WL over or under chine?

Discussion in 'Boat Design' started by UpOnStands, Oct 16, 2017.

  1. UpOnStands
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    UpOnStands Senior Member

    Is it recommended to place the chine under or over the WL?
     

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  2. PAR
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    PAR Yacht Designer/Builder

    Wow, what a loaded question. There are a lot of reasons for developing chine runs the way they get done, all having affects on their placement. For example most like to see more vertical topside flanks, but this is just an aesthetic consideration, though the more vertical this panel, the better the speed potential in most sharpie shaped hull forms. With the chine exposed, you'll gain leverage as the hull heels, which may be something you want. You also gain considerable volume as it's immersed, which also may be desirable (or not). In the end, the chine is usually defined by the design goal targets, not an arbitrary rule of thumb or preference. Entry and exit points can be critical on some hull types, but mostly they fall where you need the volume, to meet design criteria.
     
  3. UpOnStands
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    UpOnStands Senior Member

    Thanks for the detail.
    The design brief emphasizes resistance to heel and hopefully some degree of planing so over the WL will be used.
     
  4. gonzo
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    gonzo Senior Member

    If large initial stability is a requirement, a submerged chine will be better. According to your drawing, that will increase beam.
     
  5. UpOnStands
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    UpOnStands Senior Member

    Understood, of course the beam would have to be altered to yield the same displacement. The figures are just for explanation.
     
  6. TANSL
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    TANSL Senior Member

    The initial stability is a parameter that corresponds to the boat at rest. Therefore, once the ship is in motion, you have to think about other things. If you want to increase the waterplane breadth for the planing, or near planing, condition, for example, a submerged chine will be very useful.
     
    Last edited: Oct 16, 2017
  7. goodwilltoall
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    goodwilltoall Senior Member

    I would think either completely submerged or above the WL chine along its whole length is more efficient than transitioning between the two, less disturbence.
     
  8. tom28571
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    tom28571 Senior Member

    Can you show a hard chine non full displacement boat where the chine is always under or always over the waterline?
     
  9. Mr Efficiency
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    Mr Efficiency Senior Member

    The diagrams in the opening post represent what ? A catamaran hull ? Not like any boat I have seen. So I don't even understand what sort of boat is being discussed. :(
     
  10. fredrosse
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    fredrosse USACE Steam

    It appears to me that the drawings first presented show only1/2 the hull, where the hull ends (submerged on the right side of each drawing) represents the hull centerline.
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm tipping it is some kind of asymmetric cat hull, but I really am guessing.
     
  12. UpOnStands
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    UpOnStands Senior Member

    At the moment the hulls are perfectly symmetrical and the panels are developable.
     

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  13. UpOnStands
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    UpOnStands Senior Member

    The first diagram shows a transverse cutaway view through outboard stbd hull - kept simple to focus on the point at hand.
     
  14. UpOnStands
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    UpOnStands Senior Member

    Actually the flat keel is full width, the hull centerline runs down the middle of the keel plate.
    There is 12-16 mm of foam on the outside with vacuum bagged uni/epoxy on top of the foam.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Are we looking at a sailing cat with a submerged transom ? That will make performance in light airs very poor. It is almost impossible to have a chined cat hull that is not submerged. the only way it would happen is with heavily veed bottoms.
     
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