Strength of a small sailing canoe?

Discussion in 'Boat Design' started by nukisen, Jan 27, 2010.

  1. nukisen
    Joined: Aug 2009
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    nukisen Senior Member

    looks like it wouldn´t be impossble to get 4 mm.
     
  2. magwas
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    magwas Senior Member

    I have made a boat model out of that. It initiated the post http://www.boatdesign.net/forums/materials/epoxy-not-waterproof-30616.html Okay, the main problem was with the resin I have used, but:
    When it gets water, the whole thing is damned. It blubbers in a way which deforms that (admittedly too low quality) resin.
    I have found it appropriate for model building however, steps of stitch&glue construction are the same with it as with plywood, but it thinner and cheaper.

    However if you think about it as a core material for glassing... Then simple paper cardboard might be just enough for such a hull. It is just a guess, I don't know much about glassing.

    Be careful, because freeship marks your model as not developable (press ctrl-d in perspective view). There is a level of area error in layer 0 which might be significant. Check your plan with a model before building.
     
  3. nukisen
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    nukisen Senior Member

    Thank you magwas!

    I have already made a papermodel of the developed plates in scale 1:9.

    Worked perfect!

    I am thinking about build it with using the cardboard as a plug. And only use glass and epoxy. Then I don´t have any organic material in it at all. As I have found the epoxy almost for free. This is a good option I think.
     
  4. ancient kayaker
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    ancient kayaker aka Terry Haines

    The red areas that pop up in FreeShip are not necessarily undevelopable. The numeric errors it provides in the Plate Development window are more useful is this respect; up to a few tenths of a percent virtually any material will bend to shape but beyond that success may require more effort. Of course, each layer has to be identified to FreeShip as developable before it will even try!
     
  5. magwas
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    magwas Senior Member

    This is why I used the word "might". Is there any good rule of thumb to determine from to determine from the numbers whether it would be still developable?
     
  6. ancient kayaker
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    ancient kayaker aka Terry Haines

    If you have data for the material take the yield point stress and divide by the modulus of elasticity, which will give you the distortion per unit length at yield, or yield strain, assuming both data are in the same units of course! Yield strain is dimensionless so metric or imperial units will give the same result. A value greater than the edge error should be OK.

    Typical woods for which I have mechanical data have yield points of the order of 0.5% of their modulus of elasticity, indicating they can tolerate edge errors up to about 0.005 as displayed by FreeShip in the Plank Developments window. I have verified this up on a hull plank with 0.004 edge error. That was not too tricky but it definitely felt near to its limit.

    FreeShip values apply only to thin planks, using planks of significant thickness would cause earlier failure I imagine.

    Of course different woods and different lots of the same wood will vary, but that is the guideline I use for okoume marine ply. Wood will bend a little further given time, and solid wood can, of course be steamed to sharper bends than this.
     
  7. magwas
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    magwas Senior Member

    Thank you for the explanation.
     

  8. nukisen
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    nukisen Senior Member

    Woaha!
    Thanks for your post Ancient. This I have to calculate about.
    Seems like I am able to learn something!

    Great!
     
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