straighten heel calculation ghs

Discussion in 'Software' started by emanuele82, Mar 12, 2009.

  1. emanuele82
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    emanuele82 Junior Member

    Hello every body,
    i would like to know how to find the torque moment to straighten a boat with heeling which is not 0.I know there's a command useful to discover what's the momentum to be applied.
    It should be useful to define ballast quantity and positioning
    thanks in advance.

    Emanuele
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Are you asking...how to calculate it manually or..how to find a "command" in the program to do this automatically for you?
     
  3. emanuele82
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    emanuele82 Junior Member

    yes,i would like to know how to calculate the torque needed to achieve a 0 heel once verifyed that it is > 0.
    As for instance...let's suppose we've a boat tha with a certain loading condition it is 2 deg portside..How can i calculate the torque moment useful to achieve a 0 heel?
    I already know the torque command, but, applying the maximum torque showed with the command it is not sufficient to straighten it fully.
    So,how do you proceed to find the correct amount of weight and transversal distance to achieve a 0 heel?
    NO METTER IF BY THE MEAN OF A COMMAND OR MANUALLY.
    Thanks a lot for your kind answer.
    Emanuele
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    Well, there are 2 basic ways to do this. Both are straight forward if you are a naval architect or a student of naval architecture. If you're not then of course this is somewhat more difficult.

    1) In your weight estimate and GA highlight all the individual items transversely. This will give a TCG either positive or negative, depending upon your sign notation. Once you have done this, you will see that the TCG is not zero, ie the centre of gravity is not on the centreline for the vessel.

    So it is a simple matter of reverse engineering the moment required to acquire a zero TCG. That is to say you arrive at a moment value (or torque as you are incorrectly calling it).

    2) With your hydrostatics you can obtain the value of GZ at the angle of list, since the centre of buoyancy is no longer on the centreline. This, when multiplied by the displacement, is another moment.
     
  5. emanuele82
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    emanuele82 Junior Member

    Ok i already knew this way...it is easy...i tough there was a command useful also to adjust trim which is a little bit more difficult although it is possible to achieve it by computing longitudina righting arm for that condition and multiplying it for ship weight.
    Thanks a lot.
     
  6. emanuele82
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    emanuele82 Junior Member

    ok i found the way...ghs command display also the moment/deg for trim...:)
     
  7. Martijn_vE
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    Martijn_vE Marine software developer

    At the angle of list GZ is always zero, otherwise there's no equilibrium. I believe you are referring to the GZ value at heel 0.0. This, multiplied with the displacement, is the moment you're looking for. Then the only variable needed to calculate the weight to correct this heeling moment is the distance of the correction weight to the centerline. Without this distance the number of possibilities is endless.
     
  8. Ad Hoc
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    Ad Hoc Naval Architect

    Martijn_vE

    Correct, perhaps i should have been a bit clearer, but you understood, as should any naval architect. Thanks for the clarification.

    BTW, Heel is a temporary condition, ie owing to wind or waves, list is permanent, ie TCG problem.
     

  9. Martijn_vE
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    Martijn_vE Marine software developer

    :D :D
     
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