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Thread: All about the compromises

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    RBW Member broncobowsher is on a distinguished road broncobowsher is on a distinguished road broncobowsher's Avatar
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    All about the compromises

    So I am confronted with a dozen different brands/models of rebreathers on the market. To some extent they are all the same, but there are still differences. The manufacturers have made decisions that are a compromise. They make a choice about how it is designed and this gets better but that gets worse.


    Without getting into a name slinging competition I'm trying to figure what set of compromises would be best for each person's taste. Things like scrubbers can be had radial or axial flow. Sometimes the builders will even have one as an option over the other. What do you gain/loose over one design over the other?


    How about counterlung placement? what do you gain/loose with front/shoulder/back/butt mounted counterlungs?


    There are a lot of things that can go into this. Gas injection placement. before/after scrubber. What are the gains/losses for each way?


    For every advantage there is going to be some sort of disadvantage, or else no one would do it the other way.


    By no means am I an expert. I tend to usually sit back and be a fly on the wall and just read what others are putting out. But after a long time of reading I still have not found a concise description of what options are good for. There are little bits here and there, but not gathered into a single spot. I'm sure I have not listed all the things that separate one option from another, so feel free to add. Things like a molex connector and a coax connector on cells. Why do some go one way and others the other? Just thought of that.


    For the most part this discussion should be based on generalities, maybe with a reference to how one brand does it. Not after a model by model comparison, but a feature by feature comparison. So educate me (and everyone else who knows a bit about rebreathers but knows that there is a lot more to learn).

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    RBW Member EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD's Avatar
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    Re: All about the compromises

    If someone can answer your post you n 20 sentences suitable for everyone else he would be able to build the perfect ccr.

    I think everything comes down to personal preference and for what kind of dives you want to use it




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    Re: All about the compromises

    As someone who dives multiple units with different configurations, I came to the conclusion that there is no such thing as a perfect unit. I agree with Engelen that ultimately it comes down to personal choices and what you are willing to compromise with. For a new person getting into CCR diving, my advice is to just take a class without buying a unit. See if you can rent the unit for class and after the class, you will already have a better IDEA what you are looking for. If still unsure, take a cross over class on another unit of interest. Again, see if you can rent.

    Another personal experience has been that as an experienced CCR diver simply looking at another unit's feature that is new to me, I do not have the ability to know whether I like that feature or not. There have been multiple times when what I thought I may not like on a new unit I liked and vice versa.

    Best to keep an open mind.

    Claudia

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    Re: All about the compromises

    Are you looking for answers or questions? In other words, are you trying to compile a list of differences and the compromises they entail? That's how your post read to me.

    You got a good start with

    CL placement - back, front, or TOS?

    Scrubber - axial or radial?

    Sensor connection - coax, molex, mini plug, or proprietary?

    O2 injection - before or after scrubber?

    How about some more......

    Scrubber number - single or split?

    Cell placement in loop - inhale or exhale?

    And of course the biggie ....
    Electronics - mCCR, eCCR, or hCCR?

    There are dozens more design decisions made. I'd like to open the discussion up for additions.



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    RBW Member broncobowsher is on a distinguished road broncobowsher is on a distinguished road broncobowsher's Avatar
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    Re: All about the compromises

    Quote Originally Posted by kwinter  View Original Post
    Are you looking for answers or questions? In other words, are you trying to compile a list of differences and the compromises they entail? That's how your post read to me.

    You got a good start with

    CL placement - back, front, or TOS?

    Scrubber - axial or radial?

    Sensor connection - coax, molex, mini plug, or proprietary?

    O2 injection - before or after scrubber?

    How about some more......

    Scrubber number - single or split?

    Cell placement in loop - inhale or exhale?

    And of course the biggie ....
    Electronics - mCCR, eCCR, or hCCR?

    There are dozens more design decisions made. I'd like to open the discussion up for additions.



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    I think you are getting what I am asking. I know of the physical differences (you just really cleaned up the questions and added more good ones).


    But what are the functional advantages/disadvantages to each? If it were car shopping it would be something like the bigger engine option has better acceleration but worse fuel economy. The advantage and disadvantage of the big engine over the smaller one.


    Not asking what is better or worse, that should get into the personal preferences based on the advantages/disadvantages. For one person the fuel economy may be more important while I may want the acceleration and willing to accept less fuel economy. Both options are valid, but different based on each persons personal priorities.

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    Re: All about the compromises

    Quote Originally Posted by broncobowsher  View Original Post
    I think you are getting what I am asking. I know of the physical differences (you just really cleaned up the questions and added more good ones).


    But what are the functional advantages/disadvantages to each? If it were car shopping it would be something like the bigger engine option has better acceleration but worse fuel economy. The advantage and disadvantage of the big engine over the smaller one.


    Not asking what is better or worse, that should get into the personal preferences based on the advantages/disadvantages. For one person the fuel economy may be more important while I may want the acceleration and willing to accept less fuel economy. Both options are valid, but different based on each persons personal priorities.
    I think you are almost there- the bridge you need to gap is not Functional, all the major units "work" in a Life maintaining while diving scenario but are emotional, philosophical, practical and compromises you (the diver) has to choose.

    FMCL vs BMCL- Both work, one leaves clear chest space, one makes unit on back slimmer, technically the WOB nod breathing sensation differs (one is above, the other is below your lung centroid) does it make any real world difference? That's up to you I'm afraid.... but FWIW most units are now offering to BMCL and those who change are generally satisfied- why? Maybe just because you gain space around you.

    THe other issues are largely the same- axial vs radial- no real world difference except in extremis, MCCR vs ECCR- no real world difference except in philosophy.

    Arguably whatever you choose (if your first rebreather) will be wrong.

    The general advice has always been-
    1. Choose what your buddies have. (For commonality)
    2. Choose something made locally for servicing/spares support.
    3. Choose the market leaders because they are the most tested (by divers in real world)

    If you go through the parameters available and actually choose your preference you may well end up with a unit that does not exist, then you'll either be permanently disappointed or have to build your own unit.

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    RBW Member JohnnyC is an unknown quantity at this point JohnnyC's Avatar
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    Re: All about the compromises

    Much of it is as much personal preference as anything.

    I went from a Meg, to a Pelagian, to now an SF2 along with my Pelagian, which will eventually have the O2 MAV swapped for a needle valve and run as a hybrid.

    I prioritized streamlined and free chest when I went to the Pelagian with BMCL's, and the needle valve because I liked the ease of control I had. Of course this came with a swap from an 8lb radial scrubber to an axial design in the Pelagian, for me it has yet to make a difference.

    From there I decided I liked the streamlined configuration of the SF2, but wasn't satisfied with purely manual control. Now, I will have the eCCR backing up the needle valve, as well as a more protected counterlung, and staying with the simple design that I liked having with the Pelagian.

    Sure there are compromises in some respects, but I don't necessarily view them as such. My Meg was a great unit, I just wanted something different, and in this case it was an entirely personal opinion, and I don't really feel compromises were made, simply a change in overall philosophy.

    Trying to put objective comparisons on most of this stuff is hard as each has equal advantages and disadvantages, depending on your perspective, or the type of diving you'll be doing. Most is entirely subjective. Which coincidentally is why we have so many options on the market.

    I have a friend who dives a Poseidon because he's a pilot by profession and is comfortable with the level of automation in the units. I am not, I feel there's a large difference between the amount of testing and redundancy involved in avionics in comparison to a rebreather. He likes the idea that he can travel with just his battery and rent any Poseidon unit and dive as he pleases. I am less comfortable with the idea of diving a unit I am not personally responsible for the overall health and maintenance of the unit. Again, we differ in our opinions about what is important to us individually, but we still manage to dive our units and be quite happy with them.
    Last edited by JohnnyC; 30th May 2017 at 19:38.

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    RBW Member EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD is a jewel in the rough EngelenD's Avatar
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    Re: All about the compromises

    For me the main reasons to go for rEvo where:
    -I visited the factory and was very pleased by the way the make, test and follow up their units and keep improving.
    -lots of people around me diving the unit and besides the fact they where al happy with it this would make the learning much easier when you have experienced people to count on !
    -easy to buy spare parts
    -easy to build

    Have fun searching and diving when you get one !
    David


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    Re: All about the compromises

    I would add a question to your list which I think you have missed which is also the most important.

    - Is it reliable?

    A good way to find out an unbiased view is to ask a local skipper that takes a lot of CCR guys, simply ask when it is time to jump who is in the water and who is left on the boat screwing around with there unit?

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    Re: All about the compromises

    Quote Originally Posted by EngelenD  View Original Post
    For me the main reasons to go for rEvo where:
    -I visited the factory and was very pleased by the way the make, test and follow up their units and keep improving.
    -lots of people around me diving the unit and besides the fact they where al happy with it this would make the learning much easier when you have experienced people to count on !
    -easy to buy spare parts
    -easy to build

    Have fun searching and diving when you get one !
    David


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    Try buying a counter lung and see how easy that is since they will not sell to the end user

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