Seeking Advice on Warped Bottom Sub Planking

Discussion in 'Wooden Boat Building and Restoration' started by nbehlman, Feb 1, 2014.

  1. nbehlman
    Joined: Aug 2011
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    Location: CT

    nbehlman Junior Member

    This is my first boat building project. I'm building a Chris-Craft style warped bottom hull. I am in the process of dry-fitting the sub planking and I'm at what I think will be the most difficult part of the build. I'm trying to do the diagonal planking when the bottom meets the stem (see picture). The bends are getting pretty tight, and the 1/4" marine fir plywood doesn't like the compound curvature. Does anyone have any tips on how to execute this part of the build? Should I add any more framing to the stem area? I would appreciate any suggestions you might have.
     

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  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Change the angle, so the planks lay down sweet. By moving the plank around a bit, you'll find a spot it likes a whole bunch better. This is pretty normal to have to change angles, particularly towards the ends of the boat.
     
  3. SukiSolo
    Joined: Dec 2012
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    Location: Hampshire UK

    SukiSolo Senior Member

    Another way is to use 2 layers of 3mm ply, it is easier (usually) to bend. Put one layer on and then the other after the first one is glued. Best if supported inside a bit so that you can dry 'sandbag' or staple the second layer (as clamp) to avoid a void between the two layers. In extreme cases you will find making the ply in situ the only option!, ie a first layer of two veneers at 90 deg, then built up one veneer at a time. Slow but useful technique for certain shapes. Especially as it allows an ammount of true 3D shaping, with strategic knife cuts.
     
  4. rwatson
    Joined: Aug 2007
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    Location: Tasmania,Australia

    rwatson Senior Member

    2 layers is a great idea if you can. Putting them on the bow is structurally a great idea, as this is the 'striking surface' of any boat.

    Changing the angle is also really good practice, if you can. Sometimes the curve is just too severe in any direction.

    I presume you will be glassing and epoxying the hull - and not wanting a clear finish ?

    If this is the case, then you may find it useful to carefully cut shallow grooves across the face of the ply, making sure that you do the same cuts on both sides of the hull on identical bits. If you make them at even spaces in the direction of the bend lines, you will get a nice fair curvature. There is always fairing later to correct any aberrations.

    Also, there is nothing wrong with using strip plank techniques, of forcing panels together with temporary hold-downs etc and gluing them in place using spot welds with epoxy . You can then remove the temporary pressure tools later, for whole hull finishing. It looks like you have encountered a few of those sort of places in other parts of the hull already.


    If you are wanting a bright, exposed hull surface, consider thinner plywood, heavily re-inforced inside the hull, with epoxy and glass.

    Finally, if you end up having to put a lot of pressure on the plywood, to the extent that the back surface starts to fracture - put some 6 oz fg cloth and epoxy on the back of the plywood before you force it into shape, and let it cure. You can then exert some amazing bending forces with confidence that the stressed layers on the outside of the bend will not fracture.
     

  5. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    Try making the strips narrower.
     
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