One off fiberglass boat built off of plug?

Discussion in 'Fiberglass and Composite Boat Building' started by itchyglass, Aug 27, 2022.

  1. itchyglass
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    itchyglass Junior Member

    In terms of building a fiberglass boat... can one be built straight off of the plug? Obviously that will mean a ton of sanding and fairing in order to achieve a nice finish. However is that done? Or could there be issues releasing off the plug, flipping and installing stringers?

    Boat size being 15 feet.
     
  2. comfisherman
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    comfisherman Senior Member

    You mean can the plug be used as a finished boat? Or can a mold be made so fair without a plug?
     
  3. itchyglass
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    itchyglass Junior Member

    What I mean is that traditionally, you build the plug, and then make a mold from the plug. Can you lay up the hull directly onto the plug, pull it off, flip and finish. Much more finishing work...
     
  4. Rumars
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    Rumars Senior Member

    Yes, it's a common technique for one off builds. If the hull is to flimsy without interior reinforcements you build some removable outside support wich conforms to the hull and keep it's shape while finishing the interior.
     
  5. itchyglass
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    itchyglass Junior Member

    I suspect at 15 feet it may hold shape ok. But certainly some removable outside supports would be helpful
     
  6. comfisherman
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    comfisherman Senior Member

    Yeah it's just a lot of fairing. With modern CNC I've seen guys make molds with super accurate patterns that they faired out and then went straight to work building boats out of.
     
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  7. itchyglass
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    itchyglass Junior Member

    I have seen those massive cnc's and they are impressive. I have cut a small 10' skiff from styrofoam before (cut as 20 separate pieces glued together) on my smaller machine... but it was more of a "surfboard" type build... very light layup and I was not chasing down a perfect finish.

    Does anybody know of any build examples straight from a plug? I have been searching but nothing yet!
     
  8. comfisherman
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    comfisherman Senior Member

    I guess I was referencing CNC cut plywood for forms to make the plug. Although I did see one of the big ones in the Washington area that cut foam that was sprayed onto wood jigs and it was really impressive. Sadly 10 years ago it was almost 125 dollars a square foot for a single-use mold from the CNC flat deck.

    I did a cursory swing to see if the boat was in the harbor right now on my way to the hardware store. Guy here is a heck of a Craftsman he built a top house that had quite a bit of curve and complexity to it by making a female mold straight from plans with a jig that had been cut on a CNC table. I think it would have been a little nerve-racking to have 10 grand worth of materials in the hopes that it would turn out perfect.... but it did. I'm trying to remember to grab a pic but they're not in right now.
     
  9. fallguy
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    fallguy Senior Member

    Make a female plug?
     
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  10. Rumars
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    Rumars Senior Member

    It's doable even in the most primitive conditions. But, as fallguy said, you can also do a female plug, aka. "direct female molding".

     
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  11. jehardiman
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    jehardiman Senior Member

    I've seen people build one on the beach using wet sand and plastic sheeting for a male plug, female part. If you really don't care about the FINISH...and are only interested in the UTILITY, then almost anything can be used for a male plug.

    Edit, maybe we need some terms. For me a 'male' plug sticks out and produces a 'female' part...i.e. moulded to the inside. A 'female' mould goes in and produces a 'male' part...i.e. moulded to the outside. Most production FRP boats are produced with 'female' moulds by "two 'guys' and a Binks gun".
     
  12. jehardiman
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    jehardiman Senior Member

    Sorry I Edited the above post to make sure I stated what was in my mind.
     
  13. waikikin
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    waikikin Senior Member

    Itchy,

    Plenty of larger boats- Mconahy yachts building maxies in this fashion but would put loads of labour onto fairing. More common now to go one off female moulding- check out Inovation Composites to facebook for a couple 40' yachts in that fashion, also Jon Sayer built some nice yacht that way.
    Jeff.
     
  14. mudsailor
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    mudsailor Junior Member

    It’s how pretty much every IOR one off race boat in the 70’s and 80’s was built (and that was a lot) ……it’s also easier to lay glass and foam over a convex surface rather than into a concave surface. How much fairing was dependent on builder skill and attention to detail.
     

  15. wet feet
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    wet feet Senior Member

    That can be a very effective technique,but also a lot of work,but then getting a presentable boat is always a lot of work.It can be a great deal easier if the intended hull is a hard chine form and has developable panels.Such a happy set of circumstances makes it possible to build a female mould from melamine faced panels and the outer surface will be about 95% finished when the hull is released.There will still be some comparatively minor finishing work to do_Obviously this would be totally dependent on the hull panels being developable and if they are a modern design program may well provide panel outlines.It is a lot easier with the use of CNC cut female sections that incorporate the material thickness but a conscientious traditional lofting will get you there-with sore knees.

    For a round bilge type of hull you have the option of a male form covered with strip planking and if the construction method is directed to the use of foam,you can get away with quite large gaps.The foam may need to be applied in the form of "planking" and can be secured to the form by fishing line-which is quite easy to cut free when glassing the inside.I don't know if C-flex is still in use as it was quite adaptable but still labour intensive.I don't know too many people who endure a second dose of fairing and finishing a male moulded hull unless they are professionals in the business of making one off racing boats.

    My sole encounter with a female CNC machined hull mould was as an observer,at a safe distance.The surface was nice,but the designer had clearly never spent time in a moulding environment as it took a lot of improvising with ratchet straps and props to get the two halves to align and remain in place.There were no reference lines on the outside of the mould for waterlines or stations and it made locating the initial stiffeners challenging for the poor devils doing the work.None of which means that the technique can't work.It can work and work well if the process is thought through properly,it won't be cheap and you could probably buy three near new similar boats for the same cost.

    There seems to be a typo that I can't readily edit-apologies.
     
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