Building a stitch & glue boat in Fiji

Discussion in 'Boatbuilding' started by Saqa, Oct 20, 2013.

  1. michael pierzga
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    michael pierzga Senior Member

    You could but you will have difficulty bending it around corners. That cloth is very heavy and stiff. Normal tape seams on a small craft would use cloth half that weight.

    Ive never tried to cut heavy roving into tape...i think that the weave will fall apart as you cut.

    Give it a try. Adhere masking tape to a piece of roving then cut thru the tape and roving with razor sharp scissors.
     
  2. Saqa
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    Saqa Senior Member

    I am thinking along the lines of not cutting a "tape" as such, rather a really wide tape that would cover half a panel on either side of the seam
     
  3. michael pierzga
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    michael pierzga Senior Member

    I would endevour to cut that roving into tape that has its fibers running 45 degree. Fiber bundles dont like to bend 90 degree across a joint.

    The strength that you need is in the chine area. Think of a normal wooden boat with a timber chine log. You dont extend this timber chine log halfway up the topsides, only one or two inches at the chine.

    Taped joints normally specify 2 to 4 inches of fabric overlap on each side of the joint.

    This would mean 4 to 8 inch tape



    I would go 8 inch tape with that bulky roving to simplify cutting. Leave the masking tape that you cut thru on the fabric when you laminate to keep the fiber bundles from coming apart and making a mess.

    As for sheathing the boat, that dynel you have makes excellent sheating. Once you have taped the joints it could be used to cover the hull for protection and additional strength.
     
  4. PAR
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    PAR Yacht Designer/Builder

    No, roving isn't well suited (again). The builders in your area have to use finishing cloth in their builds. Some sweet talking, possibly bribery with some beer may be necessary, but I guarantee, they have some cloth.
     
  5. Saqa
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    Saqa Senior Member

    Is that because its a pita to use or actually weaker then tape?
     
  6. PAR
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    PAR Yacht Designer/Builder

    Roving comes in a tape or bulk roll form, just like biax and other fabrics. Roving is too heavy to conform well to seams. You need a lighter, less bulky fabric, such as cloth or biax.
     
  7. Saqa
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    Saqa Senior Member

    Will it be induce a structural issue if I manage to make it conform with weighting and pinning and such methods? If if doesnt I might be able to make it work if I try hard enough
     
  8. PAR
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    PAR Yacht Designer/Builder

    This is a poor way to learn about physical properties and material application suitability, not to mention learn how to engineer laminates.

    Try is. Get some roving and see if you can get it to go around a corner, while wetting it out with goo. Yes, you can force it, though this usually requires some sort of mold, it still has issues in this application. You can take our word for it or you can try it and learn what we already have.
     
  9. Saqa
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    Saqa Senior Member

    You are correct mate, I can see it from quite a number of posts back that it will be a pain to go around a sharp bend.... I understand that. What I dont have knowledge of is if it is bent and resined, will it become a weak point? Is the fibres in it different from the fibres in tape? Weaker? Not enough strands? Or what? I dont even know how to test it as I dont have tape to compare it with
     
  10. michael pierzga
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    michael pierzga Senior Member

    The loss of mechanical properties of the glass strand in a sharp bend are not important. Contact with the substrate is.

    A small boat ,using lightweigth cloth , will require a minimium bend radius of 25 mm
    This radius allows the builder to lay the impregnated cloth onto the joint , then compress it against the substrate.

    If the impregnated glass fiber does not contact the substrate in this radius ,you will have a weak joint

    Heavy glass fiber like roving may need a 40 or 50 mm radiused joint in order for the fabric to stay in contact with the substrate.

    Its difficult the make this large radius on a small boat

    If you lay the fiber 45 degrees to the joint as opposed to 90 you might be able make the roving contact the substrate at a smaller radius. At 90 degree you will fail
     
  11. rwatson
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    rwatson Senior Member

    That will be fine. Often lighter stuff is used successfully ( 200 gsm ) but this stuff will do a great job, even if it will use up a bit more resin than the lighter stuff.
     
  12. Saqa
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    Saqa Senior Member

    I am going to try to source some tape and cloth somehow first. If I cant then will fall back to the roving

    A similar boat to mine, the Mushulu 12 from Bowdige lists 4mm ply for the hull and 6mm ply for the stringers and frames in the BOM. Plus 200g cloth. Doesnt mention tape size or type on the webpage
    http://bowdidgemarinedesigns.com/Bowdidge_Marine_Designs_1/Magnum_12_construction.html

    I am using 9mm ply. It is tough stuff in that I was able toture the panels into the complex bow shape in the CAD drawings. Do I need a fg sheath for the hull for structural reasons? Can I get away with 75mm tape?
     
  13. Saqa
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    Saqa Senior Member

    I picked up a 60ml syringe from the vet and enlarged the nozzle to 3.5mm and used it to inject a bead of the thick epoxy glue into all the seams. Then used the point of a plastic knife to spread the resin onto the end grains in the vee formed at the seam. I let that sit till it started gelling. I mixed baby powder into more of the same epoxy till it was like cake icing and shoved it into the seams with a finger running along. Cleaned up as best as I could but concentrated on getting all the epoxy from the cup into the seam first before it started heating up. All the seams on the outside of the hull took 9 x 50ml batches of epoxy mix with 4 of those batches bing the filler for the fillets

    This was last night. After letting it set through the day I am now removing the wire stitches few at a time and using the jack plane to slice away all the mess from the ply and beveling the fillets down flat to the ply edges. Prolly will be at this most of the night, when done I will use a sanding board to radius the seams a bit
     
  14. michael pierzga
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    michael pierzga Senior Member

    Dont use fingers, use a spoon, coke bottle or home made radius tool

    When you use your finger you cant pick your nose , scratch your ear or drink a beer and the fillet radius is not uniform. A uniform radius...not to big, not too small is important
     

  15. michael pierzga
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    michael pierzga Senior Member

    Many times the spot weld technique is easier. A small blob of epoxy under each stitch . to glue the panels together

    Once cured remove all stitches, let these spot welds hold the panels in place , then prime and fillet the whole structure.

    The best practice with epoxy is to work green on green. Prime, fillet and tape in the same day
     
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