Not exactly a design question...

Discussion in 'Boat Design' started by Jim Gallacher, Jun 6, 2012.

  1. Jim Gallacher
    Joined: Jun 2012
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    Jim Gallacher New Member

    Hello, I am interested in learning how to develop the chine panel patterns for any chine craft utilising the data on the traditional triple view of boat plan, profile and frames elevations but without using computers, rather using the curves from lofted drawings at for example 1/8th scale. I know I could work backwards by trial and error offering up an oversize plank to a backbone and frames but I would rather learn to do this accurately through drawing. Does anyone know if this is possible and if so how to undertake this? Attached is an elevation for the double chine rowboat Firefly, and establishing the true flat panel shape for the top chine which curves in 3 dimensions is baffling me. I have scoured the internet looking for this knowledge and purchased Wooden Boat's Getting Started Lofting and asked Gavin Atkin. Any help greatly appreciated. Thanks, Jim.
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    It isn't developable from sheet by the looks of it, not the bottom anyhow.
     
  3. tunnels

    tunnels Previous Member

    i am lazy so would say draw it out full sized on the garage floor or garage wall and take it from there !!. or just simply make the boat and be done with it !!. things have a habit of falling into place once you clear the wood so you can see the trees or the other way round ! what ever . all full sized drawings revell a lot and everything become clear . :p:D
     
  4. SamSam
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    SamSam Senior Member

    I'd be interested in knowing how to do that also. I would think though that you would need some numbers and angles relative to the baseline and/or the centerline. Like for the bottom panel, distance from baseline to station junction at centerline, length of station line from centerline to chine, and angle of bottom station line relative to centerline or baseline. All of which could be measured from a large sized drawing I suppose, and pretty much just the end view needed if you knew the station spacing distances. That would give you a set of numbers to loft from, the more stations, the more accurate you get, but I imagine there would be some trimming and fitting no matter what unless you have an unlimited number of stations like a computer can generate.

    I really like the shape of it. Is the 'Firefly" an old established design or something? Who designed it?

    I believe what you mean is a single chine boat.

    [​IMG]
     
  5. johneck
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    johneck Senior Member

    The body plan provides the key data you need. The lengths of the edges at each station need to be measured and transferred to the wood. The keel panel needs to be bowed slightly to make the ends rise. The side panel needs to be "bent" using the values of the bow of the bottom panel plus the length of the bottom panel. The bow needs to be rounded in order to make that shape (which may not be developable). I would suggest making a scale model in cardboard or construction paper to make sure it works properly before going to wood and full scale.
     
  6. waikikin
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    waikikin Senior Member

    Use girths & triangulation.
     
  7. SamSam
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    SamSam Senior Member

    That sounds interesting.
     
  8. daiquiri
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    daiquiri Engineering and Design

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  9. Earl Boebert
    Joined: Dec 2005
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    Earl Boebert Senior Member

    Here's the classic paper on development by S.S. Rabl.

    Cheers,

    Earl
     

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  10. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    This from Sam Rabl will give you something to puzzle over......:p

    Rabltext1.jpg

    Rabltext2.jpg

    Rablplate28.jpg

    Rablplate30.jpg
     
  11. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Look you can play with triangulation and other techniques, or you could just build a scale model and pull the panels off that. It's simple, rewarding and you'll be close enough to cut full size panels (over size, then trim to fit). The bottom bow sections will test your ability to convince plywood to fit, but it should be close enough to plank. You can always put a horizontal cut in the last few feet of the forward bottom panel and fill with fabric and goo, to make it fit.
     
  12. SamSam
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    SamSam Senior Member

    The object isn't to build a boat but to learn how to develop panel patterns from any set of plans.
     
  13. philSweet
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    philSweet Senior Member

    Then you want to pursue the Rabl paper in earnest. The girths and triangulation works IF you know the panel is developable to start with. But the method can also be blindly applied to nondevelopable surfaces with frustrating results. So you have to go through the process of developing the surfaces first. Then you also have the frame shapes to fit to your plating.

    But like the others have said- a sheet of hobby foamboard and an Exacto knife and poster board and you can loft that boat so as to cut full size panels 1/4 inch oversize with some confidence.
     
  14. DCockey
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    DCockey Senior Member

    Any particular reason for your statement? Looks developable to me though the frames and transom edges would not be exactly straight lines if the surface was developed perfectly.
     

  15. DCockey
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    DCockey Senior Member

    The triangulation method properly applied is usually better then "close enough" for most developable surfaces with curvature which varies sufficiently gradually provided sufficienly narrow triangles are used.

    But except for special cases the triangualtion method isn't exact if the surface is assumed to have continuous slope curvature. Rather it corresponds to the development of a similar surface with slope or curvature discontinuities across the radian lines. The magnitude of the error becomes smaller as the triangles become narrower.

    There are "exact" methods for graphical development of arbitrary developable surfaces but they are quite complex.
     
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