Strength of a small sailing canoe?

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

  1. nukisen
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    nukisen Senior Member

    I am attempt to build this one for summer use if I am still in sweden this time.

    Want to use a wooden board plate 3,1mm and cover it with epoxy in the inside and outside. The boat will be about 4 meters. Is it necessary to add some longitudinals or it will keep the strength to carry my weight (0,1 ton):rolleyes:

    How do I calculate?
    Or anybody is able to tell right the way?

    As I have no idéa about strength calculation.
     

    Attached Files:

  2. ancient kayaker
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    ancient kayaker aka Terry Haines

    Jan: I could not open the CAD file. It would be easier to understand with a few ortho views, or at least beam, draft, displacement, daggerboard and sail area data. Is "wooden board plate" the same as plywood and is that being used for the hull or the daggerboard? Good luck with the job hunting.
     
  3. nukisen
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    nukisen Senior Member

    Thank you Ancient!
    Actually I do at least gets some anwers and questions about me and my proffesion after I have recieved a lot of help from people in this forum.

    measurement in millimetres
    (LOA) 4000
    (Beam) 752
    (Displacement) 130 kilo
    (hull weight) 25 kilo

    My attempt was to use the board and epoxy for the whole construktion.
    Both shell and daggerboard as well as the three framing bulks.

    I have attached the freeship model instead. Note that the bulkheads not in this one.

    Also I do hope to see some more sailing photos from your boat this summer Ancient. ;)
     

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  4. nukisen
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    nukisen Senior Member

    Oh sorry I did forget about the material.
    I have attached a pic as I don´t really know about the english name of this.
     

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  5. Itchy&Scratchy
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    Itchy&Scratchy Senior Member

    Thats masonite, or hardboard,

    basically just compressed cardboard.

    Not ideal boatbuilding material, but could be ok , depends how you plan to seal it.
    Itchy
     
    Last edited: Jan 28, 2010
  6. nukisen
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    nukisen Senior Member

    Thanks Itchy!
    I will seal it with glass and epoxy. About 1mm outside and inside maybe little thinner.
    As this material would be totaly swampy if gets contact with water.
    I also wanted to try build it out of aluminium but I am not able to weld alu as I have no machine for this.
     
  7. souljour2000
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    souljour2000 Senior Member

    That stuff is fairly heavy Nuk...I guess if you have a large supply of it...but it is less than $ 20 for a 4x8 sheet here in the US so it is cheap....but that would be the last stuff I would ever use...too heavy as I said...just me...one thing good about it..it is very flexible and strips of it would be easy to work with..it is floppy but just stiff enough too hold curves well...
     
  8. nukisen
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    nukisen Senior Member

    Yes you are right souljour.
    It is cheap. It is very flexible. this makes the developing damn easy, also juste because it is so cheap and easy to handle my thought was to leave the the plug inside the epoxy material. Next time I can easily do a new one.

    about the weght I have calculated hull wight about 25 kilo. I am able to build the hull about this waight in this material already calculated about it.

    Thanks for the oppinion soul!
     
  9. ancient kayaker
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    ancient kayaker aka Terry Haines

    I have reservations about the masonite material. According to Wiki "In 1996, the Masonite corp. lost a class action suit brought by homeowners whose Masonite siding had deteriorated beyond the point of repair. The jury found that Masonite siding had rotted and swelled and a fund was established for homeowners to seek some reimbursement for the costs associated with replacing the Masonite."

    I have never used masonite for anything remotely resembling a boat so the following is just my humble opinion. If others in the forum have used it their opinions should receive more weight.

    You will not be able to scarf it although it should take a butt joint OK, but it will need wider than usual butt plates because the back (inside surface) of the material peels easily. Once the hull is completed it will be stronger once it is glassed, but it is going to be a heavy boat. For plank material glassed both sides the strength resides in the glass layers rather than in the material sandwiched between. The thicker this material the stiffer and stronger the hull within reasonable limits. Thus a light, thin material such as cedar (balsa is sometimes used) is better choice than a heavy, thin one such as masonite. For such a thin inner layer, thicker glass layers may be needed.

    A 13 m masonite plank will be very fragile and difficult to handle because it is both heavy and weak. It may be also a problem using the stitch and glue method to join the seams if the wire stitches pull out of the material so test this first. Since the inner surface of masonite is weaker than the outer surface you may need extra wide tape and more epoxy fairing inside the seams.

    You can use my usual construction method which works well with thin, floppy planks. I glue thin wood strips along the inside edges of the sheer planks (layers 4 & 5 in the Free!Ship model) while flat to reinforce it, about 10 mm x 15 mm should be OK. At the chine edge the wood can overlap the masonite edge by about 3 mm. When the sheer planks are bent around the frames you can bevel these edges for the bottom planks. Frames can be permanent or temporary. The wood strips along the upper edge of the sheer planks will become the inwale and serve to glue on the deck.

    Test the glue you intend to use on a sample of the material to ensure it bonds well and is not absorbed into the masonite before it can set.

    25 kg sounds about right for the masonite on its own. Add wood, epoxy, glass and paint etc. and it will be closer to 40 kg IMHO.
     
  10. hoytedow
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    hoytedow Carbon Based Life Form

    My parents' home had Masonite siding on one area that lasted 50 years before it went bad. I still would not use it for hull building, preferring thin lauan mahogany for superior stiffness and lighter weight. Compare prices. Good luck.
     
  11. nukisen
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    nukisen Senior Member

    As calculated by the weight specification from seller the plates density is about 1,0. Also about the same as epoxy.

    So I am convinced about the weight will stay close to 25kg. If the strength is enough with this material.
     
  12. gonzo
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    gonzo Senior Member

    I would not use masonite. You will be better off with underlayment plywood.
     
  13. ancient kayaker
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    ancient kayaker aka Terry Haines

    Not sure what you mean by a plate density of 1.0, presumably that's the specific gravity. So a sheet of masonite will weigh 8 x 4 x 1/12 x 1/8 x 62.4 x 1/2.2 = 9.5 kg. A sheet of 3 mm marine ply weighs less than half that, is at least as strong and is known to work well with epoxy and glass.

    For my own smaller, undecked paddling canoes, which are intended for flatwater use I use 3 mm marine ply without glass; they use from 1 to 1-1/2 ply sheets and weigh in from 8 to 10 kg which is great for portaging. For a larger canoe intended for sailing it is common to use 4 mm ply or cedar strip and glass it on both sides. If using non-marine ply most folk use 6 mm. Masonite is also available in 6 mm (actually 1/4" or 4.23 mm) but that would be prohibitively heavy.

    You will need about 3-1/4 sheets according to FreeShip, say 33 kg for the masonite. Other than ply, I used only 3.5 kg of wood in my 3 m canoe which has no deck or keel. Adding the deck and keel, plus cockpit coaming and daggerboard trunk, and allowing for slightly thicker pieces for a longer boat intended for sailing, will triple that. Now add the glass at about 2 kg per side, plus finish, seat, footrests ... but it's your choice.
     
  14. nukisen
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    nukisen Senior Member

    Thank you guys!
    So if I uses the ply then I will be able to build this boat as in the first pic I uploaded. And it will be holding together. Now my next step is to go find this ply material as the most dealers here sell 11mm ply.

    Thanks for the advice!
    I have to rethink the material.
    Also I have thinking about make ribs out of plank to use. As this boat will be very easy to build out of plate material I agree about the ply material is the best.
     

  15. hoytedow
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    hoytedow Carbon Based Life Form

    Try to find 4mm to 6mm thickness ply. 11mm is too thick, except maybe for seat.
     
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