Building a 12' cold-moulded dinghy

Discussion in 'Wooden Boat Building and Restoration' started by Graham Tapper, Mar 29, 2019.

  1. Graham Tapper
    Joined: Mar 2019
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    Location: Devon UK

    Graham Tapper Junior Member

    Hi ,
    I am making myself a light ply pulling and put-put dinghy to be propelled with a classic Seagull 40+ outboard.
    I began about late Jan 2019 and am now making a few final fairings to the plug or mould. I intend using three layers of 3mm marine ply.
    It follows quite closely the lines of the Firefly sailing dinghy designed by Uffa Fox. I have widened and deepend the transom and reduced the keel rocker. More info and photos can be found here on my Blog:
    Head for the Hills: How to build a Dinghy in Cold Moulded Ply. http://moggo-blog.blogspot.com/2019/03/cold-moulded-dinghy-build.html
    Hopefully I shall be nearing completion early July ready for use on the several Estuaries around south Devon.
     
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  2. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    It looks like a great project. Best of luck to you. That is a pretty large layup to do alone. I am a little curious as to the sides and bottom being the same thickness. But perhaps the 3mm at 3 is just about 3mm overkill on the sides and easier to build uniform.

    How will the ply be held?
     
  3. Graham Tapper
    Joined: Mar 2019
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    Location: Devon UK

    Graham Tapper Junior Member

    The ply will be laid in 2" wide strips laid diagonally with the middle layer laid longitudinaly. Held in place with temporary staples using a staple gun. I am being guided by a good book "Clinker Boatbuilding" by John Leather. The last few pages has reference to the method of building in cold moulded ply. Its not vacuum bagged, so speed is not necessary and the cascamite resin glue gives ample time to manouver (24 hours to cure). Thanks for the good wishes. Watch this space !!
     
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  4. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member

    Nice looking boat. Back in the 80's I took a boatbuilding class in cold molding and we built something similar but a bit smaller. We used staples as well to hold the strips in place while the resin set up. Works great. We removed them after. The finished boat was very light but strong.
     
  5. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    Did you guys use metal or plastic staples?
     
  6. Ike
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    Location: Washington

    Ike Senior Member

    Metal. I think they were copper? Long time ago. I would probably use monel. I have used them on other boats mainly in upholstery. Supposedly they will never corrode.
     
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  7. Doug Lord
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    Doug Lord Flight Ready

    Thanks. I wonder if plastic staples could be removed?
     
  8. JamesG123
    Joined: Mar 2015
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    Location: Columbus, GA

    JamesG123 Senior Member

    Why would you?
     
  9. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Looks ugly under clearcoat
     
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  10. Graham Tapper
    Joined: Mar 2019
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    Location: Devon UK

    Graham Tapper Junior Member

    I intend using metal staples through thin cardboard "washers" to make removal easier and to avoid disfiguring the ply. There are some staple removal tools on the market but a 1/4" inch chisel will do just as well. Using washers will also make removal easier. Hopefully my 3mm ply will be delivered today and I can begin the build proper. The mould has become very labour intensive and still requires a little more fairing.
     
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  11. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    My favorite staple puller is a mini wire cutter. You lever it on a thin shim.

    I have a plastic stapler for foam work. It mightbe trouble here.
     
  12. JamesG123
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    Location: Columbus, GA

    JamesG123 Senior Member

    Ah.
     
  13. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Graham Topper

    The first set of staples, holding the base layer to the mold, can't be removed. Otherwise, the base layer will simply fall off the mould before subsequent layers could be added.

    The heads of the staples holding the intermediate layers will never be seen. So why bother removing them.

    I hope your mould is easily disassemble. It will need to be pried out of the finished hull. Countless staple prongs will be exposed. Cut or grind them off. Trying to pull them out will inflict great damage to the plywood. If you're going to clear coat, use monel or titanium. These metals won't discolor the wood. If you're planning on opaque paint then any staple would do.
     
  14. fallguy
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    fallguy Senior Member

    When you use staples to strip plank a canoe; you remove them before glassing.

    When you cold mould, if you don't do the entire layup in the same day; would it be theoretically possible to remove the staples from the outside, then continue if the part stays true to the frames?
     

  15. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Yes, but it usually takes a few layers before the hull will retain its shape. Since only the outer most layers will be seen there is little benefit in removing them.

     
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