Interesting that chest mounted units are also mentioned, from my reading, my understanding is that there arent major differences between chest vs back mounted units. Either your rb will be easier on the inhale or on the exhale, thats about it
Dont think there is any debate on sm vs doubles, Bogaerts has proven pretty convincingly that it absolutely doesn't matter and you can start with either one. But when it comes to sm vs backmounted rebreathers, there are objective tradeoffs, which I am trying to understand more
"True sm" rebreathers had major wob issues because the counterlung was located very far away. The concept behind sw solved some of those issues and provided better wob relative to "true" sm rebreathers. Is that correct? Which means that the hate for the SW mainly comes from quality woes, as opposed to the concept as a whole?
It's unfortunately not that simple. We are talking about fundamental design differences in the rebreathers and it doesn't have much to do with where they are located on your body.
The RB-80 evolved into the SF2 which has the bellows on the bottom. It is there whether you are diving a backmount unit or a sidemount unit and that makes the WoB of that unit very susceptible to your trim. It does the same thing whether it is on your side or on your back though with the sidemount unit it is also suspectible to roll which we tend not to worry too much about.
Sidekick is similar with regards to WoB but the WoB on these units when they are fit properly to the diver is perfectly fine so I would not say they have "major WoB issues" just that they are less forgiving to improper fit or major deviations in pitch and roll.
The Liberty puts the counterlungs right under your armpit so it is not really susceptible to big swings in WoB with trim, no worse than a backmount unit, but is still susceptible to roll.
One useful piece of feedback that you get from a backmount unit is the "gurgle" where liquid on the exhale side will back up against the mushroom valve and tell you if you are getting too much spit/water/etc in that loop. None of the chestmount or sidemount units will give you that type of feedback because the mouthpiece is the highest point of the loop. The Sidewinder can give you that feedback if it is configured properly which is helpful, granted if you have the Poseidon BOV it won't but that's the BOV itself, does it on the Se7en and on my Meg.
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.
@Cheizz Part of why you are seeing so much of this discussion is because of how relatively easy the Sidewinder is to start into the CCR world, particularly if you are already diving sidemount so a ton of units are being promoted and sold to divers that really have no business being on rebreather to begin with, heaven forbid being on a unit with design compromises to facilitate types of cave diving that maybe 3 dozen people in the world are actually doing.
