Hydrofoil Manufacture

Discussion in 'Boatbuilding' started by sacko200, Jan 30, 2012.

  1. sacko200
    Joined: Jan 2012
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    sacko200 New Member


    This is my first post on these forums! I am currently involved in a project to design and make a high speed human powered boat. We have the overall concept decided after around 2 months of research. The Hull has been purchased and is an aquanaut hv kayak.

    The main design features 2 hydrofoils, one at the stern giving large lift and bow mounted hydrofil giving stability and height control. The kayak is powered by two people pedalling with a tandem recumbent bicycle transmission which has a vertical shaft running down a fairing attached to the stern hydrofil. A propeller will be mounted to the stern hydrfoil.

    I have experience in mechanical design and analysis but very little manufacturing experience and I was hoping someone here could help.

    We have access to air extracted rooms and almost any machine tool that would be required. We were thinking of an epoxy resin fibreglass hydrofoil, but would this be able to be made into the complex shape of the rear hydrfoil? It has to contain the horiztonal drive shaft for the propeller as well as bearings? We have a budget of around £300 for the two hydrfoils.

    Thanks in advance for any help anyone ccan give,

  2. BPL
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    BPL Senior Member

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  3. Submarine Tom

    Submarine Tom Previous Member


    Pictures will get the conversation rolling remarkably quickly.
  4. Doug Lord
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    Doug Lord Flight Ready

  5. Herman
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    Herman Senior Member

    300 GBP leaves very little in terms of failure, but also to hire someone to make you one. Your first attempt should be spot on.

    Basicly the way to produce foil shaped parts is to have a top and bottom mould, made from CNC-ed plugs (I hope you have access to that).

    The plugs can be MDF, after CNCing and sanding, apply epoxy and PU paint.

    Make quite rigid moulds from that. See if you can source some cheap glass. Use epoxy for the moulds, so CSM glass cannot be used.

    Now it is time to make the real thing. I suggest a reasonable amount of UD, and some biaxial +/-45 for the foils. First apply some epoxy in the mould, let it cure into a tacky state. Laminate your fibers in. Do both sides. Fill the moulds with epoxy foam (Sicomin) and close up. Pour most of the foam in the thin part of the profile.

    After cure (needs inmould postcuring, find a large oven) release, clean up and fill air pockets if needed.

    Good luck!
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  6. jehardiman
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    jehardiman Senior Member

    How big are the foils?... I'm guessing less than 2m span by 15cm cord? If so, then there are some tricks we borrowed from model aircraft to make foils for other HPV's.
  7. Petros
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    Petros Senior Member

    The strongest lightest foils would come out of molds as described above, but there is a moldless method used by home built aircraft builders. You use a heated wire on foam blanks to cut out the foil shape (you make plywood end templates to guild the wire), than hand lay-up over the core. You have to subtract the composite build-up thickness from the templates to get the foil shape you want. This only works for straight foils segments, but you do not have to build a mold and can get very accurate shapes without much tooling.

    Go search for forums or blogs for people building Rutan's Vari-ez or Long-ez aircraft and you will find pictures of the set-up.
  8. Submarine Tom

    Submarine Tom Previous Member

    Right again Petros.

    They can be curved somewhat after cutting, before glassing.
  9. Doug Lord
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    Doug Lord Flight Ready

  10. hospadar
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    hospadar Junior Member

    Might also want to look into surfboard building techniques, this is how they do it. Start with a foam blank, shape it with hand tools (generally planers and surform, you could probably CNC the foam blanks if you have the tools/skills so you can get a super accurate foil shape), then vacuum-bag (or just do a hand lay-up) the fiberglass onto the foam.

  11. Herman
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    Herman Senior Member

    Hydrofoils usually are too thin to perform this technique. I guess the thickness will not be much more than 12mm or so.
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