One off fiberglass boat built off of plug?

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

  1. TANSL
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    TANSL Senior Member

  2. tpenfield
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    tpenfield Senior Member

    Perhaps on a small boat, as mentioned the 'plug' could be used as a 'male mold'. The challenge as I see it will be that the initial hull (fiberglass) thickness will have to be fairly thin in order to release the hull from the mold and without the benefit of having any internal structure added while in the mold.

    The net result will be a fairly flimsy shell of a hull, which then you will need to go about completing. So, you will be challenged with bracing the hull, making it 'true' (i.e. square, level, symmetrical), while you go about the process of adding thickness and structure to the hull. Then you will need/want to make the outer surface smooth, gelcoated, etc.

    I am not sure that will provide any benefit vs. making a female mold from the plug.

    The only way that it may work out is IF (if) the male plug is also acting as the core of the hull ( netting a result similar to Boston Whaler hull construction). Then you would be glassing both the outside and inside of the core/plug.
     
  3. fallguy
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    fallguy Senior Member

    Of course, this is the beauty of the female plug. You can add stiffeners before removal, and all exterior finish work is done after removal from the plug/jig.
     
  4. itchyglass
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    itchyglass Junior Member

    Why would you envision it would be more difficult to release from a male plug instead of a female plug?
     
  5. tpenfield
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    tpenfield Senior Member

    Experience in getting parts to release from molds . . . not much but some.
     
  6. mudsailor
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    mudsailor Junior Member

    Resin shrinks…..so on a female mold it pulls away from the mold, on a male mold it shrinks tighter onto the mold
     
  7. itchyglass
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    itchyglass Junior Member

    Ah ok, that makes perfect sense. Would it be more difficult or just straight up impossible?
     
  8. wet feet
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    wet feet Senior Member

    It certainly wouldn't be impossible,after all lots of components have recesses that were released from a male element of a mould.The basic principle of having sufficient draft always applies.If all else fails you can always demolish the temporary mould in any case.
     
  9. tpenfield
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    tpenfield Senior Member

    Hard for others to say since we have not seen the mold and do not know how much fiberglass you plan on laying up . . . even then, who knows :rolleyes:. You will have to use your judgement, factoring in the advice you have received here and elsewhere.
     
  10. itchyglass
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    itchyglass Junior Member

    Correct! However wouldn't it be no different than laying up the mold from the plug? Is there often times problems with female molds shrinking around the plug? Maybe there is a major difference in making a mold off the plug vs making a hull off a plug...
     
  11. tpenfield
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    tpenfield Senior Member

    Try it and let us know. (some pictures would be good to see)

    Lots of variables to consider, many relating to how well the plug is shaped and coated for releasing. One difference that I can think of is that when you are making a female mold from a plug, you have the opportunity (really a necessity) to add stiffeners and bracing to the outside of the mold before releasing, which probably helps.

    When releasing a hull from a male mold, it is just the 'shell' of the hull. The process certainly can be done, it is just a matter of what you feel comfortable with as to your skills of releasing the hull from the mold and finishing the hull from the shell.
     

  12. redreuben
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    redreuben redreuben

    Without any description of the hull shape or intended use this is a ridiculously open ended question so .........
    If its a power boat style with flat surfaces build a female mold in gloss formica covered sheet material like ply or mdf.
    If its a round bilge style you can go male or female with a frame and stringer mold and foam sandwich or, strip plank it in foam, cedar or my favourite Kiri (paulownia)
     
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