Glassing over foam core questions.

Discussion in 'Materials' started by Jonathan hintzman, Apr 19, 2018.

  1. Jonathan hintzman
    Joined: Apr 2018
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    Location: Seattle

    Jonathan hintzman New Member

    I am designing a small hydrofoil and would like to know from the communities perspective the potential benefits and downfalls of my design and method of construction. My plan is to design the hull in rhino and then machine it out of a ridgid foam and glass over the entire structure. I plan to reinforce stress points and add strength by cutting the machined foam core and adding ribs but I want to leave most of the foam in place. 1 benefit I can see is having a continuous fiberglass Hull with no seams and no form to build.
    The basic concept of the boat is a tandem sea kayak with 2 small outriggers forward, self adjusting t-foils. What do you think?
     
  2. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum.
    Good luck with the design. There are many here who will gladly assist your use of Rhino.

    Your proposed build technique will result in a heavy craft. You describe a single fiberglass skin over a foam form. In this sinerio, the fiberglass must be very thick because the foam is non+structural. Strong lightweight boats can utilize FG-foam-FG sandwich construction. The two thin FG skins interact with each other and the foamcreating a rigid structure.
     
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    You haven't offered any idea of scale, but monocoque hulls are fairly commonplace. As Blueknarr points out, there is glass on both sides, though. It sounds as if your ribs are planned as insets. Ribs would not generally be needed if you glass both sides. Thus it seems the ribs are not a good idea. If you inset them, the foam would be weak at the inset as the core thickness varies. A tandem sea kayak would not require outriggers as each kayak is essentially an outrigger to the other kayak.

    Rigid foam is fine as a construction material; despite it being unpopular with boat builders. It has its place as a low cost option. I built two outriggers for a canoe with rigid foam; encased them in light glass and epoxy and they are a superb lightweight, durable product with epoxy.

    Your method, however, needs some tweaking. And I have never tried to shape something as large as a kayak. I don't quite understand how you expect to achieve fair lines without some type of form. Nor do I see it practical to machine the inside of the structure if the foam block is solid to start. If you machine the foam in sections; you would still need to glue them together somehow and make sure the CL and WL remain true. The foam would also need to be rather thick in order to achieve stability without glass at the start in a formless build and the thicker glass would require a larger kayak for the same space on the inside.

    Hope this helps with the 'project'.
     
  4. Blueknarr
    Joined: Aug 2017
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    Location: Colorado

    Blueknarr Senior Member

    Much more information is needed before anyone could intelligently comment on your design concepts.

    Back to foamcore

    Multitudes of one off boats have successfully used foam panels flexed to a jig for their primary construction technique.

    I don't have enough information about your project to give definitive advice. Consider the following:
    Pre-glassing one side of foam panels
    Set panels in female jig glass inward
    Tab seams
    Remove from jig
    Shape exterior
    Glass, fair, paint
     
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  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Yes
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    It seems, you're self designing a "hydrofoil", whatever you may mean by this, which has some obvious questions in itself and also self engineering this puppy, with little understanding about the material properties and methods in either approuch. Have I got this about right? How far from shore can you swim back too? Composite and sandwich core structures have to be fairly well engineered or bad results will likely occur, so maybe a little dimensioning needs to be applied, before any reasonable answers should or could be offered. We can offer the "Cliff's Note's" version of common methods and solutions, but do these logically apply to your "hydrofoil". Simply put, how about enough detail in the project that someone can actually get an idea of what you're up to, besides a single sentence of something that out of hand sounds "draggy", at the very least, particularly for a foil borne craft.
     

  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I think that before even discussing about the structure, the big question is how does the OP intend to generate enough thrust with a paddle to get a catamaran kayak up on plane.
     
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