or they were having an off day?

“Expedition” Diving in Hathaway’s Pond

For those that do not know Hathaway’s Pond.. It’s a very popular open water training site for checkout dives on Cape Cod.  It’s fresh water..Well “fresh enough” and it doesn’t get blown out like the ocean.  It’s probably one of the best places for confined water skills training outside of a pool in New England.  Admittedly I don’t go there very often since I prefer salt water but it’s a good place to kill a tank or two if the ocean is angry.

While the bottom is silty and muddy, if you stay off the bottom and aren’t accosted by hoards of open water students then the visibility can be decent 20-30ft+

Anyway..the point I was trying to make was Hathaway’s is pretty good place for a demo.  It’s better than sitting in a 10ft crowded and chlorinated pool.  A small open water class had just finished up as we were gearing up but other than that we had the entire place to ourselves.  I guess that’s the nice thing about the fall on Cape Cod.  Not too many tourists.

Flood Tolerance: Do I need this?

I’ve never really flooded my rEvo but it’s always pretty wet inside after 2+ hour dives. This is something that always concerned me compared to other units but it’s never caused issues with any of my cell readings. If I have the opportunity between dives I ring out my shammys and clean any moisture/condensation out of the unit as best I can. If you’re planning 6-8 hour dives this may be a problem. I truthfully don’t know the answer to this as my longest dive-to-date on my rEvo has only been been a little over 4 hours.

I’m starting to gradually do longer dives and think about the future. I really want my next unit to have some sort of flood tolerance. True it’s never been an issue on my rEvo but if I ever have the opportunity to be 4-5+ hours in the back of a cave and/or facing 4-5+ hours of decompression in the ocean I’m starting to think that it would be really nice to be able to de-water the loop and recover from a loss of the DSV.

Let me correctly myself slightly, the one and only time I did “flood” it was while climbing up a boat ladder due to poor DSV management in heavy seas at the end of the day so I didn’t lose any diving. This was when I was at something like 20 hours on the unit. The unit was probably still dive-able but it was end of the day so I didn’t try finding out and didn’t want to test that theory.

SF2 First Impressions

There are a lot of things that drove me to look at the SF2.  First, I can actually replace the counterlung on the SF2 myself.  What a novel concept!  Even more exciting, I can actually buy a brand new counterlung from the factory and keep one on hand as a backup.

The valves were much easier to reach valves (for me). I have short t-rex hands and with thick undergarments I always had a tiny issue reaching my rEvo valves due to how far off my back they are. Don’t get me wrong I can do it but it never felt “clean” to me.   I know this is not unique to the SF2 but as with other “can” units that I’ve tried like the Prism 2 and JJ they are literally right there. I can just simply reach back without any sort of contortion needed.

I felt the unit trimmed out very nicely. A lot of rEvo divers need to resort to putting 8lbs of weight on the top of the unit and switching to neutral fins to get a rEvo to trim out nicely else you risk looking like a sea horse underwater.  I didn’t have to do anything special, it was just there.

To be honest the work-of-breathing (WOB) as fine. No better or no worse than the rEvo and I was diving air diluent.  Granted I was only at 50ft or so for part of the dive but I had no issues with work of breathing.    People joke but I haven’t done air diluent since March. There is always a bit off Helium in there. That’s one way I found to fix poor (or perceived poor) WOB.

We only did an hour runtime but it allowed me to try the unit in a variety of different positions, get used to the MAVs and do a bunch of boom and valve drills myself.  I thought the MAV locations were nice and easy to reach.  I’m on a mCCR now so I get a nice and easy feeling when I can simply reach my gas block on my rEvo and add O2 and Diluent.

I ran the SF2 with the solenoid set to .7 (as a parachute) and manually kept my setpoint at ~1.0-1.2 with the O2 MAV.  We were only in 20-40ft of water most of the time so obviously deco obligations were not really a concern.

The other thing I really liked was that I thought the cells stayed pretty dry.   To be honest It’s never been an issue for me on my rEvo but I’ve always been a little uneasy with the amount of moisture and condensation on my cell tray. It’s always pretty wet inside after 2+ hour dives. This is something that always concerned me compared to other units but it’s never caused issues with any of my cell readings. If I have the opportunity between dives I ring out my shammys and clean any moisture/condensation out of the unit as best I can.

rEvo Exodus?

The rEvo is like a first love. It’s all I’ve known for rebreathers so there is bias there. I have 400 hours on my mine and I am still pretty new on rebreathers. There are things I really like about it and things I hate, really hate.

Things I like..Efficiency on sorb, complete set of redundant electronics, slim profile, easy of travel, simple build, less failure points, very customize-able.

Things I hate.. lack of flood tolerance, lack of some user replaceable parts, heavy and super negative, cells get wet easily, shitty revoDreams for secondary monitoring.


I really enjoyed demoing the SF2.  It seems like a fantastic and well engineered unit but I realize an hour underwater on one is really not enough to have an authoritative opinion or gauge all it’s strengths and weaknesses.  Still…I was very impressed and happy with my dive on one and it’s definitely made it on the short list in my search for the next rebreather that I might purchase.

For the record I have no plans to sell or stop diving my rEvo. It’s a fantastic machine and I am grateful of all the fun diving it has provided me. I am however not opposed to adding an SF2 to the shelve along with my rEvo.  I believe they can co-exist in my dive locker (a basement really..) and hopefully play nicely together.

I’m planning on buying something new or used in the next 6-7 months depending what I find.  I don’t know exactly what unit it it will be. Maybe another rEvo or a JJ but it’s looking like an SF2 is a distinct possibility.

Like with everything there doesn’t seem to be a one-size-fits-all approach to rebreathers. You have people with very strong opinions who are convinced that the glorified humidifier on their back that they just spend $10K on is the best unit on the market.

Hathaway's Pond

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