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Thread: Polyester resin for plywood boat build

  1. #36
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    Default Re: Polyester resin for plywood boat build

    Thanks, I'm looking forward to getting going as well. Yeah well its been unusually hot, high 20's and low 30's here for the last few weeks too, but its rained all summer for the last few years, so yeah rain is the norm.
    I'm looking at 4hp up to maybe 9hp, plus an electric trolling motor. I'v designed in plenty of reinforcement to take the loading forward along the gunwales, and I have braced them laterally to accept the load without spreading. The tolerances I am using to calculate the forces are from a 25hp engine on a plank built timber boat, so they are way over spec. but rather that than swimming away from a pile of floating debris.
    The weight is going up proportionally with the reinforcements so I'm expecting it to be heavy. A few willing guys can lift onto a pontoon in the harbour here but not every day, so I'm accounting for it being left in the water, and pulled out on a trailer periodically.
    I will update in the coming weeks.

    Thanks, and all the best

    Thats the plan anyway.
    Quote Originally Posted by Hugh MacD View Post
    Looking forward to seeing pics Dylan I understand about the humidity problem on Erin (although last time we went over there we came back sunburned!?!) as we live in the Northwest of the US...very similar climate. You mentioned a motor? What power range and how heavy? That will considerably affect your strength requirements. You also mentioned a steep ramp requiring a 4X4 for launching, but you might consider that if the boat's light enough, you could easily carry it to the trailer (OK...with a couple of chums...beer's cheaper than a 4X4). Food for thought

  2. #37
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    Default

    A thought about your proposal to use epoxy resin and woven roving: the binder that holds the roving may not dissolve and allow the roving to conform to shape. As far as I know, woven roving is only suitable for use with polyester resin or vinylester resin.


    Kevin


    Sent from my iPhone using Tapatalk Pro
    There are two kinds of boaters: those who have run aground, and those who lie about it.

  3. #38
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    Default Re: Polyester resin for plywood boat build

    Quote Originally Posted by Breakaway View Post
    A thought about your proposal to use epoxy resin and woven roving: the binder that holds the roving may not dissolve and allow the roving to conform to shape. As far as I know, woven roving is only suitable for use with polyester resin or vinylester resin.


    Kevin


    Sent from my iPhone using Tapatalk Pro
    Dylan - I don't think anyone has mentioned 'the bible' yet. That is "The Gougeon Brothers On Boat Construction". It's available in book form, or as a free download - along with a bunch of other epoxy/boatbuilding instructional material - from West Systems.

    I suggest you get it. It'll clear up a lot of misconceptions, and guide you well --

    https://www.westsystem.com/instruction-2/
    David G
    Harbor Woodworks
    http://www.harborwoodworking.com/boat.html

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  4. #39
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    Default Re: Polyester resin for plywood boat build

    reading it at the moment.

    Very comprehensive.

    Thanks

  5. #40
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    Default Re: Polyester resin for plywood boat build

    Dylan - I don't think anyone has mentioned 'the bible' yet. That is "The Gougeon Brothers On Boat Construction"
    I did, way back in post #11.

    the binder that holds the roving may not dissolve and allow the roving to conform to shape. As far as I know, woven roving is only suitable for use with polyester resin or vinylester resin.
    I can't recall ever needing to saturate woven roving fabric with epoxy, but I have used a lot of individual strands pulled from hunks of roving for various reinforcements and saturated them with epoxy resin without a problem. These tended to be strange things like replacing torn-out sections of cross-country ski edges with small, unidirectional bundles of the yarns, or making transparent and bombproof fillets for things like bulkheads or float tanks using bigger bundles of the yarns. Glass mat certainly has binder problems when you try to use it with epoxy, but I'm not so sure about roving. It seems to resist mostly because the yarn bundles on typical 24 oz. roving are so big that it makes the cloth stiff and quite resistant to bending around any sort of sharp curves.

    Perhaps he meant fiberglass cloth, rather than roving, because nobody in their right mind would stick roving on the outside of a hull where it would need to be filled to get it smooth. It would take a tremendous amount of resin or bog to do so, adding a lot of excess weight, cost and labor involved, while reducing your glass to resin ratio and ending up with a brittle surface.

  6. #41
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    Default Re: Polyester resin for plywood boat build

    Roving:
    While there is rarely any need to expand on Todd's posts, sometimes I do it anyway. I have mostly used alternating layers of 18oz roving and mat to cover the rusty swiss cheese that used to be the steel floor of my car back in the 70s. (It is hard to drive while sitting in a rocking chair, and hitting a puddle at 60 can be distressing.) It builds up a lot of strength and stiffness quickly and hides behind the carpet. Roving is usually treated with the same finish that allows either polyester or epoxy to wet out and bond. Volan is a common one. The bundles of fibers are huge and it just takes a while for the resin to soak in. This is what Glen L has to say:
    But because of its coarse appearance, it is not used where appearance is important, since the weave cannot be concealed without an excessive amount of resin build-up. Furthermore, woven roving is more difficult to wet out than either mat or cloth, and all these elements make it not as suitable or popular for most sheathing applications.
    https://www.glen-l.com/weblettr/webl...iberglass.html

    Polyester:
    Todd is the only person that I know of who has found a way to consistently get decent adhesion to wood with polyester. As he described it here, it took a number of trials with different products to get it to work, and on other threads he has said that the materials that did work are no longer available. I have read that there are some chemicals in various woods that keep the polyester from curing properly, which makes the bond to the wood weak. For all I know, it is just the air in the wood that stops the cure. A primer is needed that bonds well to the wood, blocks the cure inhibiting substances and bonds well to polyester. It just isn't worth the trial and error for a one off.

    I have also read that a hot batch can act as a primer. (Some excess catalyst in the poly can overcome the stuff in the wood that stops the cure reaction) That primer layer may have to be an air inhibited resin because the wax that segregates out to the surface in the non-air inhibited resin will also segregate out between the resin and wood. -- Too much chemistry and too little information.

    Plywood:
    I used BCX fir plywood with one or two layers of 6 oz glass to builda boat and left it in a fresh water lake all summer for 7 years. The bottom is fine. I didn't glass the inside of the transom and it checked. Fir checks unless you glass it, so after it checked, I glassed it and it has been fine ever since. I do bail it out as soon as it rains. It is a Bolger instant boat, no gorgeous work of art, but it serves its purpose. I have a friend who used BCX on the same design. I don't know how he stored it, but after 25 years it was still sound.
    Last edited by MN Dave; 07-04-2018 at 02:39 PM.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  7. #42
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    Default Re: Polyester resin for plywood boat build

    What we ended up using was a primer of Pratt and Lambert Vitroloid lacquer sanding sealer. I don't even remember how we found that particular one. The sealer soaked into the wood pretty well, and the resin bonded well to the sealer. It smelled like a huge banana, and even the best cartridge masks had trouble keeping up with the fumes. It was rolled on in two thin coats and thankfully that step went pretty quickly. A stray spark would probably have sent the entire garage into the next block. Then we used the same polyester resin that Wilderness Boats was using in Oregon. It was Techniglass 329-2 polyester unwaxed laminating resin. It was a formula designed for production boatbuilding in the Washington/Oregon area's typical weather conditions. We were in central Illinois, but could never find a polyester that worked better and resisted delamination upon impact nearly as well.

    I remember the first time I nailed one of those rocks that hide invisibly and just under the surface in quiet water, at speed in a fully loaded strip canoe. The floor humped up enough that you could see the packs move and it made an absolutely horrible ripping noise, like it was tearing the bottom out of the canoe. We rushed to the nearest shore, unloaded the boat, turned it over - and there was a scratch. That's all, just a scratch, and a little varnish when we got home would hide most of it. Most polyester resins would have delaminated for several inches on either side of the impact area and would have required a substantial repair and some new glass in that area.

    If I could still get that resin today, I wouldn't have a problem with the idea of building strip canoes from it, but it is no longer made. For most boat stuff though, epoxy is far superior and less problematic. It's also a lot easier to use. If you think we see a lot of pilot error these days with people screwing up epoxy projects, mix ratios, etc. that's nothing like we would see with polyester.

    I still own one stripper with Techniglass polyester resin and 10 oz. fiberglass over redwood strips from about 1975 or 76 and still doing fine.

    Big Canoe.jpg

  8. #43
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    Default Re: Polyester resin for plywood boat build

    Mmmmm,....... I wouldn't tell companies like Chris Craft, Higgins, Topper, Trojan, Owens, and probably a hundred others that you canít build a plywood boat without glassing it.

  9. #44
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    Default Re: Polyester resin for plywood boat build

    These discussions always put Epoxy against Polyester, what about Vinylester?

    Twice the price of Polyester but a fifth the price of Epoxy here in the UK

    The other thing if you were laminating a GRP layup you would not just use woven rovings, you would alternate the WR with chopped strand mat (CSM). The sharp fibre of the CSM is supposed at a microscopic level knit onto the WR and provide a mechanical connection.

    The OP requirements are longevity and cost over weight - what about abrade the plywood, later of CSM and then a thin layer of WR.

  10. #45
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    Default Re: Polyester resin for plywood boat build

    Quote Originally Posted by nedL View Post
    Mmmmm,....... I wouldn't tell companies like Chris Craft, Higgins, Topper, Trojan, Owens, and probably a hundred others that you can’t build a plywood boat without glassing it.
    Good point Ned. After posting yesterday I thought that if I needed to save money I would use better quality wood and no fiberglass.

  11. #46
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    Default Re: Polyester resin for plywood boat build

    Quote Originally Posted by johngsandusky View Post
    Good point Ned. After posting yesterday I thought that if I needed to save money I would use better quality wood and no fiberglass.
    My open canoe is 4mm good ply, carbon on the INSIDE just where I sit / stand. It gets taken doen rapids and weirs and gets scraped through the first veneer. Very infrequently the scratches get painted over. If it was sheathed with glass I still think sctaches would got through to the wood. I feel such a scratch would not dry out as easily and the wood would suffer. Epoxy and sheathing only works if the integrity of the sealing works 100%. On my race dinghy I epoxied around the mast gate, chipped the area putting the mast if first day of the season - whole area was seriously rotten 8 months later.

    Use good ply and let it breathe

  12. #47
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    Default Re: Polyester resin for plywood boat build

    I've built several canoes and rowboats out of cheap plywood and only epoxy-glassed the bottom. Paint on wood for the sides. They don't fall apart instantly.

    It depends a lot on how you store them.

    But on the other hand the 10 ft punt I designed and use as a tender for the ketch is now rotting on the sides. I wish I'd used top-grade plywood. But that was 10 years ago, and money was a bit tighter for me then.

    One point -- it's a positive PLEASURE to build using the best materials. It feels good. The wood, and coverings, work easily and well. You enjoy them. Consider the building experience itself -- make it as rewarding as possible.

  13. #48
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    Default Re: Polyester resin for plywood boat build

    Vinylester seems to have the same problems for use on wood that polyester has. Your composite layers may be stronger and have a bit more flexibility before failure, but your boat as a whole probably won't be any better - just more expensive.

    I think an awful lot of the theory that a piece of painted or varnished wood is able to "breathe" is bunk. The rate of any moisture escaping through a good paint job is a heck of a lot slower than some folks think it is. Moisture getting into and under paint or varnish will often tend to lift it. I guess that would be one way to "breathe"......

    I have nothing against good quality painted plywood with no resin of any sort involved. There have been thousands of successful boats built with it. If they are going to last though, they need to be decently built, from decent materials, and then reasonably well maintained and properly stored when not in use. Most of the serious deterioration on boats seems to happen during storage, not when they are actually in use. If you plan to leave it outside, or in the water, it had better be built well and from quality materials. Yes, they cost money, but so does building a cheap one every two seasons because its substandard materials self-destructed.

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