Basic questions about construction methods

Discussion in 'Materials' started by foxfish, May 8, 2011.

  1. foxfish
    Joined: Jun 2008
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    foxfish Junior Member

    I am going to build a displacement 6m x 2.4m power cat.
    The plans offer aluminium or glass skin over ply.
    Q1 how difficult is it to weld aluminium?
    Q2 how much weight difference between the two methods?
    Q3 what about encapsulated ply construction?
     
  2. gonzo
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    gonzo Senior Member

    1-It is rather difficult
    2-It depends on the scantlings and building methods
    3-It is a good system
     
  3. foxfish
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    foxfish Junior Member

    OK thanks, so encapsulated ply construction is about laying ply over frames, glassing the outside, turning the boat over, knocking out the frames, glassing the inside & replacing the frames?
     
  4. PAR
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    PAR Yacht Designer/Builder

    Plywood building methods number a half a dozen or so, distinctly different types. Encapsulation is a choice for most, with some pretty much requiring it for success. Some modern plywood build methods don't require building over molds (what you're calling frames).

    Aluminum welding is like most anything else and requires some training and lots of practice. It's pretty much like sex. The first few times you had at it, you probably could barely please yourself, but with practice and some guidance, you managed to impress one or two prom dates. Same deal with welding, particularly aluminum.
     
  5. foxfish
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    foxfish Junior Member

    Well I am keen to learn about the best methods - I did train as a boat builder but that was 30 years ago & I must admit to not being up to speed on modern techniques, especially considering I have not worked in the profession for 25 years!
    Please tell me about the most upto date plywood construction methods?
     
  6. PAR
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    PAR Yacht Designer/Builder

    There are no "best" methods, just different ones. Each have advantages and drawbacks, just like anything else.

    A dissertation on building methods isn't best served here as it takes volumes (books) of text to cover all the bases.

    You're going to want to explore "taped seam" building , which has several other names; stitch and glue, tack and tape, goo and go . . . which generally describe aspects of the method, though each is a taped seam type build.

    On this site there are hundreds of previous threads about the processes, also check out Sam Devlin, Harold "Dynamite" Payson and Phil Bolger's work. Everyone now seems to have slightly different twists on the taped seam process.

    Then of course you can get into cored composites, which takes the process to the next level. Do some research and familiarize yourself with the methods. Have a look at the Glenn-L and Bateau.com sites and read their overview on the subject too. I would suspect there are UK based designers that have sites too.
     
  7. foxfish
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    foxfish Junior Member

    Thanks, I was particularly impressed with the Bateau site.

    I am most interested in encapsulating plywood however I would prefer to use polyester resin & glass fiber.

    I am planning on using 3 layers of glass on the outside & 1 layer on the inside before fitting out with structural bulkheads etc
    .
    It seem the main reason to use epoxy is because it is primarily a glues & will stick to the ply where as polyester may not hold on to ply & possibly delaminate from the wood! However, what if I drilled multiple 6mm holes through the ply before laminating.
    When the hull is turned, I could then sand down the excess resin that has filled the holes but the inside coat would adhere well the the exposed resin?
     
  8. Dean Smith

    Dean Smith Previous Member

    put it this way
    i employed 10 welders in yachtbuilding alu#It took em 5 years to get up to survey standard
    Plus you need a good mig setup, min 4500 usa , pulling gun and so on
    Stick to that sticky ****
    #
     
  9. TeddyDiver
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    TeddyDiver Gollywobbler

    Why on earth??? Destroying perfectly sound materials with some 2:nd class substitute and methods.. :rolleyes:
     
  10. PAR
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    PAR Yacht Designer/Builder

    Foxfish, Your understanding of building technique is shall we say that of a novice. This being the case, you should stick with the recommendations of the set of plans you decide to get.

    Your premise about polyester doesn't tell the whole picture, which is a complex subject. To simply it, just trust the industry professionals that have learned these lessons the hard way and use epoxy.

    In a nut shell polyester resin systems are weaker in every regard compared to epoxy. This means if the plans call for two layers of 12 ounce biax fabric over a structural fillet, and you employ polyester, this lamination schedule will not be up to the task and thing will break. Having your transom fall off when you slam the throttle wide open for the first time, because you elected to use an epoxy laminate schedule with a polyester layup, is a hell of a way to learn this lesson. Second, polyester isn't waterproof, epoxy is.

    Polyester fails because water get between it and the wood. The wood swells up from the moisture gain and pops the polyester off the surface.

    In short, use epoxy if you're going to build a taped seam boat. Jacques has done an excellent job of engineering these boats and polyester is quite a disservice, not to mention really not very wise.

    Once you gain some experience and understanding of the techniques, chemistry and engineering involved, then you could consider making some adjustments to a build method.
     

  11. Dean Smith

    Dean Smith Previous Member

    hey Paul , how ya doin, caught any cat fish of late and why cant you sleep
     
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