Question Sidemount rebreather as a first rebreather

[sea_ledford]

The only reason to get a SM CCR is if you are going to be taking it into places that need to side mounted. Otherwise the complications aren't worth the hassle.

I've only dove the SF2 sidemount, but between the back mount and sidemount version of the same machine, they are night and day difference. Backmount is pretty much throw it on and go (as much as any ccr is throw on and go at least, which is to say not at all), SM is a pain. First off you have to effectively have at least three bottles: O2, dil and bailout, but one SM position is occupied by the CCR. So you can take a small 2L O2 and tuck it away someplace, or put it in a sphere like the Liberty does. You can also use a "dilout" and combine dil and bailout, but you'll need an H valve, so your single point of failure is only the tank neck and not the rest of the valve and first stage as well. But you still have a single point of failure. Maintaining minimum loop volume is paramount to diving comfort and stability with a SM unit too. That was one of the slower things for me to "get" when I was first learning CCR. If I started with a SM unit, I probably would have decided ccrs suck and not pursued it further.

A back mount CCR providing feedback on the fact that you are not at min loop volume is like a 4 year old kid tapping your shoulder making slight suggestions that there might be something to fix. A sidemount at anything but min loop is like Hulk Hogan yelling in your face and body slamming you. My avatar is probably about dive 4 on the SF2 SM unit, I am NOT at min loop, so the but end is floating up.

The unit I bought was the BM, I've never bothered with getting the SM conversion kit.

 

[Rayk]

Wut?

Strawman and ad hominem much?

Relax guy, your combination of posts confused me and seemed somewhat at odds with one another.

I was saying same to you dude, just relax.

 

[Wibble]

It's about simplicity and learning.

Moving to a CCR is a MASSIVE change from open circuit. You need all your OC skills, then you learn new skills and need to forget some old skills. It takes hundreds of hours[1] to get competent on the unit and to suffer all the challenges CCR will bring.

OK, may be being a little over-dramatic here. The point is CCR requires a lot of effort to master and you need time to really sort things out. Everything from your attitude to building the unit (pedantic, thorough, not cutting corners); use of checklists; boat etiquette; in-water core skills (buoyancy, trim, finning -- vastly different from OC), stability in the water, ascents, bailing out, deco, climbing back on the boat; transporting it; post dive care; maintenance... But most of all quick and effective problem resolution, that 6th sense of knowing when it's not right.

There's no zero to hero "expert" CCR divers.

Backmount CCR is pretty sorted in terms of the popular units (JJ, Revo, AP, xCCR, Liberty, etc., etc.). Sidemount CCR isn't really sorted nor settled. Get one of the common backmount rebreathers and dive the backside out of it for a couple of years. Only then look at moving over to an esoteric sidemount specialist bit of kit.

There is a pretty clear consensus from those that dive CCR that you don't start on a sidemount rebreather. Obviously it's up to you and you may well be fine with it.

Knowing what I now know, I'm very happy with diving backmount CCR first, getting the experience sorted and only then applying that to other situations (overhead) and looking beyond my current unit.


[1] "hundreds of hours". Am talking of being really competent; a master of the rebreather. Most people can dive one straight after their MOD1 (initial) course. But things WILL go wrong and you must be prepared for them. The more complex the dive profiles, such as deep, long or overhead, means that you really need to be on top of your CCR diving skills and get into that zone where problems become minor challenges, not major issues as in your early dives.

 

[tbone1004]

@sea_ledford the Liberty uses 2x standard 2L bottles for O2 and dil. None of the units come standard with a sphere nor have they ever. You first saw the spheres on the bottom of a can with the LowRider but they become more common to see on the Sidekicks. The Liberty is far too long to even consider putting a sphere on the bottom.

Regarding your picture, if you talked with Forrest Wilson who helped develop the sidekick the pendulum motion during the breathing cycle was actually a benefit and you don't want to restrict the unit from bobbing up and down. Yours does have it fairly high and if you weren't at min-loop where it would fall back down towards the end of the inhale cycle I can certainly see where it would be uncomfortable. On my Kisskat I have a sphere on the bottom so the pendulum motion isn't there and it hangs pretty heavy so I have to be careful about how it attaches or it can be a bit of a pain. It does attach to a drop d-ring on my harness with identical attachment points as a LP85/121

 

[Underwater Tourist]

As you can see above, the writeup on what you asked from @rddvet is not so much about sidemount vs. backmount rebreathers but it's about the individual units and how they were designed. Most backmount units operate on the same fundamental design. Mouthpiece, exhale counterlung, canister in the middle, inhale counterlung. There are some exceptions like like the Revo/SF2, but most of them follow that same design paradigm and make them all functionally identical from a basic design perspective. Sure they're all slightly different with their own quirks but when we talk about the fundamental design of the unit a Meg, XCCR, Fathom, APD, Liberty, etc. they're all the same. When we talk about sidemount rebreathers though the only parallel that can be drawn between an SF2, Liberty, and Sidekick is that they are on the side of your body, they are all very fundamentally different rebreather designs so you can't simplify a backmount/sidemount comparison.

I see your point about sm rebreathers being conceptually different from each other. That said, if I were to construct a simplified hierarchy of rebreather designs (1=best): #1 is back mounted, #2 gemini/sw-style semi-sm rebreather #3 true sidemount rebreathers. Would it hold?

The only reason to get a SM CCR is if you are going to be taking it into places that need to side mounted. Otherwise the complications aren't worth the hassle.

I am looking into rb for cave diving, and while I know you can easily cave dive without ever needing a sm rebreather, I do think they offer more options especially in MX caves. As an example, during my cave training my instructor took me to Carwash and we went downstream following the right main line to Lower White room. Basically, its a narrowish zig-zag passage that goes up, down, left, right and it was a ton of fun to do in oc sm. No way you can do comfortably in doubles or a bm rb. Impossible.

 

[tbone1004]

I see your point about sm rebreathers being conceptually different from each other. That said, if I were to construct a simplified hierarchy of rebreather designs (1=best): #1 is back mounted, #2 gemini/sw-style semi-sm rebreather #3 true sidemount rebreathers. Would it hold?



I am looking into rb for cave diving, and while I know you can easily cave dive without ever needing a sm rebreather, I do think they offer more options especially in MX caves. As an example, during my cave training my instructor took me to Carwash and we went downstream following the right main line to Lower White room. Basically, its a narrowish zig-zag passage that goes up, down, left, right and it was a ton of fun to do in oc sm. No way you can do comfortably in doubles or a bm rb. Impossible.

There are far too many variables to paint that broad of a hierarchy. Every individual diver has a different weighting system, and even then those of us may have different weighting systems for each type of diving that we do.

Using your example, if you have a zig-zag passage with a lot of up and down motion without a lot of vertical space in the passage, especially in a shallow cave like Carwash one of the last things that I would want to do is be on a rebreather. It is utterly obnoxious to have rollercoaster type dive profiles and have to deal with a rebreather both from a buoyancy control perspective since your breathing is effectively useless as well as a ppO2 stability. One of the best ways to tell if someone is comfortable on a rebreather is to take them in a passage like that and see how they fare, but it's not something that I choose to do if open circuit is an option and the Lower White Room is not that far back, definitely not something I would choose to do in a rebreather.

Back to the original question, it all depends. When I am on a boat, I have a Meg rigged into a rack similar to the Fathom, Liberty Heavy, GUE JJ, etc. Full rig weight is comparable to a set of LP104's, so while it is over 100lbs, it's not egregiously heavy. With that rig I have all of the bottom bailout I need, suit/wing inflation, and O2 all in a self-contained package and the only things that I have on my sides are any decompression gases and/or whatever tools I need to complete the dives at hand, as anyone who knows me likes to joke that my gear is allergic to salt so if I'm on a boat I'm usually being paid to do it...
That rig however is NOT what I want to take into a cave because it is really big, has a huge drag profile when you're on a scooter which is a weird sensation, and while similar to @rddvet where I've been defaulting to doubles for the last 5 or so years instead of sidemount, the reality is that if I'm on a rebreather in a cave it's usually going somewhere fairly snug. The Kisskat is an improved Sidekick, so as the Kisskat is to the Sidekick, the Fathom Gemini is to the KISS Sidewinder, and that can be strapped to either a single tank, set of doubles, or as the left side sidemount bottle and offers me a tremendous amount of flexibility but it also is reasonable to get into/out of both in and out of the water, the Sidewinder is most definitely a PITA to get in/out of and is attached to the harness so you're not shedding it easily. The Kisskat allows me to dive anywhere I would in sidemount though I do have to be a bit careful with certain vertical passages where I usually just get off the loop if I'm going to be in there for longer than I can hold my breath, it's certainly an excellent tool for the job and there has yet to be a ccr released that really solves enough of the issues I have with the unit for me to bother switching.

It is extremely important to note that the vast majority of people that are weighing their opinions on rebreathers suffer from a need for confirmation bias to justify their investment but the age old saying of "you don't know what you don't know" is highly applicable. Any diver not trying to either sell you a unit or justify the unit they have will not be afraid to let you know the compromises that their unit has and the things they wish was different/is better on another unit. If you look at @grantctobin 's recent posts you will see a long list of complaints about his Sidewinder but also a list of things that he doesn't like about the Gemini he just bought. He has no skin in the game and has been around enough rebreathers to really know how to adequately critique them, the vast majority of even rebreather instructors do not know how to properly critique them and don't have enough experience on other units to know what is out there.

When you get to this level of equipment, it is all about being as educated as you can be and really knowing how to weigh the specific variables that you need in order to make the right decision. In this case, you're located in Canada but mention Mexico cave diving. That means you will most likely be flying and let me tell you, backmounted rebreathers are an utter PITA to fly with because they have so many parts and while it is certainly possible, they aren't light and they don't pack well. Nothing travels easier than the O2ptima CM and while the Choptima isn't a rebreather for me as a primary unit, you can't deny how flexible/adaptable/convenient the little thing is. Hell I think the whole unit fits inside just the canister of my Meg. I rarely have to fly with a unit, like has happened once in the last 5 years, so how well a unit flies is even on the list of variables of buying a unit for me but if you have to fly to get to your dive destinations a couple times of year it better be #2 on your list of variables behind "is it remotely safe to dive".

I would also ask you to really sit back and look at why you are wanting to go with a rebreather. If you aren't close to hitting the practical limits of open circuit diving then I would really suggest that you take a step back and put this on pause for a bit. Practical limits in OC sidemount are every dive being 2x al80 stages not including deco bottles. If you aren't at that point yet then you really aren't a point of justifying the hassle of rebreathers because you aren't being limited by the tools you have at hand.

 

[sea_ledford]

@sea_ledford the Liberty uses 2x standard 2L bottles for O2 and dil. None of the units come standard with a sphere nor have they ever. You first saw the spheres on the bottom of a can with the LowRider but they become more common to see on the Sidekicks. The Liberty is far too long to even consider putting a sphere on the bottom.

Regarding your picture, if you talked with Forrest Wilson who helped develop the sidekick the pendulum motion during the breathing cycle was actually a benefit and you don't want to restrict the unit from bobbing up and down. Yours does have it fairly high and if you weren't at min-loop where it would fall back down towards the end of the inhale cycle I can certainly see where it would be uncomfortable. On my Kisskat I have a sphere on the bottom so the pendulum motion isn't there and it hangs pretty heavy so I have to be careful about how it attaches or it can be a bit of a pain. It does attach to a drop d-ring on my harness with identical attachment points as a LP85/121

Thanks for the update on the Liberty, I was thinking it was the one that had a cage at the bottom for the O2, but now that you mention the Low Rider, that might be the one I am thinking about.

The pendulum with the exhale is what happens at min loop on the SF2, it just kinda bobs up and down. Once you get too much volume in there, it just stays up. And at 4.5 L volume, there is plenty more buoyancy to be had if a diver keeps adding gas. When the SF2 first came out in the US, I would see most of the sidemount divers with a 2-4 lb weight strapped on the lower section. That was just a cheat because they couldn't maintain min loop. That thing just beat me up for the first 6 dives or so until I figured it out. I don't have much good to say about my original SF2 instructor, but he did get that part right for me at least.

 

[Underwater Tourist]

@tbone1004 thank you for the write up, it was very helpful.

Like I mention in the very beginning, I am actually not planning to get a rb in the near-term future, I was just wondering how much of the advice to avoid sm rbs was driven by their designs vs. sw-specifc issues.

 

[lostsheep]

I was saying same to you dude, just relax.

I’ll elaborate on my initial comment.

I don’t think the CM has the same concerns as an actual sidemount rebreather. By that I mean the need to fine tune the position of the unit for WOB, the change in WOB due to changes in orientation, or the single dilout issue.

As I mentioned, the cm is the only CCR I’ve used. I am not qualified to properly compare and contrast nor am I advocating for the CM. My only knowledge of true SM rebreathers is from watching and talking to a SM Liberty buddy of mine. I’ve seen some of the struggles with orientation and positioning but have no personal experience.
I am very curious what your advisors think are the possible similarities that they use to discourage the cm as a first unit, but that is probably best left to another thread.

JIC anyone reading this thinks I’m loyal to my chop because it’s the only one I have, I am more than happy to to take donations towards another rebreather. A second rebreather would cost me half of everything I own so for now I dive what I got

 

[Rayk]

I’ll elaborate on my initial comment.

I don’t think the CM has the same concerns as an actual sidemount rebreather. By that I mean the need to fine tune the position of the unit for WOB, the change in WOB due to changes in orientation, or the single dilout issue.

As I mentioned, the cm is the only CCR I’ve used. I am not qualified to properly compare and contrast nor am I advocating for the CM. My only knowledge of true SM rebreathers is from watching and talking to a SM Liberty buddy of mine. I’ve seen some of the struggles with orientation and positioning but have no personal experience.
I am very curious what your advisors think are the possible similarities that they use to discourage the cm as a first unit, but that is probably best left to another thread.

JIC anyone reading this thinks I’m loyal to my chop because it’s the only one I have, I am more than happy to to take donations towards another rebreather. A second rebreather would cost me half of everything I own so for now I dive what I got

When it comes to decision, recommendations mostly towards getting BM with on board tanks rather than going other options as a first rebreather. It wasn’t anything unit specific against Choptima or any other.

I am not in the position to compare units which I haven’t have (enough) experience but I don’t believe it’s fair or logic comparing Choptima, Liberty SM to JJ or Tiburon etc. To me that’s comparing apples to oranges. Some may say all of them rebreathers and can be compared but it is same approach comparing crop duster to passenger jet. Yeah both are planes but...

I think one should first decide (at least that’s what I did) mCCR or eCCR. Than BM or not, than after if not BM, SM or CM. There are many posts about that process in the forum posted by much wiser people that I am when it comes to rebreathers.

It all boils down what do you want to do and how do you want to do it.