Needed - inexpensive core material

Discussion in 'Boat Design' started by Martell_Florida, Jul 10, 2007.

  1. Martell_Florida
    Joined: Oct 2005
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    Martell_Florida Junior Member

    Hello all,
    There is a lot of great information around here and I need some advice.

    I need a lightweight core material to be used in a "sandwich" construction for a deck. I know all of the expensive "Name Brands" and I was hoping to find a less expensive alternative. Wood is too heavy, so a closed cell foam of some sort would be the way to go. any ideas, and where to purchase near Tampa, Fl would be great.

  2. KnottyBuoyz
    Joined: Jul 2006
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    KnottyBuoyz Provocateur & Raconteur

    lightweight+foamcore=expensive at least that's all I've ever been able to figure out. Want inexpensive? Balsa or marineply maybe but not the lightest option. How big a project might be the next question. Trying to deck 1000 sq. ft. ain't no small undertaking but if you're decking a 12' dink, well that's doable.
  3. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Vee section frames on a grid, maybe using plastic drywall corner bead. They cost a doller apiece or so, epoxy will adhere to them, they are glued in place easily using masking tape and dots of epoxy, remove the tape, FG tape over (hopefully you've chosed the wide radius corner bead).
    Raggi will love this method, just wait and see. it will make your deck stiffer than a cored deck, and very light.

  4. RatliffFranklin

    RatliffFranklin Previous Member

    Core Material

    Insulation Styrofoam.

    You can pick it up in big sheets at Home Depot.

    Just make sure you use an epoxy resin. Polyester resins will dissolve it.
  5. catsketcher
    Joined: Mar 2006
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    catsketcher Senior Member

    Be Careful

    When you add the money for the glass and resin I think it would be very silly to use a cheap core for a deck. Decks get very high impact loadings from feet and heels, they have lots of holes drilled in them for fittings and get thumped by winch handles and more. I would urge extreme caution against using cores like extruded polystyrene in high load areas. You will end up with a very expensive throw away part. Foam has to be have a high shear strength. Cheap foams don't.

    A case in point. When I was building my 38ft cat a friend told me I could save $2000 by using construction plywood rather than marine ply. I used the marine ply. When he came to sell his boat he had to do huge amounts of interior work to hide the inferior ply and then drop the price about $30 000 compared to similar boats. That $2000 cost him about $40 000 all up.

    If you are building a throw away canoe then it may be fine to go super cheap. If you want to go offshore or sell the boat to recoup costs then do what others do - ply with framing, polyester with PVC foam, glass with stiffeners or the designed lay up.

    Your time and the money you spend on the rest of the project should not be compromised by a small portion.


    Phil Thompson
  6. SailDesign
    Joined: Jan 2003
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    SailDesign Old Phart! Stay upwind..

    This is like asking for a budget-priced Rolls-Royce. If you want the benefits of an expensive material, you have to buy the stuff. Period.
    Having done with the negative aspects, let's try to lighten the mood - have you asked around local boatyards to see if anyone has some less-fashionable foam lying around in the stockroom? Something like 5lb Airex is pretty much not used any more, since it doesn't sand well. If you are willing to pour the sweat into sanding (if it is needed at all), you will have a deck with one of the best deck cores out there. Just remember to use a heavier core in way of fittings and tube the screw-holes. :)
  7. alan white
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    alan white Senior Member

    I would say that any practical yacht, one that is not exclusively raced, could stand the miniscule difference between an expensive and labor intensive cored deck and a marine plywood deck properly framed. If light weight is wanted for all-out performance, the cored deck is lighter than ply. Practical considerations like where to put the windlass are meaningless. I hear so much about the "lightest material", but the lightest materials for their weight are almost always impractical and subject to puncturing.
    If money is tight, an uncored deck with some well engineered foam-cored frames skinned with glass would make sense.
    I had a balsa cored deck once, and it was improperly done at the factory, The holes (all 200 of them) were not jacketed or reinforced with plywood.
    In fixing it, I cored every hole, and added ply plates under cleats and attachments.
    I thought about it, and realized that while the cored deck was light, it was also completely dependant on many many small details all being done correctly.
    I would rather have had a ply substrate skinned with epoxy. I think manufacturers have gone to coring more because it fits with their tooling and methods, and impresses buyers more. Plenty of balsa and foam cored decks out there with heavy anchors and windlasses and paraphinalia on top of them.
    The owner can brag about his technologically correct and efficient construction, while his deck actually has 3 times as much weight attached to it than the actual deck weighs. Then he wants to attach a new winch, and its a huge deal. He can't just drill and put in a backer. He has to do complicated surgery (at least he'll pay a good deal more to have it done).
    Coring is fine if well done, but as said, it's the ease of doing so in a production situation that is promoting its use on cruising yachts. There is a gain in lightness, which is fine, but the home builder might do better to save his time and money and go with plywood, epoxy/cloth, and inside frames.
    If he wants a racer, then by all means go to whatever extent necessary, but otherwise, it seems to make little sense.

  8. Raggi_Thor
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    Raggi_Thor Nav.arch/Designer/Builder

    I am not sure I get it :)
    But if it's cnc cut I am in!
  9. messabout
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    messabout Senior Member

    I'm looking at a test panel consisting of half inch Klegecell and vacuum bagged epoxy glass skins. The skin is sufficiently thick to stand reasonable abuse. The finished panel is 0.640" overall thickness. Weight 1.44 pounds per square foot. 12 mm Okume ply with an 8 ounce GRE top sheathing is just a tad lighter than the foam cored panel. Way easier to work with and will cost less too. Okume can be gotten from Quality Plywood in Clearwater or try Dave Lucas boatyard in Bradenton. Klegecell or balsa core stock from Fiberglass Coatings in St. Pete.

    Alan is right about the miniscule difference in weight of ply vs foam sandwich.
  10. Martell_Florida
    Joined: Oct 2005
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    Martell_Florida Junior Member

    Thank You!

    You have all provided some great insight and given me lots to think about. I must say, I am more confused now than before, but I feel comfortable with my options at this point. I will have more questions soon, so don't go to far.

  11. alexlebrit
    Joined: Aug 2006
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    alexlebrit Senior Member

    If it's a small deck area I recently found some "cheap" foam which seems to fit the high sheer strength need too. It's actually foam for use under laminate floorings. It is however very thin, I think about 3mm but doesn't seem too err floppy, if that makes sense. I've been using it to make the deck and hull of a large 5 metre touring kayak/human powered boat, and it's worked well for that.
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