Foam cores !! fore and against !! time to share info again !!

Discussion in 'Fiberglass and Composite Boat Building' started by tunnels, Jul 6, 2010.

  1. tunnels

    tunnels Previous Member

    I remember the first time i saw foam core way back in the 1970s i wondered what sort of advantages it had over the Balsa we always used .
    Didnt take to long and there as a wave of differant types and densities ! and it got a little bewildering ,then differant patterns of cuts and slices for lots of differant applications and uses . the list just kept growing over the years along with the problems that reared there heads , the biggest and badest was called "CORE SHEAR". :confused:
    First time i heard anything about this was on a big launch that the bottom had sheared and come loose in big areas . Have seen some horrendous examples here over the years and all very frightening .:eek:
    Like all things all materials have there uses and they have limitations .
    I think its time to share the good if there is any !!The bad i bet theres quite a few AND the ugly ones where its self distructed and been a total write off .:mad:
    Good place to share the does and donts as far as sticking cores to the skins also . wet glass and if so how much and what kind of resin . Or core bonds in there various forms . In the begining we made our own from a formular written on the wall that was really faded with time . never bagged anything just pressed it all by hand or walked on it if it was possible !!. :D
     
  2. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    Oh, no, Core-Wars...

    -1. Many people talk about "solid laminate" where they mean single skin. Is a cored laminate not solid?

    -2. When engineered right, and installed right, a core will not give you any problems. But if people still believe they can guesstimate core thickness and properties on their napkin at dinner, and install by splashing it in a wet layer of glass, then walk over it, and think they do fine, then they can expect problems for sure.

    I might react more extensively in the future, or I might not.
     
  3. jonr
    Joined: Sep 2008
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    Location: Great Lakes

    jonr Senior Member

    What about fiber strands that run through the foam, perpendicular to the normal fibers to help prevent separation of the outside layers? Does it work?
     
  4. tunnels

    tunnels Previous Member

    Solid glass is just that !! Glass only ! No core but more on that later !

    The phrase single skin is also very miss leading . single to me means one skin (layer of glass ) and thats not practical at all .

    Core thicknesses used in some cases has been hit and miss and a little miss understood . Thickness goes hand in hand with the density that should be used and also the amount of internal framing ( bulkheads,stringers , girders, grid frames etc etc ) and eventually the panel size that is created at the end of the day.

    So much of laying cores is up to the guys doing the job and how good they understand the job at hand ,precutting fitting and laying . Every part of the whole operation is important reguardless of whats used to hold it in place !

    :D :p
     
  5. tunnels

    tunnels Previous Member

    Yes its a really good idea , it is to asist the holding together of the top and bottom glass layers and makes perfect sense. :idea:
    In the case of extreme conditions core shear is always and has always been the majoy worry. :mad:
    I have never used any of these cores but yes it definitly has its place for sure and i am surprised its taken so long to find its way on to the market place . :D
     
  6. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    That is because the price is not compatible. It is quite a process to stitch the foam. I have it available in PU and in PE foam, both not really suitable for boats.

    One must also bear in mind that the complete strain will be transferred by the strands, not by the foam anymore.

    For calculating the skins and core thickness of a boat, one needs to know quite some variables. Nowadays ISO 12215 gives nice guidelines.

    Panel size, type of boat, loads, are all input variables.
     
  7. apex1

    apex1 Guest

     
  8. CatBuilder

    CatBuilder Previous Member

    Ok, I won't pretend to be a NA or true designer here, but I will drop in some anecdotal evidence. Take it for what it's worth:

    I've been on the water for a long time. I've owned cored boats all along (balsa) until I bought a Catalac catamaran that was solid (layers of) glass.

    While shopping for the Catalac, I was in South Florida where there were scores of catamarans for sale. I boarded so many my head was spinning.

    What I found was that just about every (9 of 10?) foam cored *production* catamaran was failing in some way or another... mostly deck delamination, some hull delamination. The only foam cored boat I boarded that didn't have an problem at all with delamination was a Kellsall catamaran built in South America (with care, I assume).

    The evidence is there - foam falls apart.

    However, the foam that was falling apart could have been from the owners of the production cats opening up the core or from the builders of the production cats doing a lousy job. I imagine it's a little of both. I found it very interesting that the custom cat (Kellsall) had no issues and was like a rock. Either it was built well or the owners knew not to compromise the core... maybe both!

    This is just a little anecdotal evidence I have seen. I can't say for sure why the production boats were all falling apart at the core/glass join, but they were.

    Incidentally, none of my balsa cored boats ever had a problem with delamination. Also, my Catalac's balsa deck only had one small spot where there was delamination because someone whacked it into something. It was popped loose by impact. It seems (on the surface from observation only) that balsa holds up better than foam, though I have nothing to prove this. It's a "gut feeling" from experience rather than anything empirical. Boat for boat, I have seen more foam falling apart in my time than balsa, including several boats I've been on that I haven't owned, including monohulls as well.

    Back to the more intelligent discussion! :)
     
  9. tunnels

    tunnels Previous Member

     
  10. apex1

    apex1 Guest

     
  11. tunnels

    tunnels Previous Member

     
  12. apex1

    apex1 Guest

    Come back to topic mate!
    Foam cores! The next field you have no clue about.......................

    YOU are not interesting, it is the novice seeking info here who counts.

    Not the novice telling old salts why water cooks.
     
  13. tunnels

    tunnels Previous Member

     
  14. tunnels

    tunnels Previous Member

    Foam unlike balsa comes in a range of densities and types but there is a big differance in the prices as well and i a high percentages of cases this is the factor that determines what foam gets used and gives it a dad reputation . Balsa has hard and soft within its make up . To softer density foams are dangerous to use any where . i cant understand what its even made for .
    Again !!! 80% of failures are from poor workmanship and 20% from wrong choice of materials for the job . so in combination you havent got much of a chance !!
     

  15. Herman
    Joined: Oct 2004
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    Location: The Netherlands

    Herman Senior Member

    I think this is true for every boat or structure, but many high volume boatbuilders are not following the rules or advise from core manufacturers, primarily to save cost.

    First of all, pressing scrimmed foam into a wet layer of glass is definately NOT the way to go. I do not care for the argument "we do it for severl years" or "everyone does it".
    Even worse is that the kerfs are not filled with resin at all, and an inner laminate is squased on top. job done, get the inner structure in, and cover with topcoat. Looks nice, so it sells.

    A core, when hand laminating, should be bedded in corebond, the kerfs filled, and a vacuum applied. depending on the corebond, the foam should be hot-coated. And all nicely within the time frame of the resin setting, please.

    This will ensure a very good bond between the laminate and the core, and the kerfs filled. If the choice for the core was good (usually needs a NA to determine) and the laminates are good, then you will end up with a perfect boat.

    2 small anecdotes from that:

    I once received some panels from a medium volume, high prized and highly regarded boatbuilder. I will not reveil the name, but let's call it "builder X" which seems more than appropiate. These panels were cutouts from the windows in the hull (not a good idea either, I would go back to single skin with a reinforced outer skin, but ok, it can be done like that). I was ordered to do an osmosis test on the outer skin. However, the thickest panel I can insert into the machine, is 10mm, so the core and the inner skin had to go. This boat was built with ATC Core-Cell, so I expected a very tough job, separating the skins. Surprise surprise, the outer skin came of within seconds, the Corebond was very brittle, and there was a patch of "neverbond" of about 80% of the panel. This was the actual boat!!!

    Second anecdote: One of my clients had a boat which had integrated tanks, which were known to have been done in a sloppy way. As the interior was being adapted, it was decided to redo the tanks and piping, and a new through hull connection was made. The yard owner took a hole saw, and started drilling about 4 meters away from the blackwater tank.... The "water" was splashing everywhere, the kerfs in the foam were not filled with resin, but with black water. He probed the hull in several places, and about everywhere there was black water.
    The boat was declared a total loss...

    ----
    These above problems make it that I do like resin infusion for in-mould cored construction. Although you will need to run some simple tests to make sure you infuse both laminates well, that DOES outweigh the trouble of doing a good core installation by hand.

    Foam core over building frames is another matter, but that is a slightly other subject, I am sure I will ventilate my opinion on that. (in short: outside by hand, inside infusion, unless the outer laminate is very thick)

    I do hope this reply gets the topic back on track.
     
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