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Thread: Will plywood do this?

  1. #71
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    If one kerf-cuts the plywood to wrap it around a tight curve, how does one restore the structural strength of the plywood? After all, you have reduced the structural thickness of the plywood by - what? - 50%? 75%? The curved panel will be stronger that a flat one, but not enough to restore all of the lost strength. Just sayin'...
    You fill the kerfs with thickened epoxy just before you bend it into place. As you bend the extra epoxy squeezes out. Then, once it is fixed in place you trowel away the squeeze out. Once the epoxy sets it's going to be stronger than the original plywood.

  2. #72
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    Default Re: Will plywood do this?

    Quote Originally Posted by cracked lid View Post
    You fill the kerfs with thickened epoxy just before you bend it into place. As you bend the extra epoxy squeezes out. Then, once it is fixed in place you trowel away the squeeze out. Once the epoxy sets it's going to be stronger than the original plywood.
    Yes, but how do you cut all those tiny kerfs?

  3. #73
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    Default Re: Will plywood do this?

    What part of "I have built this boat at 12' out of one sheet of ply on the bottom of each side do you not understand?
    I suggest that you read up on Conic Projection. Kinney's Skene's edition 8 pp107-8 & 112 discusses it, so you can play with the method.
    Excuse me. What's with the anger?
    With what he's wanting, I'm just offering a solution to his design using a different build method, but achieving the boat that he wants. In the end, its up to him and that's ok too
    Last edited by Mark Bowdidge; 01-30-2018 at 10:27 PM.

  4. #74
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Yes, but how do you cut all those tiny kerfs?
    You'll need a squadron of wee leprechauns, wielding tiny Japanese pullsaws. See Pat Ford for all current hiring details... and lay in a stock of gargle-potion <G>
    David G
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  5. #75
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    Default Re: Will plywood do this?

    Quote Originally Posted by David G View Post
    You'll need a squadron of wee leprechauns, wielding tiny Japanese pullsaws. See Pat Ford for all current hiring details... and lay in a stock of gargle-potion <G>
    Well, it's got to be better than using the dangerous, loud, and imprecise circular saw I inherited from my father...

    Jamison's?

  6. #76
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    Default Re: Will plywood do this?

    Quote Originally Posted by Mark Bowdidge View Post
    Excuse me. What's with the anger?
    With what he's wanting, I'm just offering a solution to his design using a different build method, but achieving the boat that he wants. In the end, its up to him and that's ok too
    Nick has in the past been very kind and patient with me, and generous with his knowledge. He's not just a retired naval architect, he's also an experienced wooden boat guy, and although the pictures on his wonderful thread about designing a coble in Freeship got eaten so that now you can't see them, I assure you, he knows the limits of the program. I think you got his goat by claiming that what he and Delftship see as a developed surface is in fact a compound curve. I think Nick is right in thinking it is a developed surface, at this point I'm just trying to decide whether there's a way to actually build it that's practical. You and others have been helpful, and I'm sure will continue to be so as long as we respect each other's opinions.

    Now, how complicated is vacuum bagging, really?

  7. #77
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    Default Re: Will plywood do this?

    Vacuum-bagging is not that difficult. But this thread is getting rather acrimonious, and my previous descriptions of successful bagging methods for one-off projects was met with significant opposition which I don't think will be productive if repeated, so I'm out. If the OP would like to contact me off-line, I will be glad to offer what I know. I just don't think it is productive for anyone involved to argue publicly.
    Hope for the best, but plan for the worst.

  8. #78
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    Vacuum-bagging is not that difficult. But this thread is getting rather acrimonious, and my previous descriptions of successful bagging methods for one-off projects was met with significant opposition which I don't think will be productive if repeated, so I'm out. If the OP would like to contact me off-line, I will be glad to offer what I know. I just don't think it is productive for anyone involved to argue publicly.
    I was hoping we could return to civility with a non-controversial subject like vacuum bagging, but I guess I misjudged the level of controversy possible on that delicate subject. It's like I brought up religion, or CPES.

    Guys, it's just a nice little shape I'm thinking it would be nice to build. The dream can change and adapt to reality.

  9. #79
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    Default Re: Will plywood do this?

    johnw, sorry that I am irritable this evening. I'll check in again tomorrow. Maybe I'll be in a better mood then.
    Hope for the best, but plan for the worst.

  10. #80
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    Default Re: Will plywood do this?

    Too much hassle. Just make it hard chined for the full length. Will it be a little bit slower? Maybe, maybe not, but you can probably recover the speed by stretching it a foot or two.

  11. #81
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    Default Re: Will plywood do this?

    I may have missed it but - have you tried a scale model in card or th 1mm ply that model aircraft folks use?
    Creationists aren't mad - they're possessed of demons.

  12. #82
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Yes, but how do you cut all those tiny kerfs?
    Originally Posted by Me; The way I have done it is with a circular saw and a guide. The saw blade can't cut any deeper than it has been set. A router with a V-groove bit could be used too.
    Quote Originally Posted by cracked lid View Post
    You fill the kerfs with thickened epoxy just before you bend it into place. As you bend the extra epoxy squeezes out. Then, once it is fixed in place you trowel away the squeeze out. Once the epoxy sets it's going to be stronger than the original plywood.
    You need to work quickly unless you use slow hardener on a cold day.
    Quote Originally Posted by johnw View Post
    Well, it's got to be better than using the dangerous, loud, and imprecise circular saw I inherited from my father...

    Jamison's?
    A lot of the noise comes from the blade. You might be surprised at how much quieter a Freud Diablo blade is on the same saw.

    Jamison's is good, but for boats a good Aņejo rum goes well.

    There is no law against mixing strip with ply. The traditionalists will hate you either way. I have to agree with Navydog though Post #53
    Last edited by MN Dave; 01-31-2018 at 02:09 AM. Reason: linking the poster is bad enough folks is too upset to look at the picture
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  13. #83

    Default Re: Will plywood do this?

    Your post reminded me of a text file I found a long time ago when researching one sheet boats. There was one called the Loonie, who's designer also had this bending table on his site. Unfortunately the site is gone now, but luckily I saved a few pages.

    Code:
    Bending Plywood
    
    
    The following rough guide for the maximum bend in a sheet of dry 
    plywood comes from "Boatbuilding Manual 3rd edition" by Robt. M. 
    Steward (1987). The bend is given as the smallest radius of 
    curvature to which the plywood should bend without deforming. I 
    developed a formula to answer the question, "I want to bend a 
    sheet of plywood 3 inches in 6 feet, what's my radius of 
    curvature?". The formula I came up with is explained following the 
    guide.
    
    
    Bending guide - all measurements in inches.
    
    
    plywood         min across        min with
    thickness       grain radius      grain radius
    
    
    1/4                24               60
    5/16               24               72
    3/8                36               96
    1/2                72              144
    5/8                96              192
    3/4               144              240
    
    
    The table tells us 1/4 inch plywood sould bend into a 4 ft circle 
    across the face grain and a 10 ft circle with the face grain.
    
    
    
    
    The formula for radius of curvature in inches (r") is:
    
    
             b"    l"**2 
       r" = --- +  -----
             2       8b"
    
    
       where b" is the inches depth of the bend and
             l" is the inches straight line length of the bend
                (not the curved length of the bend)
                and "**2" means "squared"

  14. #84
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    Default Re: Will plywood do this?

    Quote Originally Posted by Mark Bowdidge View Post
    Excuse me. What's with the anger?
    With what he's wanting, I'm just offering a solution to his design using a different build method, but achieving the boat that he wants. In the end, its up to him and that's ok too
    I was getting ticked off with several posters, not only you saying that it can't be built because of double curvature after I had posted that I know it is only single curvature and that I had built one. Do you enjoy being ignored to your face?
    It really is quite difficult to build an ugly wooden boat.

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  15. #85
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    So, two layers of 3 mm? It doesn't sound like 4 mm will make the curves.

    Would 3 mm with a lot of stringers work?
    I would still go with two layers. Stringers are a messy solution (draining water and cleaning the boat) and the plank between the stringers would still be fragile.
    It really is quite difficult to build an ugly wooden boat.

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  16. #86
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    Default Re: Will plywood do this?

    You still going on Nick? Crikey you make me laugh. Throughout this whole conversation, was I ever talking to you?
    Whatever... LOL
    Last edited by Mark Bowdidge; 01-31-2018 at 06:33 AM.

  17. #87
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    Default Re: Will plywood do this?

    ^ Well there you go.
    It really is quite difficult to build an ugly wooden boat.

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  18. #88
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    Default Re: Will plywood do this?

    Thanks for sticking with me, Nick. If this works, it could open whole new vistas for me in terms of what shapes I can build using stitch and glue.

  19. #89
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    Default Re: Will plywood do this?

    Not sure if this is relevant or not, but here goes. There is a builder/designer on the WBF who goes by FloMo. He designs boats with very complex shapes to be built with very little plywood Like 16 foot canoes with rounded bilges made from two sheets of plywood, in the stitch and glue style. While his work is a wonderful exercise in minimalism, and he is a heck of a nice guy, he also shows you what is possible with plywood. And I could be wrong, but I think he builds with 4mm birch, as opposed to marine plywood (again, I could be totally wrong, as I am going by memory there, as opposed to rereading his threads.)

    At any rate, his work might be worth checking out just to see what is doable, if there is some doubt about a specific design.

    CG

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    Default Re: Will plywood do this?

    Quote Originally Posted by cglynn View Post
    Not sure if this is relevant or not, but here goes. There is a builder/designer on the WBF who goes by FloMo. He designs boats with very complex shapes to be built with very little plywood Like 16 foot canoes with rounded bilges made from two sheets of plywood, in the stitch and glue style. While his work is a wonderful exercise in minimalism, and he is a heck of a nice guy, he also shows you what is possible with plywood. And I could be wrong, but I think he builds with 4mm birch, as opposed to marine plywood (again, I could be totally wrong, as I am going by memory there, as opposed to rereading his threads.)

    At any rate, his work might be worth checking out just to see what is doable, if there is some doubt about a specific design.

    CG
    I'm pretty much in awe of FloMo's work, so I'd love it if he'd weigh in. I'm not sure how to apply the lessons from his threads to this project.

  21. #91
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Thanks for sticking with me, Nick. If this works, it could open whole new vistas for me in terms of what shapes I can build using stitch and glue.
    Ono thing that might make a difference. I built on a stem/forefoot /keel. That way there was a bearding to drape around and the rebate seam was back an inch or two into the surface.
    It allowed me to bring the forefoot further out and less cutaway, and will be easier to glue together than that fine acute corner between your two shells.
    A bit like this quick sketch
    Silkie.jpg
    It really is quite difficult to build an ugly wooden boat.

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  22. #92
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    Ono thing that might make a difference. I built on a stem/forefoot /keel. That way there was a bearding to drape around and the rebate seam was back an inch or two into the surface.
    It allowed me to bring the forefoot further out and less cutaway, and will be easier to glue together than that fine acute corner between your two shells.
    A bit like this quick sketch
    Silkie.jpg
    So, there's sort of a cutwater on that model?

  23. #93
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Yes, but how do you cut all those tiny kerfs?
    If you are compelled to kerf the ply,the best option would probably be a router with a small-say 1/16" cutter running along guide battens that aim at the frustrum of the cone.In this situation you have severed a lot of the fibres of the material and just splodging filler in there isn't really the same thing as having fibre continuity.If you add a light glass cloth set in epoxy,you will probably have increased the strength for quite a small weight penalty.I have bagged all manner of core materials into laminates,but haven't actually bagged ply onto an existing wooden hull.I can imagine ways in which it might be done.

  24. #94
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    So, there's sort of a cutwater on that model?
    Yes, I built her before epoxy, so used Cascophen resourcinol and built her on a stem/keel backbone. That allowed me to shape the forefoot any way I wanted outside of the ply skin.
    If you do kerf, you should try to follow the radiating generator lines.
    It really is quite difficult to build an ugly wooden boat.

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  25. #95
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    Yes, I built her before epoxy, so used Cascophen resourcinol and built her on a stem/keel backbone. That allowed me to shape the forefoot any way I wanted outside of the ply skin.
    If you do kerf, you should try to follow the radiating generator lines.
    I'm thinking two layers of thin ply would be better.

  26. #96
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    Default Re: Will plywood do this?

    Quote Originally Posted by John Meachen View Post
    If you are compelled to kerf the ply,the best option would probably be a router with a small-say 1/16" cutter running along guide battens that aim at the frustrum of the cone.In this situation you have severed a lot of the fibres of the material and just splodging filler in there isn't really the same thing as having fibre continuity.If you add a light glass cloth set in epoxy,you will probably have increased the strength for quite a small weight penalty.I have bagged all manner of core materials into laminates,but haven't actually bagged ply onto an existing wooden hull.I can imagine ways in which it might be done.
    Thanks, I'm thinking kerfing isn't really the way I want to go. It might be interesting for some future project.

  27. #97
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    Default Re: Will plywood do this?

    FWIW Flo-mo can't find marine grade plywood in Vienna. He tried some poor quality 4mm okoume and it didn't bend well. He has had success with 4mm poplar that is still not very good. When he back lights it you can see that the inner ply is full of knots. The poplar that he is using might be one of the true poplars such as European Aspen, not the American yellow poplar. http://www.wood-database.com/wood-ar...en-whats-what/

    There are a number of threads about steaming plywood/ https://www.google.com/search?q=site...nt=firefox-b-1
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  28. #98
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    Default Re: Will plywood do this?

    Quote Originally Posted by MN Dave View Post
    FWIW Flo-mo can't find marine grade plywood in Vienna. He tried some poor quality 4mm okoume and it didn't bend well. He has had success with 4mm poplar that is still not very good. When he back lights it you can see that the inner ply is full of knots. The poplar that he is using might be one of the true poplars such as European Aspen, not the American yellow poplar. http://www.wood-database.com/wood-ar...en-whats-what/

    There are a number of threads about steaming plywood/ https://www.google.com/search?q=site...nt=firefox-b-1
    Thanks, I'll be chewing on those for a while.

  29. #99
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Station 1 has hardly any curve. Station 11, near the bow, has I think about a 2' radius.
    The forward cockpit deckbeam on a CLC Chesapeake 16 (which I have built two of) has a radius of 16" (I just checked the actual plans). 4mm 3 ply goes around that without any problem whatsoever, provided the core ply doesn't have voids. 6mm or 1/4" would struggle I think, in part because it usually has five plys, so is inherently stiffer.
    Developable conic sections are really hard to visualise from a lines drawing, and even in the flesh they look like some compound curve magic is going on!

    Pete
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  30. #100
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    Default Re: Will plywood do this?

    Quote Originally Posted by epoxyboy View Post
    The forward cockpit deckbeam on a CLC Chesapeake 16 (which I have built two of) has a radius of 16" (I just checked the actual plans). 4mm 3 ply goes around that without any problem whatsoever, provided the core ply doesn't have voids. 6mm or 1/4" would struggle I think, in part because it usually has five plys, so is inherently stiffer.
    Developable conic sections are really hard to visualise from a lines drawing, and even in the flesh they look like some compound curve magic is going on!

    Pete
    Thank you. I'm trying to figure out how to export the model so that it can be checked in some different software, which mmd has generously offered to do pro bono. The people on this forum are great!

  31. #101
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    Default Re: Will plywood do this?

    Your program (FreeShip, isn't it?) should have a 'save as' option that gives you a number of options for format to save in, or an 'export' function that will request what type of format to save the file in. That's the file I need.
    Hope for the best, but plan for the worst.

  32. #102
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    Default Re: Will plywood do this?

    It's Delftship, which has different options. I suppose I could redo the boat in Freeship, though it's a bit of work.

  33. #103
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    Default Re: Will plywood do this?

    Creationists aren't mad - they're possessed of demons.

  34. #104
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    Default Re: Will plywood do this?

    Doesn't matter the source program, John; just whether you can export the file to a format that I can use.
    Hope for the best, but plan for the worst.

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    Default Re: Will plywood do this?

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    Wish that stuff came with waterproof glues. Some friends built boats in "ironply", said to be waterproof and flexible, but it's 5 mm thick, so I doubt it would flex enough for this use.

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