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Why do I sink when I turn upside-down?

Discussion in 'Basic Scuba Discussions' started by CaveSloth, Oct 31, 2019.

  1. CaveSloth

    CaveSloth Barracuda

    # of Dives: 50 - 99
    Location: The Deep South
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    I can be in perfect neutral buoyancy and then flip over so I am facing up with my tanks facing down and then I sink. WHY?
     
  2. BoundForElsewhere

    BoundForElsewhere ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: New York, New York
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  3. jgttrey

    jgttrey ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Houston
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    Unless you are venting air from your BC, the only reasons would be:

    1. Your breathing changes and you are unconsciously breathing more shallow when upside down, or;

    2. You weren't really neutral to begin with, but were masking that with some light finning. This is common, particularly if you normally have a heads up trim. You'd be amazed how many divers who think they are neutral will sink if you tell them to stop all motion (or will find they have to start breathing more deeply).
     
    Tournesol2000 likes this.
  4. victorzamora

    victorzamora Solo Diver

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    It's also possible your center of buoyancy didn't maintain the exact same depth during your roll over. A lot of people I've seen try to roll over end up a foot shallower or deeper than they started, and then their ability to fix buoyancy issues through breathing is flipped and/or unnatural so they end up losing control.
     
    Bowers and Jack Hammer like this.
  5. RainPilot

    RainPilot CCR Instructor Staff Member

    # of Dives: I just don't log dives
    Location: UAE
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    When you roll upside down, your lungs are now quite far below the second stage. That means the work of breathing increases, so you have to pull harder to inflate your lungs. This will feel like you are holding your lungs more full, and so you will tend to keep a smaller lung volume resulting in sinking.
     
  6. Doc

    Doc Was RoatanMan

    # of Dives: None - Not Certified
    Location: Chicago & O'Hare heading thru TSA 5x per year
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    That’s easy, you silly billy, gravity works in a downward direction. When you reverse down with up, that’s just gonna happen.

    There is a Distinctive Specialty that teaches this.

    There’s gotta be.
     
    StefinSB and victorzamora like this.
  7. CaveSloth

    CaveSloth Barracuda

    # of Dives: 50 - 99
    Location: The Deep South
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    This actually sounds feasible.
     
  8. Storker

    Storker Divemaster

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
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    There's also the pressure effect on the bladder to consider.

    1. You have no guarantee that when you roll over on your back, you'll stay exactly at the same depth. Sink just a little during the roll, and Boyle will take the wheel no matter whether you're perfectly neutral or just a tad negative
    2. Even if you manage to stay exactly at the same depth, your wing will be slightly deeper when you're on your back than if you're oriented with your back up. Again, the bladder will be just a tad compressed, and that's enough for Boyle to take the wheel again. Particularly if you try to just lie still on your back.

    (2) is of course not applicable if you're wearing a jacket BCD.
     
    Subcooled and Lorenzoid like this.
  9. divad

    divad Solo Diver

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    I always surface horizontal, then roll over on my back to lounge, stare at the sky, look at the birds, rest etc., and I always have to add air to the wing/drysuit.
     
    CaveSloth likes this.
  10. BoundForElsewhere

    BoundForElsewhere ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 50 - 99
    Location: New York, New York
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    Another mystery of the life aquatic solved by the Scubaboard gurus. Thanks, guys.
     
    CaveSloth, Doc and RainPilot like this.

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