How are fiberglass plug made with complex curves?

Discussion in 'Fiberglass and Composite Boat Building' started by dylondylondylon, Feb 1, 2014.

  1. dylondylondylon
    Joined: Oct 2013
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    dylondylondylon Junior Member

    Hi, I am knew to the forum, but have been poking around for awhile because of my own interest in boat building. I am interested in fiberglass boat design and am curious how the plugs work for boats with complex curves. For example, the Chris Craft Carina has a curved back making it hard to lift straight out.
    This Chris Craft no seam
    [​IMG]
    where this Frauscher has a seam to achieve the curved rear.
    [​IMG]
    This aquariva seamingly (sorry ha) has no seam and yet is concave and not totally vertical.
    [​IMG]
    Do they pull it forward, or is this a two piece mold. If anyone has any pictures of two peice molds or of the process it would be helpful. In addition, if there are two piece molds made how is there not a imperfection in the hull? Thank you!
     
  2. Westfield 11
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    Westfield 11 Senior Member

    There is an imperfection from where the halves join called a molding line. Use extra gelcoat in that area so that when you grind the ridge away you can just polish it afterwards.
     
  3. gonzo
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    gonzo Senior Member

    Molds can have many parts. If they are well matched with the seam waxed and polished, it should not show a line. You can find books of mold making for casting and ceramics. The techniques are the same regardless of material.
     
  4. redreuben
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    redreuben redreuben

    As mentioned a complex mould usually has joins with the matching flanges having male/female locators to align the sections.
    I would suggest however that the boats pictured may have been released by lifting the bow first and drawing the part forwards.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd have thought it wouldn't have released from a one piece mould, not for me anyway. :D
     
  6. redreuben
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    redreuben redreuben

    The hull is at its thickest in the midsections, so, release the hull and draw it forwards as you lift the bow up.
    But you have to raise one eyebrow and poke your tongue into your left cheek as you do it ;)
     
  7. mselle
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    mselle Transportation Designer

  8. SukiSolo
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    SukiSolo Senior Member

    There are a lot of fibreglass/composite kit and fully manufactured cars around. Plenty of split lines with those!.
     
  9. garrybull
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    garrybull Senior Member

    this is my hull mould i recently built.

    to get the boat out you have to pull the transom of first , then the sides of the mould and then the tunnel section of the mould pulls downwards.

    the mould is in 5 pieces with the tunnel in 2 pieces but that stays bolted together.

    i made the tunnel in 2 pieces so its easier to man handle.

    if you look at the flanges you will see the male and female locators.

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  10. dylondylondylon
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    dylondylondylon Junior Member

    Wow, thanks for the help. All great info and pictorials.

    Redrueben, I found a ChrisCraft factory tour video, and you were right. They pull the boat up and forward to pop it out. I supposed that when engineering a mold they calculate the tolerances needed to lift it out easily.

    Garrybull, thanks for you the step by step. That is a fantastic illustration of your mold. What kind of plug did you use to achieve a mold like that? CNC or wooden plug? If you built it yourself it certainly is impressive to get the fittings and female/male locking mechanisms.
     
  11. dylondylondylon
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    dylondylondylon Junior Member

    thanks mselle, that resource is very useful to see the multiple mold process.
     
  12. garrybull
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    garrybull Senior Member

    yes i made it all myself.

    i used a hull mould which i already had which is a 3 piece mould.

    i built a melamine tunnel and bolted it in between the outer hull sections and then added a melamine transom panel.

    then it was all waxed and polished and a coat of pva put on.

    then gelled up and layed up a fibreglass hull.

    i then raised up the sides of the new hull etc.

    turned it over and did any repairs and painted it with duratec surface primer and wet flat it down and polished it up.

    after that i put on the flanges for the new mould and built the mould up a section at a time.

    the locators are made out of 30mm nylon turned down on a lathe to have a chamfer on them.

    they are then screwed to the flange and gelled over when making the mould.

    its taken me a few months to get to where i am now but im loving every minute of it.

    i have just made the wheelhouse plug which im hoping to paint later thisd week.
     
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  13. mselle
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    mselle Transportation Designer

    Why don't share the source. It's probably interesting for a lot of people.

    M.
     
  14. Herman
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    Herman Senior Member


  15. dylondylondylon
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    dylondylondylon Junior Member

    Yup, thats the video. Kind of hard to tell, but you can see they lift it up and forward.
     
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