Weight of hand laid fiberglass/epoxy?

Discussion in 'Fiberglass and Composite Boat Building' started by Crocodile69, Apr 9, 2014.

  1. Crocodile69
    Joined: Feb 2014
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    Location: Key West

    Crocodile69 Junior Member

    Hey all,

    I recently bought a 34' sailboat (GRP hull) here in the Florida Keys and every piece of exterior wood on the vessel has completely rotted away (bowsprit, boomkin, cockpit coaming boxes, hand rails, life raft cradle, etc).

    When the vessel first came to south Florida 3 years ago from New England the exterior wood was pristine at the time. Most of it was either mahogany or douglas fir.

    Living in the sub-tropics, I have never been a fan of wood on boats...if you're not continuously paying attention to it either the sun, rain, termites or wood worms will usually destroy it for you. And because I don't relish the thought of constantly tending to the wood every month, I've decided to cast and replace everything in fiberglass.

    My question is does anyone know the approximate weight of hand laid fiberglass (using West System epoxy resin)? I'm looking for weight by the board foot 12"x12"x1". I know there are many variables, whether all the air is out, type of cloth used, amount of resin used, etc... so I'm just looking for a good approximate idea. Not looking for weight of poly resin as I know this is lighter than epoxy.

    Also not looking for the weight of G10 boards as their vacuum seal/pressing process obviously creates a denser, heavier material. Comparing G10 to African Mahogany, for one board foot the G10 weighs in at 8.98 lbs while the mahogany is at 2.67 lbs, but again, I'm not using G10. Creating my own glass/epoxy boards should be lighter just not as strong as G10...or as expensive.

    I understand that replacing all the exterior wood with fiberglass will be adding more weight than the wood. I'm just trying to figure out approximately how much more weight. I found a conversion here: http://en.allexperts.com/q/Composite-Materials-2430/fiberglass-1.htm ...but I just became more confused the more I read it.

    There are obviously areas where I could use Core cell or Divinycell foam sandwiched in epoxy glass, though I will not be using this method for the bowsprit, boomkin and other structural aspects of the vessel…in those areas I prefer the stronger solid glass layup.

    Any idea?
     
  2. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    A "board foot"of glass laminate is going to be around 7lbs assuming a 40% fiber fraction, you would be doing well to achieve this in a wet lam. I don't see any reason why you would want to use epoxy for something like this, polyester would be more than adequate as would csm. Have you considered using coosa board coated with epoxy and painted, it has a density similar to wood, about 2lb / BF. There may be a suitable plastic available in sheet form such as phenolic impregnated canvas like they used to make block sheaves and cheeks out of years ago, the stuff lasted forever and it could be painted, or it could perhaps be varnished. Another material worth doing some tests on would be the stuff they make house decks out of, cheap to buy at the lumber yard in wood like dimensions, easy to work like wood, and possibly paintable with proper prep. The biggest thing to watch for with plastics is thermal expansion, some like PE can expand a significant amount in the long dimention making it impractical to use.

    Steve.
     
  3. Crocodile69
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    Location: Key West

    Crocodile69 Junior Member

    Thanks for the info Steve.

    I've looked into PE sheets, but as you said, the thermal expansion/contraction almost makes it useless for my purposes. I've also contacted several of those plastic lumber deck companies, like Azek, though they tell me their product is not good enough for use on boats. I see their lumber used for marina decks throughout the Keys here, so you would think it would be able to take a beating from the sun and moisture.

    I've never considered phenolic impregnated canvas, looks like a good candidate...though I would imagine the weight is similar to that of G10?

    I am not opposed to using polyester, it's just that a slow cured epoxy has just always been easier for me to work with in these hot/humid temperatures. Would you know the approximate weight of poly per board foot? I hear it's lighter than epoxy, though not sure by how much.

    Thanks again.
     
  4. Crocodile69
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    Crocodile69 Junior Member

    Been looking into the approximate weight of poly wet lam vs. epoxy...looks to be only about a pound lighter at most.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Epoxy laminates are lighter then polyester and vinylester laminates.
     
  6. Crocodile69
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    Crocodile69 Junior Member

    cured poly lighter than epoxy?

    I've read that before use both epoxy and poly resins are approximately the same weight, though as poly cures it evaporates styrene vapors (that awful smell) making the cured state ultimately lighter (and because of this less waterproof). Some say poly is a little lighter while others say it is vastly lighter than epoxy. Anyone have any info to back this up?

    Thanks in advance.
     
  7. foxy
    Joined: Aug 2009
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    foxy Junior Member

    Whether its polyester or epoxy, the weights vary between products. Most resins fall in the range of 1.10 to 1.22 specific gravity or 9.2 to 10.2 lb/gal depending on the formulation. You need to to check the technical data sheet for the resin you are planning to use. You can download these from the manufacturer's websites.

    Keep in mind that many resins designed for open molding use fillers to increase the viscosity and it is the fillers make the resin lighter and easier for water vapor to migrate through. Infusion resins tend not to be filled and have a chemical thix agent that increases the viscosity after some time has elapsed. That allows the resin to flow easily into the laminate and then thicken so that it does not drain out before it cures.

    The amount of styrene that evaporates is related to the process. Sprayed laminates loose up to 30% of the styrene, hand laminating with buckets and rollers loose 10-12% and with closed molding the loss is less than 5%.
     
  8. Steve W
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    Steve W Senior Member

    Not so, if the laminate schedule is the same, a hand layup using pe/ve will be a little lighter.

    Steve.
     
  9. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Not so, if the laminate schedule is the same, a hand layup using pe/ve will be a little lighter.

    Steve.
     
  10. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Your correct Steve, but it's rare for the schedule to be the same between the laminate approaches. The reason most hand layups are heavier in polyester and vinylester are the bulking fabrics used in these schedules unlike epoxy, which typically don't employ these comparatively resin rich fabrics.
     

  11. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Par, by bulking fabrics I assume you mean the practice of interlaying csm between layers of WR, i quit doing that when low profile stitched fabrics became available 30 odd years ago. With heavy woven rovings it was necessary with polyester because roving to roving had very little contact area, this is not the case with low profile fabrics and it is completely uneccesary to use mat with VE although i realize that many still do. It really isn't even necessary with PE.

    Steve.
     
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