Mould/plug questions

Discussion in 'Boatbuilding' started by Ocboatdude, Mar 13, 2016.

  1. Ocboatdude
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    Ocboatdude Junior Member

    Well the shape of the boat has very easy curves to it. Or in other words no sharp curves. Think something like a kayak hull, but wider. I'm making something like that.

    And the mould I build will definitely have structural support to keep everything in line, and at an easy work height so I don't kill my back.

    I thought about using 1/4" luan wood for the plug because it bends very easily, and would bend at the curves I need to make. But I would have to use something over top of the wood before laying down the gelcoat for my mould or it would stick.. Any product out there I could use for the plugs finish layer that bends easily? This little kayak boat thing will have almost zero flat lines. Basically the bottom and deck curve
     
  2. Ocboatdude
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    Ocboatdude Junior Member

    This is a very simple drawing of what I'm looking at building...
     

    Attached Files:

  3. Ocboatdude
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    Ocboatdude Junior Member

    Sorry didn't think it would load sideways..... The blue is the deck, black is the hull
     
  4. gonzo
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    gonzo Senior Member

    Fiberglassing the plug is relatively easy, and it stabilizes the surface. One layer of 1.5oz mat is enough. Also, it is thick enough that you can sand off some material without cutting through.
     
  5. Rumars
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    Rumars Senior Member

    You can build the plug out of anything. Melamine is used on flat surfaces to minimize sanding.
    A step by step procedure would be:
    Build a boat upside down out of disposable materials. This can be a cnc cut EPS plug or something you build out of cheap wood, plywood, etc. It all depends on the shape of your boat and your skills. Maybe melamine faced chipboard will work, or maybe you have to strip plank the plug.
    The plug has to be capable to support the weight of the finished mold. Apply filler and sand. Repeat until you have a mirror surface. Filler can be anything that is sandable. Automotive fillers are often used. Now you have to assure that the polyester mold will not stick to your plug. Wax, pva, etc. Next is laminating the mold and reinforcing it in such a way that it will suport the weight of a boat inside without distorting its shape.

    The hard part, is deciding how to make the mold so that it can be taken of the plug (and the future boats from the mold). That means that you can not have the mold gripping the plug in such a way that it can not come off. Sometimes this means split molds or even a change of shape to your boat. It is something you do at the design stage and depends on the shape of the boat. For example a design with a lot of tumblehome will require careful mold planing and a simple V shape will not.

    Looking at your drawing I would strip plank the hull and deck, separate them and add joining details in foam.
     
  6. Ocboatdude
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    Ocboatdude Junior Member

    I'm getting all and more info than expected, thanks a lot guys!

    So I can build a skeleton and cover with 1/4" luan, and body filler to smooth out certain areas. Then cover the plug with 1.5oz mat, sand the mat smooth, apply the stages of wax and pva....... Then start my mould..... Does that sound acceptable?

    My design (hull and deck) shouldn't have any issues with the mold coming off of the plug, and shouldn't have any issues with production coming out of the mould.... As long as the wax and pva steps are followed, but as of design shouldn't be any issues.

    Rumors do you mind explaining the process of a strip plank plug and how to use foam to help the deck and hull join?
     
  7. Ocboatdude
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    Ocboatdude Junior Member

    I was in homedepot the other day looking at a material, it was about an 1/8" thick, very very flexible and very smooth.... I was thinking to myself "hmm I wonder if fiberglass would stick to that... Maybe it wouldn't with 10 stages of wax and coats of pva.....hmmm
     
  8. gonzo
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    gonzo Senior Member

  9. Ocboatdude
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    Ocboatdude Junior Member

    That's exactly what saw gonzo! Nice!

    What's your thoughts on using that stuff over top of the plywood on my plug? Do you think if I use that stuff, along with the costs of wax and pva, ill be able to gelcoat/glass a mould with no issues of it sticking?

    I think I'll have to try it out on a small piece.
     
  10. gonzo
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    gonzo Senior Member

    You could glue over the plywood and then laminate fiberglass tape over the seams. It will make the job of fairing much easier. The surface is reasonably flat, but does need some sanding to get it really smooth.
     
  11. Ocboatdude
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    Ocboatdude Junior Member

    Hmm not sure what to do yet... I think I need to buy a plug and mould building book

    I now understand how to build the plug and then the mould. But I don't understand how to make the plug smooth enough to then be able to add the moulds gelcoat. I don't know what materials to use overtop the plug.
     
  12. gonzo
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    gonzo Senior Member

    It takes a lot of of elbow grease and fairing with a long board. Then you sand with finer grits until you get to #1000 or so. After that it can be buffed/polished.
     
  13. SamSam
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    SamSam Senior Member

    This stuff works fine for plugs...
    http://www.homedepot.com/p/EUCATILE...d-Thrifty-White-Tile-Board-HDDPTW48/205995949
    It's not as flimsy as the fiberglass stuff and the surface only needs wax to laminate on. Exposed edges need to be sealed and waxed and PVA'd. If the humidity is constant and with enough support it will keep it's shape well without becoming wavy.

    [​IMG]

    This is a developable surface

    [​IMG]
    [​IMG]
    these surfaces have compound curves

    [​IMG]

    sheet materials , like plywood or melamine, can't do compound curves.

    Your hull drawing is of a shape that is not developable, as narrowing the ends to make a boat shape would turn it into a compound curve.

    If you made it with multiple chines, that would then be a developable surface, as it would be a series of one dimensional bends that would closely resemble your desired shape.

    [​IMG]

    Your deck drawing (as it is drawn) presents a number of problems. It's all compound curves, so no sheet materials could be used to make the plug. A mold for that deck would have to be a multiple piece mold, otherwise the piece would not be able to be removed from the mold as it would be locked in. The rolled edges are a nuisance to laminate unless there is easy access to them, meaning you don't have to reach into something and do it by feel, without being able to see what you're doing, or you have to stick your head in there a laminate a few inches away from your eyes.
     
  14. TANSL
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    TANSL Senior Member

    It seems clear that Ocboatdude not only needs to know the differences between a plug and a mold but many other aspects of building hulls with molds. I think here, slowly, with the positive support of we all, he can learn, at least, that he has to learn many things before going to build anything.
     

  15. Ocboatdude
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    Ocboatdude Junior Member

    Samsam thank you for explaining that to me

    And thanks guys for taking the time to talk with me. I definitely understand I need to learn more than just the difference between plug vs mould. Any books or videos you recommend I purchase to help me build one? Now I have past experience with glassing, but I've only used 2,4,6,8,10 oz cloth. I've never used 1.5, or 2 oz mat. So the next step is figuring out how much cloth to use and what kind, also don't want the thing to be real heavy. I have something similar to what I want to build and the glass measure just about a 1/4" thick. But right now I'm still focused on how to exactly build the plug then mould

    I'll draw up w better idea of what I'm thinking about building later today when I have the chance
     
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