Sailing canoe crossbeams

Discussion in 'Boat Design' started by Cedric Oberman, Nov 26, 2020 at 6:08 PM.

  1. Cedric Oberman
    Joined: Nov 2020
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    Cedric Oberman Junior Member

    Hi everyone,

    Looking at sailing canoe designs, many seem to have solid wood akas, some use plywood laminate crossbeams, and a few use aluminium tubes. On the face of it, the aluminium option is lightest and easiest, so I'm wondering why people tend not to favour those. Is it the lack of flexibility? Or that tubes would tend to rotate under torsion? Or sudden critical failure on exceeding the elastic limit? I'll be sailing in the sea, so the whole rig will need to take some strain and bounce back. Also, I'll probably have enough offcuts of marine ply to make laminate crossbeams but I'd like to keep the overall weight down where possible so, I'd be grateful for the benefit of the experience of others.

    All the best

    Simon.
     
  2. kerosene
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    kerosene Senior Member

    Disclaimer: No experience just speculation.
    my guesses.

    Wood:
    +can achieve good weight to strength with hollow spars (ply and wood strips to create a hollow box)
    +arguably easier to customize structure to have stronger points if needed for stays or other attachments
    +easy to make curved beams if needed
    -much more work than simply cutting aluminum profile

    Alloy:
    +simple continues structure
    +easy to make (buy)
    +good modularity with straight beams
    +easy to mount stays etc. (pop rivets) but doesn't allow for specifically designing for these loads
    -hard to create bent structures
    -I would think wood can be lighter depending on dimensions used
     
  3. garydierking
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    garydierking Senior Member

    There is nothing wrong with alloy crossbeams but I would recommend sleeving either internally or externally where the tubing crosses the gunwales to avoid buckling. If the tubing is thick walled then it's not necessary. Do not laminate a solid beam with plywood. Half of the grain is in the wrong orientation and produces a weak beam. Hollow wooden beams have been very successful. Check this simple tutorial: Hollow Crossbeams http://outriggersailingcanoes.blogspot.com/2020/09/hollow-crossbeams.html
     
  4. Tiny Turnip
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    Tiny Turnip Senior Member

    Simon, I'm guessing you'll be familiar Solway Dory? If not, do check them out. They've been doing laminated beams, very heavy, but now use alloy tubes, with a really neat locking mechanism, which cuts setup/rigging time to less than half what it takes me with lashings.
     
  5. Cedric Oberman
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    Cedric Oberman Junior Member


    Hi Gary,

    Thanks for your advice and the link. What timber would you suggest to use? The wood in my building supply depot seems to all be knotty softwood, I don't think it's good enough for this?

    Simon.
     
  6. DCockey
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    DCockey Senior Member

    What size sailing canoes? One person? Or larger catamaran/trimarans based, perhaps loosely, on Polynesian designs or similar?

    My guess is the reason is pragmatic. In many locations specific sizes of aluminum tubes in alloys suitable for marine structural use is not readily available in a range of sizes, and when available for "retail" purchase can be expensive. In constrast wood is more widely available for amateur builders, and can be cut to size and glued into assemblies using generally available tools.
     
  7. kerosene
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    kerosene Senior Member

  8. garydierking
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    garydierking Senior Member

    Softwood is okay but you want a fairly straight grain and only small tight knots. Hardwood is not usually necessary and is harder to bend if that's what you need.
     
  9. Cedric Oberman
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    Cedric Oberman Junior Member



    Hi Dave,

    Yes that's right; a single outrigger. Kind of like a Proa but not double ended. Only 14 ft long by 2ft (the main hull). The size is dictated by my living arrangements. I'd go bigger if I could. I like the idea of using wood for the crossbeams as it seems to suit the boat. People seem to use spruce as it's light and bendy but I would have thought softwood might be a bad idea. Maybe box it in with marine ply and epoxy?

    All the best

    Simon
     

  10. kerosene
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    kerosene Senior Member

    I think you are overthinking it. I have plans for the outrigger kit for rowcruiser, linked above.

    Spruce is often used for masts. Definitely good choice. Pine of any other cheap (yet decent) wood will be ok. and if access to quality wood is limited rather scarf shorter good pieces together than use long but knotty pieces.
    I can check the rowcruiser plan in a bit but I think it suggested glassing the solid cross beams. Land sailing folks glass their mast spars too.

    Your boat is so small that forces are limited - you don’t need to over think it. 2x2” (2x3” maybe better) solid pine would probably be almost a good solution.

    ladder (I am sure there is proper term for it) structure like in the storer outrigger plans (imaged here, only 30$) is better strength per pound.

    97CCD6AA-8F22-4B73-835D-8B3BEB5D3F79.jpeg
     
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