Strip plank foam core questions

Discussion in 'Fiberglass and Composite Boat Building' started by zstine, Aug 28, 2014.

  1. zstine
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    zstine Junior Member

    I'm researching building a strip plank foam core catamaran and have found numerous youtube vids (ex. link below) showing the strip planking on a female mold, as apposed to a standard wood lofted boat, typically over temporary male mold.
    1) what is the advantages/disadvantages of male vs female mold construction specific to foam core stip planked boats?

    2) The vacuum bagging process for these foam strip plank boats appears to use the foam strips as an air tight (mold) surface. With the foam strips all being epoxied to adjacent strips, there's a lot of seal area that could allow air into the bag. I would think the foam planking would not be a good air tight surface for bagging, but I see it done... Am I missing something?

    https://www.youtube.com/watch?v=RcCACPvHFlo

    Thanks,
    Zach
     
  2. susho
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    susho Composite builder

    Main advantage for a female mould is that you can do all the internals before demoulding, realising a stiffer shell which is less prone to deforming. Advantage for a male mould is that you can fair and paint the outside before turing it over.

    Second one: you can laminate a light cloth over the foam before the actual layup, pay a lot of attention while glueing, or fill up a groove in the foam with epoxy while glueing.
    Image from Fram:
    [​IMG]

    (Fram.nl)
     
  3. SukiSolo
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    SukiSolo Senior Member

    How many are you building? A one off is quicker on a male mould despite the need to finish the inside after turn over. For say 6+ it may be better to make a female, not forgetting you need a perfect finish male to create the female (or existing hull) in the first place. I would say production numbers decide this, the higher they are, the more sense in using a female mould layup.

    A one off on a male is easier finished in paint, whereas in a female you can use a gelcoat surface directly and build up from that, so prefinished. A lot of work for a one off, although you can flowcoat the hull(s) after moulding instead of painting. It just takes a lot of finishing time.
     
  4. DCockey
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    DCockey Senior Member

    Zach, the original poster, was referring to a set of female station molds for supporting the foam strips, not a female surface mold as used for fiberglass boats. Have a look at the video he provided the link to in the first post.
     
  5. SukiSolo
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    SukiSolo Senior Member

    Not forgetting, female moulds (polished resin), not frames are also used for building sheet ply (multi and single chine) boats as well. Yet to be convinced with the terminology of this type of foam core being 'strip plank'. More a mode of creating a former for the foam, so anything that allows the foam to retain shape whilst one layer(or more) of glass is vacuumed to one side.

    The OP's query about leaks in the vacuum, is surely resolved by using closed cell foam and ensuring the bag/poly sheet is not pierced. Susho describes a light tack/sealing cloth as one way of resolving this too.
    Hand layup can be used in conjunction with vacuum too instead of infusion, although a lot easier on much smaller projects - more of a reach and damage issue.

    Male moulds are not always temporary as the OP suggests. I have used virtually solid male moulds for cold moulding (veneer and strip plank) with and without vacuum. In fact, if you do use vacuum, you need the solidity to stop the form collapsing.
     
  6. DCockey
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    DCockey Senior Member

    The strip plank foam boats I'm familiar with have layers of glass on both sides of the foam.
     
  7. SukiSolo
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    SukiSolo Senior Member

    Glass each side is normal, but does not prevent one side being layed up prior to the other as per the build of the F39, as illustrated by Fram BV. The advantage doing it the way they have is by building the internal structure after the initial inner skin is formed, the 'hull' is now strong enough to take the vacuum load and resin infusion on the outer skin without collapse. No male formers are required as the internal bulkhead(s) etc are deemed enough.

    As for which way is 'better', female or male formers, it will still depend on the project, especially the scale. Still a fair bit of fairing and finishing to the outer skin if you use female formers for this type of build.

    If the OP were to give some idea of the size Catamaran required and the capability, it might be easier to point towards a narrower direction.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    Not sure what you mean by "vacuum load", but IMHO there's no load..
     
  9. groper
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    groper Senior Member

    depends on many things...

    Fairing of both sides is required either way - provided you want a light interior without liners and other rubbish weighting it down. A good catamaran (built in foam core no less) will have faired and painted surfaces inside and out. Dont think you can finish paint a hull that has not been glassed inside or turned over yet - possible perhaps, but highly risky, there is too much possibility of a slight movement, and thus you will require fairing and painting it a second time!

    Over a male forma, its easy and practical to layup the entire hull from gunnel to gunnel, whereas a female forma is usually split in half to allow easier access for working on it, rather than IN it... depending on the hull size and shape, its symmetry, and the type of workshop setup etc one method may be more practical than the other...

    End of the day, theres little major reason to say one method is more accurate, quicker, cheaper or otherwise better, than the other... they both work, and its more about the practicalities of doing the work, and how you would like to go about the work, more than anything else...
     
  10. zstine
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    zstine Junior Member

    Thanks for the comments. I'm in the education stage here, so there's no specific project, but I have 2 in mind. A high performance tri for daysailing, and a cruising catamaran to retire on 20 years from now.. which I better start working on so I can finish in time!

    I understand that female station molds allow the internal structure to be installed, but as SukiSolo said, you can leave in male bulkheads when strip planking over male stations. For me, male stations seem to be easier, smaller, cheaper to construct.

    susho gave a few good options to alleviate my concern of air getting through the core. I saw the F39 infusion and was impressed they didn't suck air through anywhere when there's literally a thousand linear feet of butt joint foam hand glued. susho's photo shows how those joints look.

    I do agree with TeddyDiver, there are no loads from vacuum bagging this way... atmospheric pressure on both sides of the foam/composite bag layup.

    If I move forward with the tri, I may use cylinder mold method. I'd probably build 3 identical 20ft amas off the same mold.

    Thanks again!
     
  11. SukiSolo
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    SukiSolo Senior Member

    All depends on where you put the vacuum bagging across the structure.....;)

    You can certainly arrange it so the whole thing (hull form) collapses or is neutral ie self enclosed. Both systems are used depending on application. TBH you won't need a lot of vacuum anyway, none of shapes are difficult.
     
  12. jorgepease
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    jorgepease Senior Member

    Take a look at Frams build, he used a female tool.... And Why strip plank, most core can be formed especially on larger hulls, will be a real PITA to fill between every plank. Also are you talking about infusing or bagging, don't see how you could move fast enough to do a vacuum bagging on an entire hull unless you have alot of help
     

  13. gonzo
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    gonzo Senior Member

    The advantage of a male mold is that if the bulkheads are located at a station, they are already lofted.
     
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