Another idea for making hulls

Discussion in 'Boat Design' started by HCB66, Jun 24, 2018.

  1. HCB66
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    HCB66 Junior Member

    I'm wondering if something like the kind of sand they use to pour metal or maybe modeling clay or even concrete could be sculpted into a hull shape, covered with plastic and then fiberglassed over. Take the resulting fiberglass hull off the sculpted mold and add the stringers etc. It's a way to get the precise shape you want without fighting stubborn materials to get them into it.
     
  2. upchurchmr
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    upchurchmr Senior Member

    Try it on a small boat.
    Typically you press the sand with a lots of force to form the shape of the mold for casting metal.
    A boat of any size will require a huge amount of pressure to make a shape that is not very durable (in sand) for doing the laminating of glass over.
    TNSTAAFL.

    There is no such thing as a free lunch.
     
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  3. Skyak
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    Skyak Senior Member

    I won't say you can't, but I will say there are many ways it could fail and the slimmest of chances that it will be superior to current methods using foam core.

    How do you get the "precise shape" into the sand?

    Well to answer my own question, the largest "3D printer" I ever saw works by spitting polymer into successive thin layers of fine sand. I think this is it (the VX4000) but what I saw was in Germany; Industrial 3D printer | voxeljet solutions https://www.voxeljet.com/
    My plan was to make patterns for cast iron roto-molds or blow molds -it knocks tens of thousands of dollars out of the tool cost but the mold machines are still costly and slow. For my designs, vacuum forming will do -and faster.
     
  4. messabout
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    messabout Senior Member

    ^ TNSTAAFL.............. Them's words of wisdom Upchurch.

    Credit the OP with a capacity for inventive thinking. No that method would not be a practical one. I encourage you to keep thinking HCB66
     
  5. upchurchmr
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    upchurchmr Senior Member

    Do you know the cost for a 3D printer of that size?
    Do you have any idea of the weight of a cast iron roto-mold, or how you would make such, and how much it would cost?
    How fast would you have to spin a rotomold and how big of a motor would it require?

    First though - why rotomold? That is for polyethelene plastic, not a sand cast tool.
    Have you ever seen how delicate a hydraulically compressed sand casting tool is? It chips easily and has to be handled delicately.

    Last time I was associated (not directly responsible) with cast aluminum tools for rotomold, it was so expensive that an aerospace company decided not to pursue the project - in spite of the huge cost they are willing to pay for structure.

    I'll give credit for the initial steps of an idea. Now comes the real work. Filling out the details, evaluating the cost and viability of the idea.
    Don't give up, just do the work. Or get the education to allow you to do the work.
    And tell us more details as you develop them. Old farts can be shortsighted, non creative, and blind to good ideas.
    Young, or younger guys are usually the ones who make strides in Engineering advances.
     
  6. rwatson
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    rwatson Senior Member

    From experience, trying to make a "precise" shape out of something like clay or sand, is really, really hard. And then to get it hard enough to put press other material onto it, is a whole new world of pain.

    There's nothing "stubborn" about wood or plywood for shaping, it the ideal medium of strength and accuracy.

    The "problem" of making hull shapes using conventional means is all in your head, and with a little bit of practice, you will understand why the most commonly used methods work the best. Try it - you will like it :)
     
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  7. Mr Efficiency
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    Mr Efficiency Senior Member

    How did those metal hulls made by digging a boat-shape depression in the ground, placing a large continuous sheet of metal in or over it, and setting off an amount of explosives, go ? Probably lost popularity in an age of terrorism jitters.
     
  8. ondarvr
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    ondarvr Senior Member

    EPS foam is about the easiest way to get a shape and is relatively low in cost, it can be CNC cut or shaped by hand, this allows for complex shapes with simple tools.
     
  9. HCB66
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    HCB66 Junior Member

    Sand is one idea, clay is another, of course either one would be a one shot deal once the hull was removed you'd have to redo a lot of it to make the shape again assuming it was possible to form over it. Concrete is reusable over and over but if your hull got stuck you couldn't just dig the material out from under neath it. Plywood obviously can do the job as well. I don't know if you have to form the glass over the plywood and you end up stuck with plywood inside your fiberglass hull or if you can remove the fiber glass from the plywood mold. From what I've seen, it looks like sometimes the mold is made and the fiberglass is put on the inside of it and removed after drying. It's the same concept except in the case of my idea the mold would sit up side down on the ground like some sort of sculpture of an overturned boat hull. I think it has an advantage in that you have gravity on your side, the fiberglass would tend to hang over the shape and more naturally form to it. Epoxy could be painted and troweled over the top, worked into the fiberglass in the usual way. I imagine there are release agents available or maybe you could put a sheet of plastic between the fiber glass and the concrete to make it easy to remove.
     
  10. rwatson
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    rwatson Senior Member

    Neither of those methods is ever used without carefully cutting out molds and arranging them in the correct distance and sequence either.
     
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  11. rwatson
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    rwatson Senior Member

    The concept of "hanging " fibreglass is a non starter.
    If you try that, it deforms on cure, but most likely shreds apart and falls to the ground during wetout.
    Glass only sticks to plywood frames if you don't take the easy precautions of applying release film of some sort.

    This "make the shape " concept is also a non -starter. Will the "shape" be symmetrical, seaworthy ( or even just lakeworthy), will it be efficient under whatever powers the craft, will it hold the amount of weight, and without listing.

    If you don't carefully design and shape the hull, it will be a useless "blob" that has only aesthetic value.

    Honestly, its not that hard to acquire the skills to do a decent job. Start on something small, and tear your mind away from solving problems by making bigger problems.
     
  12. gonzo
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    gonzo Senior Member

    Casting sand could be made to work. However, you first need to make a pattern to press into the sand to make the shape. It would me much cheaper, easier and effective to simply use the pattern (plug) and make a standard type of mold.
     
  13. Skyak
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    Skyak Senior Member

    Up, I don't know the cost of the 3D print machine and never cared. At the time it was not for sale, just run as a service. Like you, I was just an engineer at an interested company -not even directly responsible. For my own interest it was just a new way to cut the tooling cost of rotomolding or blow molding-which has good economics for durable small boats. I have no interest in buying or building the machinery, but they are common enough I am confident that I can find someone to run it at a fair price. You seem to misunderstand the plan.

    3D print ->metal casting->production mold

    I moved on but I didn't find any reason it could not work.

    I am sympathetic to your comments about the forum overlooking engineering advances -despite my being old and as flatulent as any. Check out the 3D printing open source projects. They solve problems faster than you can think of problems.
     
  14. HCB66
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    HCB66 Junior Member

    We need to remember that it is innovation that drives things forward, not doing the same thing over and over.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    It's a lonely business being an innovator.
     
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