Draft when heeling a sailboat

Discussion in 'Stability' started by jessepietila, Oct 24, 2016.

  1. jessepietila
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    jessepietila Junior Member

    Draft change when a sailboat heels

    The draft evidently decreases when a sail boat heels (normal keelboat).

    So, how to calculate the change in draft due to certain section ?


    This question is to help me design a open transom with correct height for water to not flow into a heeling boat...... for a DIY sailboat.

    It´s about modern light displacement monohull,


    Thanks !


    Jesse
     

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  2. Heimfried
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    Heimfried Senior Member

    The floating position of a boat (given by heel angle, trim angle, draft) depends of the form of the hull (and ...). Is the draft helpful in case of a heeled boat when you want to know if water comes in?

    It is a question of the remaining freeboard in respect of a (changing) reference point (the actual lowest point in the open transom).

    I think, it will be neccessary to design a first hull and calculate its hydrostatic behavior completely, then do a second design and calculate.

    I did this calculation.:
    http://www.bootsphysik.de/rechner/bootx.php
    (if interested, use button "English" top right and use some buttons "i" )
     
  3. jessepietila
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    jessepietila Junior Member

    yes, surely the design process has begun in Rhino 3D with no hydrostatistical software / plugin.

    Than You for the link to Your calculative online software ! Should it be possible to change the main measurements for the design ?

    For curiosity this is something interesting I did find in internet,
    http://kspline.com/CudbyK2008aKspline.pdf


    Jesse
     
  4. Heimfried
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    Heimfried Senior Member

    If your software (Rhino) is able to create an fitting output in cartesian coordinates, I would load it up to my site and you could "play with your boat".

    Neccessary is a csv-Table (or Excel-File) like this:
    Coordinate-origin is at deepest point of keel at transom perpendicular. Row 1 shows the y-values of the vertical sections parallel to the center plane of the boat (125 sections) in mm, column 1 shows the vertical sections perpendicular to this (x-values in mm, 375 sections). The values in the other cells show the corresponding z-value, e.g. cell C3 value: "1220,6.." means at x = 14,6 mm; y = 7,5 mm; the corresponding point of the hull skin is 1220,6 mm above the base plane.

    (Comma is decimal sign.)
     

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  5. jessepietila
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    jessepietila Junior Member

    ok, let´s test it !


    Please inform me about some corrections I need to make to the hull..
    Obviously the design itself will still change and so on.

    I mean there´s no bulb modeled at the moment etc.


    The deepest point of the hull is at 0,0,0


    Jesse
     

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  6. Barry
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    Barry Senior Member

    A question to the sailboat designers

    If the sail is tilted at an angle and loaded, is there not a vertical down component due to the sail loading, which would increase draft.

    Ie more than just rotating the body, keeping the buoyancy constant through some tilt, then determining the draft.

    Which would make the calculation much more difficult
     
  7. Heimfried
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    Heimfried Senior Member

    Hi Jesse,

    sorry, the attached file (your post #5) is not of the proper data format. Please look at the picture attached in my post #4.
     
  8. Heimfried
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    Heimfried Senior Member

    Hi, Barry,
    I'm not a sailboat designer, just do some hydrostatical calculations.

    I think, there is not an additional increase of draft due to the force of wind attacking the sails.

    There is a lot of possibilities to resolute the wind force (Fw) into components. In my opinion it is sensible to take a tangential component (Ft), which is perpendicular to the arm between CoE and CoF, because these two (arm and force) create that torsional moment (heeling moment).
    The remaining component (Fu) - rectangular to the first component - points upwards.
    (Sketch attached)
     

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  9. jessepietila
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    jessepietila Junior Member

    Hi Heimfried,

    so the file ".csv" was correct... but how could I format the file to be suitable ?


    Jesse
     
  10. Heimfried
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    Heimfried Senior Member

    The suffix ".csv" (comma separated values) only means, that numerical values in this file are separated by a comma.

    e.g. 1.502,22.0,4,7 is taken as
    1.502 in cell A1
    22.000 in cell B1
    4.000 in cell C1 ...
     
  11. TANSL
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    TANSL Senior Member

    In all this discussion there is something that surely am not considering because I do not understand why calculate equilibrium waterplane in this case may be different from that of any other load conditions, a number of forces (weight, force wind passage to a band, etc.) acting on the boat.
    Since there is a Rhino 3D model, let's export it to any of the multiple programs that perform these calculations.
    Trying to be more precise, why not calculate the forces on the lower shrouds and stays, which is the force transmitted to the hull by the wind ?.
    What am I wrong?. I hope I have not said some nonsense. If so, you will notice me.
     
  12. jessepietila
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    jessepietila Junior Member

    Hi TANSL,

    yea great, my approach concentrates at the moment only to the hull, well to a bulb keel as well. Hence I am using OS X Rhino with no real (I quest) boat design analysis I am here to discuss.

    Having some experience on Grasshopper for Rhino I hope to find some use on it in near future.

    And yes I will drop my .3dm etc to have a look sooner when I have modeled the transom and a deck on it..

    Cheers,

    Jesse
     
  13. TANSL
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    TANSL Senior Member

    If you agree, I could use your model and make some attempt at Maxsurf, taking into account the wind force you want to use and the position of its center of application. I have to think about how to model the various forces on the boat and see what happens.
     
  14. Barry
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    Barry Senior Member

    The forces in the shrouds etc are not really of concern as they are internal forces. Once you compute the total force of the wind on the sail and where it acts, that is all that you need to determine the moment
     

  15. TANSL
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    TANSL Senior Member

    What I said in that post was nothing more than talk.
    Internal forces (do not understand well this concept) caused by the external force of the wind. (Is buoyancy an internal force?). But I think that neither you nor I have clear the model to study because I do sense that there is a component that can change the trim of the boat. But, as I said in my previous post, I would have to study in more detail how they act, where those forces are applied and how they change with the heel.
     
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