Print through from foam edges?

Discussion in 'Fiberglass and Composite Boat Building' started by DennisRB, Jan 22, 2014.

  1. SamSam
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    SamSam Senior Member

    I don't think the lines are caused by fenders. In the third photo the lines go all the way aft, way past where fenders would be, plus there's nothing back there to hang a fender from. The lines also evenly cover the whole area back there, which fenders don't do.

    It doesn't seem to be a very tough boat, but if the foam is so fragile that fenders at the dock crush it, well, what's the sense in having a boat that delicate and flimsy?

    Is that (the lines) the only reason the boat is priced cheap?
     
  2. DennisRB
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    DennisRB Senior Member

    No the boat needs a paint job (not related to the print though) and has stuffed engines, which I am fine with as I am willing to take care of this. That is why its going cheap. However I am not fine with structural issues. The experienced owner builder was fine with having thinner laminates for a lighter boat. I guess the next owner may not have been as good at docking etc. For the average cruiser a thicker laminate on the hull sides would certainly have made more sense. But the average cruiser does no try to hit 24K as lloyd tells me was the top speed they got out of it back in the day.

    The lines are not everywhere. Mainly in the location I took pics off.
     
  3. redreuben
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    redreuben redreuben

    I have built strip cedar hulls with 600gms DB on the outside and west epoxy, after 18 months, print through. As mentioned contour core (the little blocks on scrim) will too, balsa will.
    Ply bulkheads without landings on a foam hull can print through.
    In a moulded product the glass weave pattern from woven rovings will print through, especially when it cures a bit hot.
    Its all about different shrink/expansion rates of the various materials and densities.
    Structurally it means little except that you have a thin skin so use with this in mind.
    Adding glass may well be the only way to hide this permanently.
    If you fair out the ripples and repaint it is my opinion they will come back, fainter maybe, and over a longer time but with a minimal skin they will come back.
    What makes me curious is their orientation, horizontal, seems an odd way to plank a boat in foam ?
    Also they don't seem to be evenly parallel, I'm wondering if the boat was built in sheet foam and rather than heat the foam to take the shape they just put in some slashes with a blade which have consequently filled with resin. A bit odd methinks !
    RR
     
  4. DennisRB
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    DennisRB Senior Member

    I have seen print though on cedar strip hulls very often. I guess this is because there are just more cedar strip boats. Also I wonder if as the wood ages it distorts which shows up the planks?
     
  5. TeddyDiver
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    TeddyDiver Gollywobbler

    That's foam strips as wooden strip planking.. nothing odd with that.

    The only way hide print through with epoxy laminate is after curing and fairing done after that, dunno if that's the case with VE too but reckon so.
    In the OP's case the after curing has most likely happened with time and sun but no fairing has been done.
     
  6. DennisRB
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    DennisRB Senior Member

    I guess that is why Lloyd said these days post curing prevents this prob. This boat was faired then allowed to post cure in the years after its completion. Another reason why Epoxy is the best.
     
  7. redreuben
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    redreuben redreuben

    Well I would disagree, waste of labour, on a long thin hull like a catamaran vertical or angled strips would have made way more sense.
     
  8. Steve W
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    Steve W Senior Member

    You need to post cure epoxy just the same, whatever resin you use it shrinks at a different rate to the foam/cedar/balsa/whatever core so you need to get the shrinkage out of the way before fairing. We built a cedar core/west epoxy boat years ago where the customer wanted it painted black, so we painted it and pushed it outside for a few months, it looked terrible with the gloss of awlgrip but then we longboarded it and painted it again, it all came out within the paint and primer.

    Steve.
     
  9. ondarvr
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    ondarvr Senior Member

    I’m not going to comment on whether it was built strong enough, or if there is any internal damage, only on the surface profile.

    There is nothing unusual about the surface profile on the hull side, although it is more pronounced than what you would typically see. Vinyl Ester, especially older versions, tended not to cure well in thinner laminates, they are rather sluggish and can have a great deal of post cure, so while strong, they didn’t always look the best after a while. Newer VE’s that are designed to be used in thin laminates perform much better cosmetically than the older versions.

    It also depends on how they cut the core and bed it, if not cut correctly you will end up with a resin rich area at the edges which will cure and shrink at a much different rate than other areas, this almost always prints through and can be easily seen on the surface.
     
  10. DennisRB
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    DennisRB Senior Member

    Thanks guys. I thought epoxy was more stable and had less shrinkage than VE?
     
  11. TeddyDiver
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    TeddyDiver Gollywobbler

    It's not so much shrinkage, just bit soft especially at higher temperatures and then it happens. That's close to the temp when the postcuring happens and makes the print permanent..
     

  12. waikikin
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    waikikin Senior Member

    Back in the day, one off Crowther foam sandwich boats were often planked vertically with full width sheets.
    One thing I'm seeing there especially in those shots from the port quarter is that the lines kinda "interleave" past each other........... I'm wondering if the core got kerfed in situ to help it sit & backscrew or tie back to the batten mold. I assisted in foaming up a No.85 in 30mm Divinicell & we had to kerf the core but did the inside to carefully placed "development lines.
    The lines printing on that boat look quite wide like a kerf filled with resin/balloon mix, without xray vision or simply being allowed to sand back to glass what's there is a guess.
    Looks like a great boat.
    Jeff.
     
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