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Probably stupid question

Discussion in 'Basic Scuba Discussions' started by Crackerbacks, Jul 29, 2020.

  1. Crackerbacks

    Crackerbacks Angel Fish

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    Ok so this is probably a stupid question but I have to ask.....

    I am looking at a new wing and all of the different lift weights and I got me thinking. If one is weighted properly why would you need so much lift in some situations and only 18-20 pounds is other situations. I know the answer will be tech diving but again I would think if one is weighted properly it should not matter?
     
  2. Bigbella

    Bigbella ScubaBoard Supporter ScubaBoard Supporter

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    For example, should you be carrying other weighty equipment -- say, a full sized camera housing -- or collecting, without a dedicated lift bag, it pays to have some liberal lifting capacity in a BC, beyond that of, simply, your ballast.

    Years ago, we were moving and arranging oysters in book nets, in an estuary setting; and it paid to have 30 pounds of lift, when futzing with those; or when lift bags were occupied . . .
     
  3. swimlikethefish

    swimlikethefish Divemaster

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    Example:

    If all of your gear including neoprene is 14 lbs buoyant, that means you need 14 lbs of counterweight. Now if you descend to depth then some of your gear might lose buoyancy (think neoprene.) Now you would be 28 lbs overweight. So you would need a 28 lb wing to compensate.

    Just a quick example, those numbers are fictional. But you get the idea.

    Could also apply to a drysuit. If the suit were to flood you just lost some of your positive buoyancy. Especially with a set of steel tanks.
     
    MightyDuck and Lostdiver71 like this.
  4. Subcooled

    Subcooled Assistant Instructor

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    A wing/BCD provides adjustable buoyancy (but it is not intended as an elevator, or lift). During your dive you will discard a number of pounds of air. Because of this you will become more buoyant as the dive progresses. Hence, you must carry extra lead and extra air volume in your wing to compensate. As you exhale the air and become more buoyant you also vent the wing to compensate. This is relevant in all sorts of diving where lots of gas is carried (also a 4 hour long recreational dive).

    Equipment weight, as told in a previous post, is a good reason.

    Another reason is drysuit diving. A drysuit is VERY buoyant and will require lots of lead to sink (gold would be better as it is more dense but it would still weigh the same). If something happened to the suit - the mythical catastrophic loss of buoyancy - one might need 9 kg or 20 pounds of extra lift. Adding the weight of air/gas to this, you will end up with 28 pounds of lift or more. I have 38. It is probably too much as I did open the drysuit zipper while submerged in a pool (mentor asking) and nothing bad happened.
     
  5. RyanT

    RyanT ScubaBoard Supporter ScubaBoard Supporter

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    I'll add that having some extra lift on the surface can be useful. It can be used to assist another diver who is struggling or just to hold you head a little higher above the surface.
     
    Subcooled likes this.
  6. jborg

    jborg Lurker ScubaBoard Sponsor

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    A lot of your bouyancy is in your person and your exposure suit, while most of the weight (excepting weight belt) will be in the rig. It might be nice to be able to take off your rig at the surface and have it float, so the wing needs to be sized accordingly.
     
  7. Subcooled

    Subcooled Assistant Instructor

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    My buoyancy is about 4.4 pounds.
    The rest (at least five times more) comes from the diving suit.
     
  8. halocline

    halocline Solo Diver

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    It's not a stupid question. The answer is that you need different amounts of lift depending on the thickness of your wetsuit. Basically you need lift to compensate for changes in your buoyancy throughout the dive. The two main things that cause buoyancy changes are wetsuit compression and gas usage. Unless you are diving huge steel tanks, the weight change of the gas will always be around 5-7lbs throughout a single tank dive, not much of a range. But a 3 mil suit might only lose 5-8 lbs of buoyancy while a 7 mil farmer john could lose 20 lbs or more, and your wing needs to compensate for that.
     
    BrackaFish and Subcooled like this.
  9. Bigbella

    Bigbella ScubaBoard Supporter ScubaBoard Supporter

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    Intended or not, BCs have been used for lifting, ever since those horse collar days; and was one of the primary reasons that I purchased one, instead of simply remaining with a hard backpack and straps, that I had had for years; and suffered few buoyancy issues which weren't corrected by actually swimming, one direction or another, in the water column.

    That added float aided in work underwater, along with the use of lift bags . . .
     
  10. Crackerbacks

    Crackerbacks Angel Fish

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    Thanks for the insight guys!
     

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