wind heeling moment equation

Discussion in 'Boat Design' started by Bassoom, Jun 25, 2005.

  1. Bassoom
    Joined: Nov 2004
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    Bassoom Junior Member

    hi everybody:

    i need to calculate the wind heeling moment for an offshore jacup for a range of heel angles.

    is there is anybody knows an equation to calculate the heeling moment which is afunction of heeling angle?
     
  2. dougfrolich
    Joined: Nov 2002
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    dougfrolich Senior Member

    Heeling Force=Righting Moment/Heeling arm
    Righting Moment=Weight of vessel x Righting Arm(GZ)
    Righting arm for SMALL ANGLES =GM sin(heel angle)
    BM=moment of inertia of WaterPlane/(diplacement lbs./64)
    GM=Center of gravity to Metecenter
    BM=Center of bouyancy to Metecenter
     
  3. Bassoom
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    Bassoom Junior Member

    hi there:
    thank u for your response, but i need an equation to help me in my calculations.
    i have the heeling arm equation:

    heeling arm = .17*10^-6 AV^2*cos^2(heel angle)/Displacment

    i need something like that for the heeling moment.
     
  4. Raggi_Thor
    Joined: Jan 2004
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    Raggi_Thor Nav.arch/Designer/Builder

    I think you have it all.

    The preassure from the wind is approx 1/2 x density of air x wind speed squared
    1/2 * RO * V^2

    The force is preassure x area

    The arm is the distance from the center of teh underwater profile to the center of the profile over water.

    Isn't that close enough?
     
  5. Bassoom
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    Bassoom Junior Member

    Yes i think that is enough
    thank u for your help
     
  6. Madrc570
    Joined: Aug 2013
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    Madrc570 Junior Member

    Hello, could you please tell me what 'RO' stands for
    Thanks
    -Madrc
     
  7. daiquiri
    Joined: May 2004
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    daiquiri Engineering and Design

    You have to start from the codes your design will have to conform to. In the Oil&petroleum industry, the most important codes are those of the API (American Petroleum Industry), NORSOK (Norwegian petroleum industry) and the ISO (codes 19900 through 19906). The ISO seem to have adopted the best of the two worlds (American and Norwegian) and is probably set to completely substitute the later two in the future. Of course, there are also rules issued by DNV, Lloyds, GL etc. The choice of the rules which the design will stick to will depend principally on what is written in the design contract.

    All these rules and standards give you the procedures, charts, tables and formulae for estimation of wind loads, which you will have to stick to. If you don't, the design and calculations will not be approved by the authority or by the client. So the first step is to carefully read the design contract and see what does it require from you.

    Cheers
     
  8. TANSL
    Joined: Sep 2011
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    TANSL Senior Member

    From what I understand Bassoom not want to know the force of the wind, but the heeling moment for various values ​​of the angle of heel.
    May it be correct to say that the heeling moment equals the displacement multiplied by the GZ value at each heel angle?
     
  9. Olav
    Joined: Dec 2003
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    Olav arch. nav.

    ro, also rho, is the greek letter ρ which usually stands for the density, like in this case.
     
  10. Olav
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    Olav arch. nav.

    Not necessarily so. This is only true if the vessel is at equilibrium at this angle of heel. The heeling moment may be larger, causing the vessel to roll to a greater angle (until equilibrium is reached), or lower, thus making the vessel roll to a smaller angle (again: until equilibrium is reached).
     
  11. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Hi TANSL,
    this is what I read in the opening post:
    As Olav said. You are correct that at the point of equilibrium the heeling moment has to equal the righting moment (as Dougfrolich has pointed out too), but what if the heel angle is required for a given wind force? In that case the wind-resistance calculations will have to be performed too.

    Cheers
     
  12. TANSL
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    TANSL Senior Member

    I agree, what I say is true only when the ship is in equilibrium. But at that moment, there is no doubt that the "wind heeling moment" is equal to what I say.
    It all depends on what it is exactly what Bossoom needs to calculate.
     
  13. NavalSArtichoke
    Joined: Oct 2013
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    NavalSArtichoke Senior Member

    I doubt Bossoom has been waiting for 8-1/2 years for the latest replies to his query. Check the date of his original post.
     

  14. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    LOL!!! :D :D :D

    You're right, Madrc570 is to blame!!! :p :p :p ;)
     
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