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THE "PERFECT ( being horizontal ) TRIM" HOAX

Discussion in 'Basic Scuba Discussions' started by BLACKCRUSADER, Dec 27, 2020.

  1. Phishin

    Phishin Garibaldi

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    Why is it not just a question of trim control? If you can maintain your depth and control in an upside down, semi-reclined, jack-knife while pirouetting to “communicate” with those around you, you should easily be able to use those same skills to be in whatever the perfect trim for the situation is.

    Sorry, this is how I was trained to descend. First post!
     
    -JD- and Angelo Farina like this.
  2. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    To me, if you have to do a lot of work to stay in the orientation you want, you will not do that long. Unless you are really really motivated to be doing that.

    I'd love a clearer term than trim for the use as 'relation of centers of mass and volume'. As trim is more often used as orientation.

    Maybe just balance? Be in neutral balance? Instead of tail-heavy balance?

    If you have neutral balance (coincident centers of mass and volume), then orientation control is easy and you are likely to do it and not swim along kicking the bottom. Particularly as you will also be more streamlined that way and it will be easier to swim forward and to maintain depth when you stop.

    (Welcome.)
     
  3. dmaziuk

    dmaziuk Regular of the Pub

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    The thing about gravity is, when you're Michael Phelps, it doesn't rotate your hips. You do.
     
  4. Phishin

    Phishin Garibaldi

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    Attitude control!
     
    -JD- and MichaelMc like this.
  5. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    I think attitude still means orientation. The attitude of the aircraft, etc. Plus it also means your outlook toward the world.

    Mass distribution, but that is two words.

    Submarine analogies are hated, as subs are rigid and we are not, but subs use trim tanks to shift mass to get the mass volume relation they want to make the orientation they want easy.

    But scuba uses trim to mean both orientation and what we do to fix orientation (which is often changes to mass balance). So scuba's single term is confusing.
     
    Coztick likes this.
  6. Coztick

    Coztick Manta Ray

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    New word time!
    "GRAVITUDE"
     
    Phishin and MichaelMc like this.
  7. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    I like! People might not understand it on first use..., but I like it.

    Much as I like it, I think balance may be better.

    You are in neutral balance, as nothing is trying to tip you over in the water. Or something is, your balance is butt heavy. Or fin heavy, or head heavy balance. And balance is separate from orientation/attitude. As you can change your attitude/orientation despite difficult balance if you work hard enough.

    So the steps of proper weighing are:
    - weighting for neutral buoyancy
    - weighting for neutral balance (coincident centers of mass and volume/buoyancy)

    Note that Padi pool session 4 has the student "perform a weight check and adjust for proper weighting and trim." (2017 manual)
     
    -JD- and Lorenzoid like this.
  8. wetb4igetinthewater

    wetb4igetinthewater Instructor ScubaBoard Supporter

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    I don't. I see a number of students who have gone through fundies who get that impression. I'm not saying all students (trying to preempt GUE folks from piling on me for that).
     
  9. wetb4igetinthewater

    wetb4igetinthewater Instructor ScubaBoard Supporter

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    Are you talking about the center of gravity vs the center of buoyancy?
     
  10. MichaelMc

    MichaelMc Working toward Cenotes ScubaBoard Supporter

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    Yes. Neutral balance as having center of mass and volume/buoyancy in the same spot. Or nearly so.

    I'm happy for a clearer term. To me, any of these trim/orientation discussions are easier and clearer if we keep mass distribution and body orientation as separate issues.
     

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