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Weight checks and RBs?

Discussion in 'Rebreather Diving' started by rjack321, Mar 3, 2008.

  1. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
    Honest question here...
    How do RB divers do a weight check? And the corallary... In sizing a wing do you account for the lack of bouyancy due to a fully flooded loop? I'm guessing you would just be calculated this based on loop/canister size etc.??
  2. ScubaDadMiami

    ScubaDadMiami CCR Instructor

    There are different philosophies and equipment configurations for weighting. Definitely, one must have sufficient lift in the wing and equipment to compensate for a flooded loop. The manufacturer can often provide this information or at least the volume of the canister and loop.

    One must also consider what will happen when draining gas from the tanks and weight accordingly. Some add weight to the offboard tanks rather than carrying it on the rig. Others carry the weight on the rig. Things like this must be agreed upon by team members since it might be necessary to swap tanks in an out of gas situation.

    All of this should be covered in your training. So, follow the advice of your instructor about things like this (not statements like mine or others over the Internet).
  3. rjack321

    rjack321 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Port Orchard, WA
    Different philosphies? Can someone elaborate on that?

    I'm assuming you need enough lead to stay down with nearly empty bailout cylinders and nearly empty dil and O2 cylinders. And enough lift to support a flooded loop and basically full bailout cylinders.

    Do people consider ditching or other options? I only ask because it seems kinda hard to try out the various light and heavy conditions, and changing exposure suits etc, unlike on OC.
  4. scubanimal

    scubanimal Instructor, Scuba

    # of Dives: 500 - 999
    Location: San Diego
    Most RB divers are diving a bit more than just recreational, as such their specific mission (dive) needs vary depending on the dive. For instance, a team of divers going deep in to caves could have a very different set of requirements than say a buddy pair going to do a photo shoot with dolphins. Add to that that rebreathers are still relatively new in the mainstream and the various agencies have not yet developed guidelines that have enough data to support a particular philosophy (general guidelines). Each of the agencies right now that support RB training have an independant root of base knowledge developed from ad-hoc experience in their particular diving interest. Now I don't mean to say this is not thought out, only to indicate that there just is really not a "proven" this is how you should setup and dive an RB. Add to that the individual that is currently your 'typical' RB diver. In general they are your above-average skill level, generally well educated, a certain level of affluence (RBs cost a lot) and most of these folks are risk takers. Maybe not crazy type, but measured risks. All RB divers right now are pushing the state of the Art and are pioneering the technology. Depending on what numbers you want to believe, there are only about 10,000 RBs being dived on any kind of regular basis across this planet. These forums and the training agencies are pretty much the only link between these divers. So not a lot of cross training and subsequent cross education is happening yet. Most of the manufacturers are very small garage type operations that can not afford to do the type of testing required to provide guidelines from an implicit set of data. And finally the RBs on the market right now vary significantly in their bouyancy characteristics so one set of "rules" is probably not the best for every type of unit.

    So as ScubaMiamiDad said, there are diffierent methods being used and the training an individual takes covers the various issues. A RB user must take a course for each type of RB he/she wants to dive.
  5. silent running

    silent running Manta Ray

    # of Dives: 1,000 - 2,499
    Location: Brooklyn, N.Y. U.S.A.

    Good question, especially the part about a flooded loop.

    This is my understanding, such as it is, never tested it out and I hope I never have to...

    Given that a CCR diver should always maintain minimal loop volume and that nobody dives with a full 6-8ltrs of gas in their loop and that once your loop has fully, catastrophically flooded it will be full of water and in equalibrium with the water around it-you should be able to recover with a wing who's capacity is a little more than the dry weight of your unit minus cylinders, plus your lead, plus the in-water weight of the cylinders you are carrying. All that being said, you will certainly have a tough time getting up the boat ladder with a flooded loop, no matter how big your wing is.

    I need less than 5lbs for my Prism with a 3mm suit and an aly 40cuft BO cylinder, so I have a 36lb Zeagle wing. If I were regularly diving with 2 or more bigger BO stages, I would get a bigger wing. FWIW, I needed much more weight when diving an SCR Drager as it was a constant mass flow gas addition system and I need enough weight to get down with the loop close to max volume, another disadvantage of CMF SCRs that I hadn't thought of before... -Andy
  6. JeffG

    JeffG Solo Diver

    # of Dives: 500 - 999
    Location: Edmonton, Alberta
    After you have finished patting yourself on the back and polishing your pedestal. Diving a RB doesn't change physics.

    Its not near as technical as you would like us to believe.

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