Boatbuilding roadbumps

Discussion in 'Boat Design' started by SPI-sail, Jun 19, 2008.

  1. SPI-sail
    Joined: Jun 2008
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    Location: South Padre Island

    SPI-sail Total noob with a dream

    Im building a slightly tweaked version of Bolger's Windsprint and have so far all the necessary plywood parts cut out. Some questions...

    I have a bunch of fiberglass cloth in 3x3 foot sheets, can I just cut these into strips to substitute fiberglass tape and cover them in fiberglass resin?

    For butting the plywood, will fiberglass cloth and resin work?

    I plan on covering the bottom of the hull with fiberglass cloth and fiberglass resin, and then sanding, what kind of paint should I use?

    For the inside of the boat, can I just apply a coat of fiberglass resin on top of sanded plywood without the cloth underneath?

    Should I use fiberglass resin or marine wood glue when attaching the gunwales to the side with clamps?

    What is the difference between fiberglass resin and epoxy?

    Sorry so many questions but I have a lot of building time tomorrow and would hate to waste it.

    Edit: I just had a idea I thought I would through out there... In theory, could I build a plastic glass type window on the hull so I could see underwater?
     
    Last edited: Jun 19, 2008
  2. Knut Sand
    Joined: Apr 2003
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    Location: Kristiansand, Norway

    Knut Sand Senior Member

    I can give you some of my meanings, others will pop up....

    First; you can use (at least, to my knowlegde) Vinylester resin + glass, polyester resin + glass, epoxy resin + glass. For stronger things replace glass with carbon, boron, kevlar, whatever, but not all types of mat mixes well with all types of resin, as some are pretreated with something, beyond my knowledge.

    Fiberglass cloth you have is probably multiaxial, and i would have noe problem by stripping it up like that, but for stressed areas, I would buy woven cloth, a bit stronger.

    for butting; normally now people tend to go for epoxy, the main reason is that epoxy normally bonds better to wood surfaces, also is it more waterproof.

    As a general rule, I've learnt: you can use epoxy on top of polyester, not the other way. You will have to get the surface rubbed up, and degreased, to make it stick.

    Epoxy is pretty waterproof, vinylester is less waterproof, and polyester is not waterproof, kepp that in mind, as Plywood can take in water, expand and make the surface crack, increasing the speed of the problem..

    "Last" coat; I would go for some epoxy, to seal the surface, that will be both the inside bottom, and the outside bottom, or the complete outside.

    Window, you dont build a window, you buy it... A plexiglass piece (or whatever) And yes; If faired into level with the bottom,, preferably rounded edges, frame made water tight, window glued in with some Sikaflex (Polurethane(?) flexible rubberlike glue. Kids will love it. Keep it away from grounding or walking area or areas with curvature of the boat... Do not take away the protective plastic on other parts than where you will have the glue during construction...

    Good luck.

    Btw; there are pleeenty information here if you lurk around..:)
     
  3. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Yes, you could do that. But keep some things in mind:
    -if the cloth you have is woven cloth, it will work, but it will become very loose, so handle with care.
    -if the cloth you have is CSM (random orientated fibers) then it can only be used with polyester. More on polyester later.
    -if the cloth is multiaxial (orientated fibers, laying on top of each other, held togehter with stitching) then you are OK. If possible, have the fibers orientated in +/-45 direction. Makes for a stronger bond.

    Butting plywood is never a good idea. Try and scarf the joints. A 1:8 scarf ratio is good, a 1:12 ratio is even more desireable. Scarfed joints are the best option to joint plywood panels, especially in loaded areas. In interiors, you could get away with other methods (cutting a slot in the plywood, then inserting a small piece of thin plywood in, or by using lamellos, which is basicly the same principle)

    Above water level you could use a 1 part or preferable a 2 part polyurethane paint. If you are planning on keeping it transparent, use a PU paint with a good UV filter in it.

    If you are referring to epoxy resin: Yes, you can do that. However, keep in mind that you will always need at least 2 coats, to be OK. The first coat, try and apply not too much. No puddles, no shiny spots. The wood will soak up the resin, and a coarse surface will develop. (expanded wood fiber). After cure, sand flat with sandpaper, and now apply a second coat. When that has almost cured, apply a third coat. By applying it when the second coat is still tacky, you save yourself from sanding a second time.
    If you are referring to polyester resin, please do not be tempted to use that without fibers.

    Again, if fiberglass resin is polyester, then it is only suitable for glassing. If it is epoxy, make a sludgy mix of epoxy resin and some (cotton)fibers, and glue the gunwale to the side. Some screws or clamps will hold it in place during cure.

    There is no fiberglass resin. Please find out what they are referring to: Polyester resin or epoxy.
    Polyester resin and wood are not the best option. Adhesion is poor, and the resin is not so versatile as epoxy resin. (which can be used for laminating, glueing, coating and sometimes even casting (potting screws in oversize holes)).
    Polyester resin basicly is just for laminating.

    If you are unsure about certain things, invest your time in some research, and some testing. Make small scale test pieces of the constructions you are to face in the real thing. This way you generate some practice. And practice makes perfect...

    Could be done, but it is tricky to do. Make a recess in the bottom, and coat that with epoxy resin, just like the other parts of the boat. Make sure the recess is at least 8mm larger then the polycarbonate (lexan) panel (do not use plexiglass which is polyacrylate, and is brittle). Also make it at least 2mm deeper than the panel is thick. (use a thick panel, 8mm or so). Glue it in with PU putty (Sikaflex or similar) and you are good to go. Do not make the panel large, a 10x20cm panel is more than enough.
    However, first get yourself some confidence that the other structures of the boat are safe and sound, and that you can tackle the project. It is quite easy to build in afterwards, so it is not that big of a concern.
     
  4. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Plywood butt joints can be done and quite effectively, but you have to use epoxy and employ the "save a butt" method, which uses cloth on both sides of the joint. If the joint line is "plowed" out a bit with a grinder before the fabric is applied, it can be hump free when completed.

    Making an underwater port is a difficult thing. You must remember there's a lot of pressure involved and any joints, seams and seals will be tested. The successful versions of these ports have pretty highly engineered seals and gaskets.
     
  5. SPI-sail
    Joined: Jun 2008
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    Location: South Padre Island

    SPI-sail Total noob with a dream

    What epoxy to use? Where should I order from online and what brand and hardener should I get? I need something that doesnt require fiberglass cloth but will use that for the outside of hull.

    So far I both sides cut out, frame molds, and wood for the chine longs, but need the epoxy to butt the sides
     
  6. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Epoxy alone will not offer much more then a sealer coating on the exterior of the hull. Abrasion resistance comes from a fabric sheathing set in epoxy.

    All the major brands of epoxy have very similar physical properties. Though you can mix different brands of hardener, it's generally not recommended for the novice user, use the same brand and correct ratio hardener for your resin. Hardener type (speed) is temperature sensitive, depending on your building environment. Most permit on line shopping for their products.

    Do some reading, possibly at one of the epoxy manufacture sites. Most have a fair amount of "how to" information, which will be valuable in you first attempts.

    There is also quite a bit of information here about epoxy and it's use, so the search tool will be handy.
     

  7. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    And try and get a brand that is (more or less) readily available in your area.

    West System has some nice documentation, it is worth getting that to you (they also have a lot of info online). The info they give is basicly also applicable for other epoxy systems. The only thing that could be different is the mixing ratio. Always stick to the mixing ratio given by the manufacturer.
     
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