Building a Boat

Discussion in 'Boat Design' started by Cat Fish, Nov 24, 2008.

  1. Cat Fish
    Joined: Nov 2008
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    Cat Fish Junior Member

    Looking for your thoughts.
    I am going to build a flat bottom boat between 16 & 20 ft. I looked at a stitch and glue over plywood epoxy build. The epoxy, good plywood is very expensive to build. I was wanting to know if a one off boat ( all glass ) mold and polyester would be any better and cheaper to build. Thanks for any replies.:idea: :confused:
     
  2. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Hi CatFish,

    The process of building fibreglass boats from a mould is very much a mass-production technique. The mould itself costs substantially more than the hulls it produces.

    There are one-off techniques for mould building that can bring the cost down. But in general, they are only economically viable when dealing with complex hull shapes that have a lot of compound curves. A mould will almost always be at least as much time and effort to build as an actual hull, and so is only a good idea if it will really bring the cost per hull down significantly.

    For a flat-bottom boat in the size range you mention, it's hard to get any more economical than plywood. You don't need AA grade marine ply and West System miracle goop. My own boat, a Phil Bolger glass-over-ply design, is built with AC exterior ply and polyester, and is still in near-perfect condition after seven seasons. (I would strongly advise that you do NOT use polyester, though! It is a pain in the *** to get it to adhere to plywood, the catalyst ratios are finicky, it stinks like you wouldn't believe, and sometimes if the weather's not quite right you have to scrape all of it off and try again. Buy epoxy, even a cheap epoxy is easier to work with than poly.)

    Of course, if you don't mind the thought of cutting bevels in wood, you can always build a plywood boat the old-fashioned way, with no goop, and it'll probably be a fair bit cheaper.

    Ultimately, you have to go with what fits your budget. If you can't afford top-end everything that'll last 30 years, then build what you can with the stuff you can get. Sure, it might last only 10 years, but that's 10 years in which you have a real boat to enjoy instead of just a drawing of something fancy and an incomplete budget spreadsheet.
     
  3. Cat Fish
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    Cat Fish Junior Member

    Ha, Matt

    Thanks for the reply. What I was thinking was to cut out the panels from cheep ply and cover with thin formica then put boat together in upright position. Mold the corners with clay and spray with PVA, gel coat then layup.:D
     
  4. marshmat
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    marshmat Senior Member

    Sounds like more effort than it would take to just build in ply.
    AC exterior ply holds up OK in the marine environment; if covered with fibreglass it lasts quite a long time. You could build a mould and go the glass route if you want, but I'm fairly sure you'd get a cheaper boat that's just as good if you build in plywood to start with.
     
  5. Cat Fish
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    Cat Fish Junior Member

    Matt you are probably right, go with a/c ply and epoxy. thanks.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Cat Fish, I'll second what Matt has to say, except that I would never use polyester on wood. It can be done, but the end result, if done well enough to insure waterproof, is much heavier then need be. Vinylester is a much better choice, because you can use less of it. Epoxy (as you've surmised already is the preferred goo on wood)

    Which flat bottom 16' to 20' design(s) are you considering? If designing yourself, do plan to explore the scantlings enough to cover the weaker home construction grade materials. This can be done several ways and is generally a moderately simple engineering exercise.

    A one off, all 'glass boat could be built, without a traditional female mold. You could use one of several different method.

    What are your desires, in regard to boat performance, tasks it will need to carry out, average number crew including their gear, budget, general operating area, etc. Also it would be helpful to know your particular skills, tool availability, building experience, as these all affect design selection and project success.
     
  7. marshmat
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    marshmat Senior Member

    Had I known at the time, PAR, I would have gone with epoxy. And I definitely do not recommend polyester on ply. It can work but it is such a pain in the *** to get it to work.
     
  8. Cat Fish
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    Cat Fish Junior Member

    Thanks Par.

    Boat, flat bottom shallow draft jon boat style but extra wide.
    two three people, two bait wells and all the normal stuff
    skills, I built 4 different one off center consoles molds and the consoles
    replaced 3 or 4 half and full boat decks a couple transoms, some different small molds & parts, a few rebuild boats from top to bottom and so on you get the idea ( back yard boat fixer upper )
    Tools, more than I need, that's If I can find them in the shop, you know what I mean!!!
    Budget, low but do it right
    Operating area, about a nine car enclosed garage.
    Skill, I can do it with one off mold or whatever!
    I just want to ck out all my options as I don't want to build a piece of crap boat, I will spend what I have to in order to do it as best I can.
    Do you think a all poly or vinyl ester glass ( through away mold ) boat would be any better or cheaper to build than a epoxy over ply? I know either way would be a great boat if done right.

    Thanks very much for taking your time to reply.
    I appreciate your or any one's suggestions
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    In the size you're building, an all ply, taped seam with a light weight exterior sheathing will be the cheapest. This is because the basic hull shell forms the mold for the sheathing and it requires little internal framing structure to be built.

    As far as this type of build being easy, well that's a subjective issue. I don't recommend taped seam boats for novice builders, unless it's quite small. The reason is the "goo factor" which is my term for working with fabrics, fillers and resins. Even with epoxy, which is easy to play with then the "esters", it's still messy, can easily be screwed up and not especially nice or your hands, cloths and work spaces. It takes a little exsperence to get a feel for goo work, which is best done on a small project.

    With 'glass construction types, you have a lot of fairing to do (read, sanding your butt off), but not so much wood working. The goo factor is very high and you ability to generate a smooth, lump and hollow free surface is tested everywhere.

    A plywood panel is essentially pre-faired across most of it's area. The seams need to be addressed, but that's about it. This is one of the many reasons it's so popular as a building material.

    It's often cheaper to fix up a sound 'glass hull then build a new one. Replacing systems and drive train isn't as difficult as building a boat then still having to install systems and a drive train.

    In the current market, there are thousands of boats, just sitting under tarps, carports or lying in a backyard dieing a slow UV riddled death. These can be had for a song, sometimes free, if you just get it our of "her" garage.

    Strip the hull, repair the issues, paint it and install the engine, controls, whatever that you would on a new boat. With your experience at repairing transoms, soles, etc., you shouldn't have too many issues with a tired old hull.

    A Jon boat is a simple build. There are a few in 'glass, but as a rule the relatively flat panels that make up these boats, don't lend themselves as well as plywood in construction.
     

  10. Cat Fish
    Joined: Nov 2008
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    Cat Fish Junior Member

    Par, Thank you for your time. Well it sounds like the best way for me to go is with epoxy over okoume ply. I will end up with a lighter boat and lower draft number, but still have a solid boat.

    Now to start the building material gathering process.$$$$$
    Thanks again Par. :cool:
     
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