Plywood Vs. Veneer in Cold Molding of boats with Compound Curvature

Discussion in 'Wooden Boat Building and Restoration' started by fpjeepy05, Jan 18, 2013.

  1. cavalier mk2
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    cavalier mk2 Senior Member

    I don't think you've worked out the engineering.....The Gougeons did. There are some good articles on the build. In a cold mold the glue lines are much thicker than can be achieved under the heat and pressure of plywood manufacturing, so even with 5 plies the thin viscosity resorcinal doesn't add much weight. Is hot molding superior? Perhaps....it was used on the WW2 Spitfire fighter and Mosquito bomber but takes large autoclave molds making it impractical for one off design construction.
     
  2. Oyster
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    Oyster Senior Member

    There are several stages to creating solid veneers, which also can create a huge amount of waste. Its not just running boards thru a resaw. Thats just the first stage. What you need to do is to first resaw rough cut veneers, which needs to be thicker as a rule. The run them either thru a drum sander for the softer woods or run the harder woods and thicker veneers thru a finish surface planer.


    Then even after the glue up stage, you still need to have enough thickness in which to board sand the layer, cleaning up the layup so that you can glue your next layer and also have a uniform fairness so that you will not transmit any highs and lows to the next layer. The more layers you use, the worse the lumps are when you get to the final layer.

    While the same applies to plywood veneers, by the simple nature of thin solid veneers that do not always hold their flatness after resawing, your work is extremely increased while the waste is increased in just the boarding stage.
    Kiln dried cedar, which is the order of the day in the eastern part of the states, unless you find a sawyer, the lack of moisture content when you create veneers from planks create a brittle veneer. So if you plan to build a boat under thirty foot, your task is complicated if you plan on having a shiny and slick surface using any two part paints in particular.
     
  3. fpjeepy05
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    fpjeepy05 Senior Member

    "Plywood does, however have some disadvantages. Its is expensive and does not have the potential strength of veneer." -The Gougeon Bros. on Boat Construction Pg. 75

    The Gougeons did do the engineering, and they proved that veneers were stronger.

    "You can cut laminating stock yourself, but you may run into problems... if you are making 1/8" veneers, you will lose at least 50% and perhaps as much as 70% of your stock to sawdust... We usually buy sliced veneers and have found that they are cheaper than those we saw ourselves." -Gougeon Bros.
     
  4. cavalier mk2
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    cavalier mk2 Senior Member

    Jeepers creepers! The point you are intent on missing is bang for the buck in terms of cost in materials- wood, epoxy and labor . And performance including weight and strength required. Those are some of the elements that need to be balanced for a successful design or build. Being ahead in just one can cost the race or project if it is too expensive for the results achieved. Those are the things the Gougeon's balanced to build Rogue Wave which came out lighter than the foam/glass Gulf Streamer, less costly to build and faster to boot. You need to look at the big picture not one element to understand the engineering used to produce the required results. 3 laminations would have been a deal breaker and not a faster boat.
     
  5. cavalier mk2
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    cavalier mk2 Senior Member

    Even if ply was too expensive I'd still prefer double diagonal planking if it could handle the curves. A heavier glass/other fiber skin than ply uses might be worth considering to protect the outer layer and add cross grain strength. Ply is comparatively stable dimensionally so won't swell like cedar, for instance, if the outer membrane becomes compromised.
     
  6. Oyster
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    Oyster Senior Member

    Hum, stable? The problems with neglect has little to do with the materials. Just look at some of the wooden boats on the hard that you can go up to and pick out parts of the planking with your fingernail. I take it that you have never seen plywood "Cancer", that is water that had entered behind the glass and continued to be ignored.

    I don't know who you are responding to, but in particular I am not attempting to sell cedar veneers as a way to go for this particular discussion. I have given the pitfalls of the idea of resawing your own cedar veneers, both in the work and need for a lot more wood to net out enough wood to do a certain job.

    Here in is the problem, finding a source and for the average homebuilder the costs! It ain't cheap in dollars. So one needs to weigh the the advantages versus what a person is willing to pay or can pay. Access in remote regions of the world or even in the U.S. does have its limits. I have personally done it and have added my particular thoughts. But some woods are better than others. Juniper is not my choice of woods for thin veneers, which is also required in small to mid range size boats and its readily avaliable within ten minute drive too. YMMV
     
  7. cavalier mk2
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    cavalier mk2 Senior Member

    No pearls there Oyster. I was in fact responding to fpjeepy. The dimensional stability refers to the fact that ply doesn't move as much as cedar. Nobody advocated neglect. This helps prevent collateral damage but repairs must be made ASAP. Your assumptions about what I have seen regards to any type construction are incorrect..

    The hulls are a really bad place to use less than great materials . Everything else can be upgraded but the foundation is along for the whole ride. Economies there always cost more in the long run. I'd suggest getting a business/resale number and buy everything you need wholesale. If you can combine orders with other builders economies of scale can be achieved.
     
  8. Oyster
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    Oyster Senior Member

    Hum, glassed plywood does not swell after its been properly glassed, or we would have some serious problems in a lot of expensive boats in particular, unless an avenue has been created in which moisture is allowed to enter.
    This was your response in which I responded to and concluded that in order for any and all wood to either swell or take on a new dimension, both wood and plywood needs to have moisture presented to it.
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    'Swell as much as cedar' would be better use of English. The further North you go there is also the danger of moisture in the wood freezing and expanding causing cracks in the membrane. This one tends to happen during the winter haul out. Glad we can sail year round!
     
  10. fpjeepy05
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    fpjeepy05 Senior Member

    Was Rogue wave built with ply to be a lighter, faster racer, or because of the labor savings? I'm sure the Gougeons could have made a boat that was lighter or cheaper than the rogue wave, but not both. Your first comment seemed to be refuting that veneer built boats were stronger, stiffer, and lighter than plywood boats. Do you believe this? because there are many people that would disagree with you. Can you reference the article that explains this?

    Gougeons said themselves that plywood is more expensive and not as strong as veneers. And generally speaking, the racing segment of the market is not as cost conscious as the rest of the market IMHO.

    3 Laminations of what? Plywood or veneer? 3/32", 1/8", 5/32", Mahogany, fir, cedar, paulownia, balsa, with 6oz glass skins, 10oz, 12oz, carbon/kevlar skins, large or small stringer/bulkhead spacing. There are many other variables. There are plenty of ways to make a "3 lamination" boat that would have been faster, likely all of them could have cost more.
     
  11. fpjeepy05
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    fpjeepy05 Senior Member

    I was just pointing out that the Gougeons came to the same conclusion that you did. I personally have called several veneer manufacturers to inquire about sliced cedar or paulownia veneers and most haven't even returned my calls. I think if one of the big boys like Jarret Bay were to establish a business directly with a veneer manufacture, then it might be easier for everyone else to get the same products, but maybe not. I just don't think that the home builders make up a big enough market, and i don't even know what else a slice veneer can be used for. Wood blinds, shutters? haha
     
  12. cavalier mk2
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    cavalier mk2 Senior Member


    Reference post 19 Jeepy. It is good to see you reading a manual and learning. Researching the articles for yourself will broaden your horizons.
     
  13. fpjeepy05
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    fpjeepy05 Senior Member

    I'm always learning. The day I stop will be the day they put me in the ground.

    I've searched, if it existed, you would provide it.

    “The recipe for perpetual ignorance is: Be satisfied with your opinions and content with your knowledge.” :)
     
    Last edited: Feb 20, 2013
  14. cavalier mk2
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    cavalier mk2 Senior Member

    Looks like you're carrying a shovel....

    Jeepy, if a builder jumps to conclusions they should be the right ones. It takes patience, perseverance and practice to learn the art of boat building. Dedication, desire and determination too. Not to mention the care, courage and calculations necessary for success. You've looked around for 1 afternoon and nothing is there? Methinks a Wooden Boat magazine, if such a thing existed would surely have recorded such an event. They might even have archives.....but such things you say can't exist....maybe that is a good thing. It would be tragic to see the odd sentence excerpted from such a record. After all a nail does not make a boat or a word a document, it is how they fit together that creates the whole.

    Here's to learning and using knowledge to create.
     

  15. fpjeepy05
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    fpjeepy05 Senior Member

    Cavalier, I think you might be showing your age a little on this one. Are you referring to the article in Issue #23 July/Aug 78? or Issue #202 May/June 2008. Haha, just messing with you. I'll download them and give them a read. Thanks for the hint.
    Also my engineering is a little rusty I was wondering if you could help me out with the strength to weight derivation that is generally used for planes and boats when it comes to material selection... I'll give you a hint this time. F=Pi^2*E*I/(KL)^2
     
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