Trying to design a homemade catamaran..

Discussion in 'Multihulls' started by russmbiz, Jul 11, 2010.

  1. russmbiz
    Joined: Jul 2010
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    russmbiz New Member

    A friend and I are wanting to build a wooden catamaran. We're both very experienced in woodworking, but are so far unsure about how to waterproof the pontoons.

    So far, the dimensions that we've figured out are triangular pontoons, 12 inches wide, and 17 inches tall. That way we can get 3 sides from a single sheet of plywood. We will make them 12 feet long, possibly with a cone/pyramid on front, to cut through the water better.

    This gives us somewhere around 900 pounds of buoyancy. If any of this sounds wrong, please let me know.

    Now, what kind of plywood do we use? Should we stich and glue, or build a simple frame? We'd like the triangles to be sort of curved, but it isn't necessary. Do we cover with fiberglass, or just with epoxy?

    I hope you guys can help me get this all figured out. We're ready to start now.

    We're needing this to be as cheap as possible. Thanks in advace.
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    So how much work you are willing to do? You could make strip planked from any free timber left overs you find around and cover with glassfiber epoxy..
     
  3. Ike
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    Ike Senior Member

    There are many ways. One is to just paint it with a good marine paint. Another is coat it with epoxy resin. Next is use fiberglass and epoxy resin. If you do some searching on the threads on Design.net you will find lots of info on these.
     
  4. Richard Woods
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    Richard Woods Woods Designs

    Are you making a power cat or a sailing one??

    I'd expect you to use 3/16in plywood and 1in x 1in lumber where required

    No need to fully glass sheath it unless you plan to keep the boat in the water full time.

    Good luck

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  5. russmbiz
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    russmbiz New Member

    How would painting it keep the cracks waterproof? I imagine I have to epoxy the plywood together either way, right?

    Its a sailing cat. Would this just need to be exterior treated plywood from lowes, or does it have to be marine ply, coated with resin, with epoxy holding it together?
     
  6. bearflag
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    bearflag Inventor/Fabricator

    Two of the cheapest methods if you have low grade lumber are to make an Airolite boat using the Platt method or to use the Lindsay Lord method. Esp for the size boat you are looking for.

    Platt
    http://www.duckworksmagazine.com/04/s/columns/cupp/19/index.cfm

    Lord (out of print)
    http://www.amazon.com/Naval-architecture-planing-hulls-Lindsay/dp/B0007DRCCE

    If you can afford some more expensive wood, you might even want to make a cold molded hull since you have the wood skills.

    or Alternatively you could make it out of plywood. There are plans for the Tornado floating around the internet. I am sure you could modify those to accomplish what you want.

    The gist of the first two methods is as follows:
    Platt, minimalist materials in a skeleton wooden frame, with a thin membrane skin over it. You can put a thicker skin on it, or put Xynole or Kevlar etc over it if you want it to be bullet proof.

    Lord method is to do simple strip planking, using any quality of wood, Home Depot is totally fine. Just pick a relatively lightweight wood. Then fiberglass the inner and exterior layers of the wood and viola. Done. For your application, you could probably get away with even using Dacron or xynole or something cheaper than S2 glass.
     
  7. junkman
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    junkman Junior Member

    If at all possible you may want marine grade at water line and below Id think. :?:
    Maybe a decent question here, using exterior grade ply. Is there something on the market that penetrates ply before paint or resin etc. Maybe this would help keep wood grain from radiating outward in time and or perhaps resin inside of ply before constructing .

    I also wonder how well Lana board -1/4 in. from Lowe's / others, would hold up with glass and resin and this penetrating mix.
     
  8. bearflag
    Joined: May 2010
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    bearflag Inventor/Fabricator

    If you want to do it this weekend, and depending on if it is for practical use, and you aren't trying to win any boat shows, and weight isn't the most important thing in the world you can use the Epoxy garage floor paint as exterior sealant. You could even get it with sparkly bits in it! Not for structural use, but could make a impromptu covering.
     
  9. Alex.A
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    Alex.A Senior Member

  10. redreuben
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    redreuben redreuben

    Buy a second hand one !
     
  11. Richard Woods
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    Richard Woods Woods Designs

    Good exterior ply will be OK. Not sure whether Lowes sells "good" ply though. Home Dept doesn't

    Also not sure what you mean by "treated". Some wood treatments are acidic and glues don't work well

    I'm sure you've visited my website already. On the home page you'll see a link to some sample plans. The Pixie sheet may be of interest

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  12. bearflag
    Joined: May 2010
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    bearflag Inventor/Fabricator

    Always good to go to the local "pro" lumber shops. They are around everywhere, you just have to look for them.
     
  13. Alex.A
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    Alex.A Senior Member

    Hi - also building a cheap/small test bed cat.... looking for cheap alternative ropes/sheets/stays etc - non "marine" ie from the local hardware store?
    Also cheap sail material - see a lot of people using polytarp - is it ok and are there any other alternatives?
    For 14' cheapie.:confused:
     
  14. cavalier mk2
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    cavalier mk2 Senior Member

    Hardware store things are alright for a tester Alex. Go galvanized on blocks and wire and select your rope after comparing the properties-stretch,strength, uv etc...woven poly tarp works great using duct tape. I rig tested my sailing canoe with it and was able to get several years of sailing out of it after I worked out the best size. For full battens I used 1/8th" epoxy coated door skin (some were also glassed) on each side of the sail through bolted to each other with small fasteners. Get a big enough tarp so you only have to worry about taping the edges and color match your tape for nicer looking results. From across the lake they will never know !
     

  15. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    Cavalier's last sentence is the crucial one

    Sorry to be a party pooper, but please remember that human beings are land animals. We don't last long at sea without a boat under us

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
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