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Steel tanks butt up trim

Discussion in 'Sidemount Diving' started by Pedro1234, Jun 21, 2020.

  1. Pedro1234

    Pedro1234 Angel Fish

    I hope you can help me
    I can't adjust my rig to find a good cylinders trim. I have butt up trim.
    I will try to attach some pictures so you can see what I mean.

    I am using xdeep stealth classic with butt plate and loop bungees.
    Cylinders are 12l 232bar Vitkovice steels.

    The lower attachment point is 180 degree from the valve knob. Cord is about 5cm long.
    I can see that tank rotation is wrong but don't know how to fix it. Valves are not horizontal but pointing up.
    Loop bungees too short?

    Any advice guys..?

    Thanks for any help.

    Attached Files:

  2. grantctobin

    grantctobin ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 500 - 999
    Location: Chicago
    Are these images with the cylinders full? At 50bar?
  3. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    What would you estimate your tank buoyancy to be at the moment of these photos?
    -1kg? -4kg?

    Lol! @grantctobin beat me to it!
  4. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass Staff Member ScubaBoard Sponsor

    # of Dives: 500 - 999
    Location: Napa, California
    This was a good pic of yours to illustrate the issue:
    It appears to me that if your tank is not very negative at this moment, your right tank is indeed rotated counterclockwise. Tethered as it is by your lower attachment point opposite the tank valve knob, it is riding up on the leash, which counting the bolt snap appears to be a bit longer than 5cm. It can't be very heavy at this point to be doing that.

    I would examine how you are running your loop bungee to the valve horn opposite the tank valve. A simple loop carried forward of the valve and around the horn can rotate the tank this much if it is too short and/or too thick. Or you may be using a unique attachment routing that accentuates the counterclockwise rotation of your tank. You might consider a hip D-ring instead of your butt plate, with a bolt snap attached with almost zero leash length. You'll get less "climb" out of your tank butt that way, though depending upon your loop, it may ride low.

    Let us know how this works out!
    Thanks for posting!
  5. tbone1004

    tbone1004 Technical Instructor ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
    Tanks need to be 0 length. 5cm allows them to float up which is bad. Not necessary to have any length on the lower attachment point.
    Depending on how tight the loop bungee is, you can try rotating the lower attachment point up and out *more towards the top of the tank instead of the inside* as the rotation from the loop bungee can cause the tank to twist on itself and bring it up.
    Contrary to what you read, steel tanks are not impervious to becoming butt floaty and even with LP85's, I will lower them to a hip attachment point when they are about halfway empty.
    Make sure to measure the distance from the loop bungee to the lower attachment point on the rig, and make sure the distance between the lower attachment point and the valve knob is the same so the tank isn't trying to pivot on itself.
  6. mac64

    mac64 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 5,000 - ∞
    Location: Ireland
    D62E1324-9BF2-4223-B480-BB8A0E3F93FB.jpeg I don’t use a butt plate with the XDeep harness and my 12ltr steels trim perfect, photo is 12ltr lp steel at 50bar.
    P.S. sorry about the quality of the photo water was dirty
  7. Pedro1234

    Pedro1234 Angel Fish

    thanks for answers.
    At the photos tanks are around 80bar.
    My loop bungees are going simply around the valve knob. But maybe there are bit too short.

    Yeah now I think I know what to try next Will adjust my rig and try it in the water tomorrow
  8. Pedro1234

    Pedro1234 Angel Fish

    Hi again.
    So I've made bungee loops a few centimetres longer. Changed position of lower bolt snap. Now it's much better
    Next time I will try to attach tanks to drings instead of butt plate.
    Anyway its much better and I know where the problem was
    Thanks for help!
    RainPilot, mac64 and rsingler like this.
  9. racanichou

    racanichou Manta Ray

    # of Dives: I just don't log dives
    Location: Ottawa, Canada
    You can also try to attach to the drop D ring (the ones where your attach your but bag)

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