Spotted gum and fg hull extension.

Discussion in 'Materials' started by d. right, Jan 6, 2018.

  1. d. right
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    d. right Junior Member

    Hi mate, I do a lot of night runs out to the local reefs here, in our wet season a lot of debris gets washed out into the ocean, talking about 20 ft logs here, think solid timber take a hit better than foam. I do know the americans are big users of foam and balsa cores but I am not a big fan of that stuff. Also not aware of current aussie build practice with cores either.
     
  2. d. right
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    d. right Junior Member

    Thanks Par, I might do a test panel with epoxy and s/ gum. One straight up and one with solvent treated s/ gum.
     
  3. rwatson
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    rwatson Senior Member

    Salt water does inhibit spores, but not forever. Poly is not waterproof, so as Par says, it tends to hold the water in the timber for months after a "timber only" boat would have dried out. This is bad enough from a weight perspective, but up there in your warm environment, the rot will get established. The whole idea of timber is to provide some strength, but if its being eaten away, you might get a nasty surprise in a few years.

    Regarding high density foam as "exotic" is probably a bit over conservative. It is true that it offers only incompressibility , and the resistance to sheer and tension forces have to be supplied by the glass weave. I would hope the prices up there aren't too out of reach, and the ease of working and material savings might make it the preferred solution.
     
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  4. PAR
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    PAR Yacht Designer/Builder

    Peel strength of a coating or sheathing will be problematic if you don't "clean" out the oils first, but worthy a test, as you'll be like the rest of us and learn to invent new, creative curses, in no time. epoxy coatings, especially with a sheathing are time tested (several decades now), but anyone that's repaired production boats can tell you how polyester holds up on wood in a wet environment.
     
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  5. d. right
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    d. right Junior Member

    65 now, not many new curses to learn now lol. Will go with epoxy over 20 mm marine ply.
    Thanks.
     
  6. d. right
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    d. right Junior Member

    Have laminated aussie hardwood benchtops with this stuff before, Bostik AV515. Might laminate 10mm marine ply either side of s/gum and that will allow use of polyester encapsulation. Data sheet approves for marine use.
     
  7. rwatson
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    rwatson Senior Member

    You can't go wrong with Bostik.

    It sound like you are planning to rely on the strength of the bearers, which is probably not necessary if you do the glass correctly, and spread the stress out over the whole structure.
     
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  8. PAR
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    PAR Yacht Designer/Builder

    There's no such thing as polyester encapsulation, just polyester covering before the moisture content rises enough to get rot started. Polyester isn't water proof, just moisture resistant. If this (polyester) is combined with a contact coat (10 mills of gelcoat), then it's fairly waterproof. How much are you going to save using polyester? You'll need bulking fabrics, unlike epoxy. You'll need a thicker laminate for similar strength to epoxy, using more materials and yes, epoxy does cost a little more, but what are you really saving, once you count up the additional fabrics and labor to make a polyester laminate similar to an epoxy laminate? Look into "BoteCoat" epoxy as the better and much more cost effective alternative to the major brands.
     
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  9. rwatson
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    rwatson Senior Member

    Why the unwillingness to use Epoxy Mr D ?? It can't be cost so much. It wets out easier, is easier to mix the ratio's correctly, is actually waterproof, is stronger .....
     
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  10. d. right
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    d. right Junior Member

    Epoxy is twice the price , I just have to get my head around the dollars. Even restored to new condition its still an old boat and would not be worth much.
    Thanks, D Right
     
  11. rwatson
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    rwatson Senior Member

    BoteCote and West Systems are expensive if you don't buy a truckload. What you want is the industrial brand Epoxy Resin and Hardener R180, which claims not to be a marine epoxy, but all the commercial boat builders have used for years.

    Its about 2/3rds the price of West Systems or Botecote Epoxy ( eg. EPOXY RESIN R180 1KG at Harbourside Chandlery http://www.harboursidechandlery.com.au/catalog/epoxy-resin-r180-p-6553.html ), but if you hunt around your area, you might get a better price.

    The other saver idea, is that there is nothing wrong with building the actual extension module out of Polyester ( like a tub on a ute) but then Epoxying the module and the beams together. Its only the Wood you are trying to protect.

    Worst Case - coat the timber in three layers of epoxy with a light layer of glass fabric, and let it cure, BEFORE you apply the Polyester. The grip the Polyester has on the Epoxy will be as good as it will ever have on the bare wood, but your wood will be waterproof.

    Finally, don't fall for the old wives tale of "thinning " either Epoxy or Polyester to "soak" into the timber, for better adhesion. All you get is structurally poor, brittle resin against the wood, to admit water even faster as it breaks down over time.

    For the ultimate cheapest job, Plaster of Paris will give you a good looking result, but I wouldn't put the boat in water until the new owners cheque has cleared.
     
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  12. d. right
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    d. right Junior Member

    Haha, might go plaster of paris hilton.
     
  13. PAR
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    PAR Yacht Designer/Builder

    BoteCoat is about 45 (AU) a liter, how does FGI compare (60 AU)? West System is about 47 (AU) a liter.
     
  14. rwatson
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    rwatson Senior Member

    I don't know where you got the FGI $60 price from? No-one buys 1 litre hobby packs. That link I posted had FGI at $30 per litre ( including hardener) for the 24 kilo pack. That link was for full retail, and I DID say he should be able to get it at a better price locally.
     
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  15. d. right
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    d. right Junior Member

    20 litre pack in Cairns $445
     
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