Fast Build Scale Model

Discussion in 'Projects & Proposals' started by rwatson, Dec 11, 2011.

  1. rwatson
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    rwatson Senior Member

    making good progress on a 1:5 scale model for a Trailer-Sailer.

    Pictures at

    http://schoolroad.weebly.com/model-development.html

    I have found that making sheets of Fibreglass and VynilEster, mounting them inside a 'basket', and glueing them with Epoxy is working out well.

    The compound curved bottom has to be strip-planked, but mounting the planks dry, and tabbing them in place with Epoxy and glass strands seems to work well.
     

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  2. Doug Lord
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    Doug Lord Flight Ready

    Model

    Great job! Did you lay up the glass sheets on glass or another smooth surface? That ought to save a bunch of sanding...
    Is this a boat you're considering building?
     
  3. Chuck Losness
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    Chuck Losness Senior Member

    I know that you are just building a model but I have thought of using this method to build a hard chine fiberglass boat. Probably my next dinghy. I have always wondered if the fiberglass panels would bend like a sheet of plywood. Curious as to your experience with your model.
     
  4. DGreenwood
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    DGreenwood Senior Member

    Interesting approach. I'm curious about the aluminum channels on your jig?
     
  5. BATAAN
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    BATAAN Senior Member

    Some builders of large powerboats use this method.
     
  6. rwatson
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    rwatson Senior Member

    re the panels - yes, I laid 6oz cloth and a thin layer of chopped mat on a waxed melamine board, with peelply over the top.

    On one version, I laid Mylar down first, as the waxing gave me mixed results. Then I laid peelply and heavy plywood on top to squash the wrinkles in the thin Mylar.

    I can see that a vacuum pump would be the way to go for large panels, or maybe even a layer of plastic with upturned edges to pour two inches of water as weight.

    The aluminium channels gave me a very true straight edge to align the forms, and fitted into the slots in the cnc cut moulds for maximum accuracy. Its very hard to machine small widths of timber really accurately, and fasten things to them without splitting.

    Originally, this model was to build a large boat from. But I took so long building it that the NA came up with an improved hull in the meantime, so this may end up being a 'Mark 1' version to make sure the 'Mark 2' really is better.

    Design details at http://schoolroad.weebly.com/project-2.html
     
  7. rwatson
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    rwatson Senior Member

    Yes, it works like a charm. For large boats, you generally use a layer of high density foam as well as fibreglass to give you a nice self fairing bend. You then do a layup inside the hull for final rigidity.

    Derek Kelsall http://kelsall.com/UniqueKSS/KSSMethod.htm has been building hulls like this for years. Its only the cost that put me off doing that for this project.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    RW, I've made panels before and used window glass as the mold. I waxed with partall# 2 and then(for a small pannel) poured PVA over the mold with a receptacle under the mold so as not to waste the stuff. If done in a very clean , dust free room the gloss is extraordinary-as good or better than the best wax. The PVA is water soluble and you just wash it off the part and there is no wax residue left on the part.
     
  9. Willallison
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    Willallison Senior Member

    Looking good RW!
    I'll post a pic of Graphite's mold frames when I get a chance... the two look remarkably similar...
    BTW, who did you get to do your design work in the end?
     
  10. DGreenwood
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    DGreenwood Senior Member

    I suspected that is what you were up to. It gives me a great idea for aligning full sized molds.
     
  11. JRD
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    JRD Senior Member

    RW, I like your approach here. I have seen a number of negative comments in the past about difficulties in getting a cage mold like this fair, but there do seem to be a number of benefits;
    -having more ridgidity in the shell when it comes to filling and fairing the hull exterior
    -being able to set up more of the interior framing while the hull is still in the mold means that it's pretty solid already when you flip it.

    Only question is one of trusting your design data and set up skills enough to go right through the build without sighting the external lines :(

    Do you plan to follow the model with the real thing in short order?

    Looks like a slippery shape underwater. I'll be watching your progress with interest.
     
  12. tunnels

    tunnels Previous Member

    You could make sheets of glass almost the exact size you need with just a very small amount of trimming to be done . All sheets can be made on a bench with a smooth semi shiny surface so have nice finishe one side (Outside )you can even mould in a recess for the glass for the joining tape The joining tape is best to use 600 gram triaxle tape 150mm wide !! Can be got in rolls this can also be used to tape the joins inside as well but i would prefer to use 600 gram tri axle glass ( 90/45/45 ) is the best tape as all 3 layers are working acress the joins . Make your panels for dinghy 2 x 450 gram chopped strand matt with 600 gram triaxle (90/45/45 ) and 2x 450 gram chopped strand matt for all the hull panels using polyeser of vinvylester resin ! wont be to heavy but robust and quite durable . Can glass all the joins with good epoxy and all the attaching bits you want to add seats and wooden gunwhale 2 inside and one outside with a rebate torebate join and glass sandwiched between completely cover the top edge of the glass panels ,transom packer for outboard ,bow blocks etc etc .just like building a stich and tape ply wood boat but instead of ply make glass panels !!. If you make thin patterns you can make you panels almost exactly to the correct size so theres almost no waste just 10mm round the very outside . Its just 2 of each for the side and 2 for the bottom . Advantage of glass is has no grain so get a even nice bend and no hard spots . :p:D
     
  13. rwatson
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    rwatson Senior Member

    I am interested in this approach - but not sure what PVA is known as commercially. The wax residue is a bummer.

    Is is a glue ?
     
  14. rwatson
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    rwatson Senior Member

    Thats the plan. There are a few projects on these forums that have used the technique.

    Its always a problem, but even on an inverted mould, the lines arent always easy to eyeball accurately on a big hull. Its all about measurement.

    These frames were CNC cut, and mounted on straight rails -so I hope the computer got it right.

    That was the plan originally, but this design may not get built .. see below.

    Yes, I would like to see those. This design was by an NA that doesn't wanted to be associated with the design, as it against his design philosophy, and he slipped out of the project 2 years ago, after supplying Cad lines of the hull.

    I was very happy with the shape, and found a keen engineer to do the scantlings, in Lithuania.

    He was able to contribute a lot of great ideas and calculations, and has now come up with an even more suitable hull design - which I am planning to also build a model of.

    The downfall of the current design is that we suspect it would be very slow under sail, running before the wind, with a lot of the transom buried in the water.

    I'm not able to put the new design on the net yet, as it is still under development, and we haven't formalised the commercial arrangements on the new design. Its a radically innovative design, but unproven.
     

  15. Doug Lord
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    Doug Lord Flight Ready

    ---------------
    RW, "PVA" is polyvinyl alcohol used in combination with Partall #2 wax. It is a green liquid that is water soluable so you simply wash it off the part. You can spray it, but on small parts pouring works infinitely better if you set it up right in a clean room. It prevents any wax residue on a finished part.
    One of the things you can do is use Partall and PVA on the mold, then spray in a primer and lay up the epoxy right on the primer so when you pull the part it's ready to paint. On small(30") models I built I sometimes sprayed the paint in first(like gelcoat) and then laid up right on the paint(much lighter than gel coat for racing models). I used a simple Krylon enamel and Imron(polyurethane) depending on the boat. You have to test the paint and/or primer with your epoxy first. Epoxy paints didn't seem to work.

    Here is the info on both products:
     

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