Trim axis of planing boat.

Discussion in 'Boat Design' started by Henry Swanepoel, Apr 16, 2018 at 4:01 AM.

  1. Henry Swanepoel
    Joined: Nov 2017
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    Location: Gordons bay, South Africa

    Henry Swanepoel New Member

    About which axis or point does a boat trim when planing? Is it simply the CG or is it some other point?

    And am I correct in stating that when the vessel is static, the axis about which it will trim when mass moves on the vessel is the centroid of the water-plane area?
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    It gets more complicated when planing. The dynamic lift is dependent of shape and speed. It shifts with speed as the boat rises up on a plane because the shape and total surface area submerged change.
     
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  3. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    When planing, the static trim will be determined by the equilibrium of all the external non-inertial forces (hydrostatic, hydrodynamic, aerodynamic, mass) and moments around the CoG.
    I realize that the above is essentially a tautology, but is hard to say anything more than that without getting into the design details of the vessel.
     

  4. Heimfried
    Joined: Apr 2015
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    Location: Berlin, Germany

    Heimfried Senior Member

    That's right, but just a small trim changes the locus of the centroid of the water plane. So the next incremental trim motion has an slightly different axis and so on.
     
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