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Symmetrical, yet tilted

Discussion in 'Sidemount Diving' started by stretchthepenn, Aug 29, 2017.

  1. stretchthepenn

    stretchthepenn Barracuda

    # of Dives: 200 - 499
    Location: Atlanta, GA
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    A little help from the hive mind, if you please...

    I'm having a problem with my roll attitude when sidemount diving. I've got both pitch and yaw under control (or so I'd like to believe), but for some reason, I'm always rolling to my right side and holding a 10-15 degree attitude.
    • My gear setup (Hollis SMS 100D, 2 x HP 120 tanks) is symmetrical.
    • None of my gear is riding up while underwater.
    • As far as I can tell, there's no torque being applied from twisted/pulling hoses.
    • I don't think I have any weird air bubbles in the bladder(s).
    • My spine is aligned correctly, so I'm not naturally leaning to either side.
    Once I've breathed the right tank down by ~400 psi and the tank pressures are equal, I start to level out a bit...but I'm not level even then, and it's time to switch back to my left tank.

    Any suggestions on what's causing the problem and how to remedy it?

    (EDIT: corrected para #3 for left/right)
     
    Last edited: Aug 30, 2017
  2. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    On a Nomad, it is (too) easy to get unequal air bubble on the L and R sides of the wing, esp if there is a bladder pinch in the neck area. Don't know about the Hollis.
     
  3. northernone

    northernone Great White Rest in Peace ScubaBoard Supporter

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    If it's consistent I'd just shift my weighting and carry on without finding the cause.

    Alternatively start dropping or swapping equipment until you find the part that's unbalanced.

    Perhaps a dive light on one side, muscle density, or wetsuit anomaly?

    Regards,
    Cameron
     
  4. bamafan

    bamafan Manta Ray

    # of Dives: 200 - 499
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    I had a buddy who bought a modded SMS 100 and one of the strap lenghts were off. I would recommend getting out a tape measure and checking the length of everything to make sure your harness is symmetrical. I would also swap tanks so that they are on opposite sides. See if this changes anything as you might not have a matched tank. If all that checks out I wouldn't be surprised if the dual bladder was trapping air. I have heard more than 1 person complain about them.
     
  5. victorzamora

    victorzamora Solo Diver

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    On the SMS100D, I think the bladder isn't 100% symmetric. The inflator on the right side can cause less air on that side than the left, causing you to roll right.

    Other than that, bamafan suggested swapping tanks which could be it. If they're PSTs, especially older batches, you can get some pretty aggressively non-symmetric tanks.
     
  6. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    Your description does not seem to make sense. You roll to divers right, yet making divers left tank lighter helps that...?
    How big an imbalance is the wing inflation hose itself? It is an asymmetric air pocket, but it seems maybe minor.
     
  7. guruboy

    guruboy Divemaster ScubaBoard Supporter

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    No guarantee the tanks are matched either.
     
    northernone likes this.
  8. stretchthepenn

    stretchthepenn Barracuda

    # of Dives: 200 - 499
    Location: Atlanta, GA
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    Derp. I was in a hurry when writing my original post, and I got it backward. When I breathe down the LEFT tank, my roll evens out. Good eye. I'mma edit my original post.
     
  9. stretchthepenn

    stretchthepenn Barracuda

    # of Dives: 200 - 499
    Location: Atlanta, GA
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    That's the puzzling part. I've been carrying the same minimal gear for shallow recreational diving, and I don't have anything TO drop.
     
  10. stretchthepenn

    stretchthepenn Barracuda

    # of Dives: 200 - 499
    Location: Atlanta, GA
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    I'll do that with the tape measure, and I'll look into the trapped-air possibility. Swapping the tanks probably won't make a difference, though... I should've noted that the problem started recently, and I'd been using the tanks for a few months without noticing roll problems.
     

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