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Thread: Will plywood do this?

  1. #36
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    Default Re: Will plywood do this?

    Quote Originally Posted by Mark Bowdidge View Post
    Im not talking about the stern. I'm talking about the bow sections.
    So am I.
    It really is quite difficult to build an ugly wooden boat.

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  2. #37
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    I had considered that for the stern, but I think the bow would be a bugger. How do you cut all those kerfs so precisely? Table saw?
    I wouldn't do it unless there wasn't any choice. 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.

    It sounds like you don't have a problem since the sections are conic and the radius is larger than it looks in the screen shot. If you are between a rock and a hard place, it isn't difficult to strip plank the difficult sections.

    Bending plywood is interior grade and tends to be made from non-durable woods. https://www.columbiaforestproducts.c...nglish-453.pdf "Panels are not designed for structural or exterior use."
    Last edited by MN Dave; 02-16-2018 at 02:36 PM.
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  3. #38
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    Default Re: Will plywood do this?

    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'...
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  4. #39
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    Default Re: Will plywood do this?

    4mm will wrap around the stern with no problem. The real issue is the chine in the bow.

  5. #40
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    4mm will wrap around the stern with no problem. The real issue is the chine in the bow.
    There is no chine in the bow, there is a seam between the topside plank and the bottom plank, but that is so near flat as to not be there.
    It really is quite difficult to build an ugly wooden boat.

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  6. #41
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    Default Re: Will plywood do this?

    Methinks that the terms "chine" and "turn of bilge" are being confused here...
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  7. #42
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    Methinks that the terms "chine" and "turn of bilge" are being confused here...
    Yes, a couple of posters really are muddying the waters with their confusion.
    It really is quite difficult to build an ugly wooden boat.

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  8. #43
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    Default Re: Will plywood do this?

    This boat has a hard chine. If you want to call the radius in the bow "turn of the bilge" it's really only a matter of semantics.

  9. #44
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    This boat has a hard chine. If you want to call the radius in the bow "turn of the bilge" it's really only a matter of semantics.
    When the entire thread is about bending the bottom plank around the shape at the forefoot, well away from the chine, it is a bit more important than just a matter of semantics.
    It really is quite difficult to build an ugly wooden boat.

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  10. #45
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    Default Re: Will plywood do this?

    With respect, no, not really, navydog. The terminology is precise and specific. The chine is where the upper and lower panels meet; the turn of the bilge is the sharp curve in the sections at the approximate waterline. I believe that I can speak for Nick in that it is the ability of a plywood panel to be able to be formed into the shape described in the lines plan sections at the turn of the bilge that we are questioning.
    Hope for the best, but plan for the worst.

  11. #46
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    I think that the turn of the bilge in the forward sections is too severe. Yes, you can torture plywood into fantastic shapes with the right technology, but forming jigs are expensive to build and you will have to go through expensive trials to get it right. The laminated chair that Canoeyawl posted is formed from dry laminates in a hot-glue press at about ten tons of pressure (I did work in a factory that made such things). Sorry, Canoeyawl; no insult intended. I think that the hull form you are contemplating can be approximated reasonably well in plywood, but not that form, and possibly not with a single chine.
    Just so. I see no problem with the fantail stern. I doubt you'll get even 4mm to bend into the curve shown forward at the turn of the bilge. Not consistently, and fairly. At least not without extraordinary measures.
    David G
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  12. #47
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    Default Re: Will plywood do this?

    Precisely, and the bottom panel plywood edge will run along the chine and continue to the stem on the same linear path. The top edge of the plywood will require a chine log to hold the edge in or it will oil can.

    The primary feature of this boat is a vee bottom and hard chine. Transitioning to a soft chine doesn't mean it there isn't one.

  13. #48
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    Default Re: Will plywood do this?

    Quote Originally Posted by David G View Post
    Just so. I see no problem with the fantail stern. I doubt you'll get even 4mm to bend into the curve shown forward at the turn of the bilge. Not consistently, and fairly. At least not without extraordinary measures.
    Yep, my experience with an almost identical boat at 12' was that the ply I used bent round the forefoot, but was too floppy for the flat panels aft.
    I would build out of two layers of ply vacuum bagged together.
    What did Bruce use for his Wizzbang boats?
    Searching the threads turns up this:
    This is 6mm ply

    scarfed to 3/8" on the flat bit aft.. http://forum.woodenboat.com/showthre...ild&highlight=
    It really is quite difficult to build an ugly wooden boat.

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  14. #49
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    Default Re: Will plywood do this?

    Maybe we are mis-undertaking each other, navydog. My issue is not with the chine, per se, but with the shape the bottom panel is supposed to take between the chine and the keel, especially in the forward sections. It just won't take that shape regardless of how you try to form it, IMHO.
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  15. #50
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    Default Re: Will plywood do this?

    I'm in agreement with you. By far the easiest thing to do is continue the hard chine to the stem and have a vee bottom. I can't see that it would change the characteristics of the boat.

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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    Yep, my experience with an almost identical boat at 12' was that the ply I used bent round the forefoot, but was too floppy for the flat panels aft.
    I would build out of two layers of ply vacuum bagged together.
    What did Bruce use for his Wizzbang boats?
    Searching the threads turns up this:
    This is 6mm ply

    scarfed to 3/8" on the flat bit aft.. http://forum.woodenboat.com/showthre...ild&highlight=
    Irrelevant.

    What wiz uses is a proprietary admixture of magic, genius, and stubborn belief in his own idiosyncrasy. Doesn't apply to us mere mortals <G>
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  17. #52
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    Default Re: Will plywood do this?

    Navydog, if the chine stays in its present location and allowed to form a standard vee-hull bow, there will be a considerable loss of buoyancy at the bow, which will change the trim and hydrodynamic performance of the hull.
    Hope for the best, but plan for the worst.

  18. #53
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    Default Re: Will plywood do this?

    Yes there will be a small loss of buoyancy, but may improve the hydrodynamic performance through the water.
    Attached Images Attached Images

  19. #54
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    Navydog, if the chine stays in its present location and allowed to form a standard vee-hull bow, there will be a considerable loss of buoyancy at the bow, which will change the trim and hydrodynamic performance of the hull.
    Further more you could not build it out of one sheet of ply. It would impart twist to the panel which would no longer be developable.
    The only way to soften the tight curve would be to cut away the forefoot in profile.
    It really is quite difficult to build an ugly wooden boat.

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  20. #55
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    What John said. The boat I mentioned was also a conic projection with the bottom panel seam running high up the stem like that. It has been done.
    Please tell me more about how its been done. What kind of ply? I really like this shape, but I'm not sure it's to be.

    Yeadon stopped by my shop before I started this thread and suggested building this boat skin on frame, which I've not tried yet. I'm now wondering if I can build in very thin ply, then add enough stringers that I'm half way to strip planking. When I was a kid on Okinawa, I saw a man building a similar shape in thin layers of ply, pretty much cold molded, but I spoke too little Japanese to converse with him. He wasn't vacuum bagging.

  21. #56
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Please tell me more about how its been done. What kind of ply? I really like this shape, but I'm not sure it's to be.

    Yeadon stopped by my shop before I started this thread and suggested building this boat skin on frame, which I've not tried yet. I'm now wondering if I can build in very thin ply, then add enough stringers that I'm half way to strip planking. When I was a kid on Okinawa, I saw a man building a similar shape in thin layers of ply, pretty much cold molded, but I spoke too little Japanese to converse with him. He wasn't vacuum bagging.
    She was 12' long with three strakes of glued lap clinker topsides where you have one topside panel. That allowed a softer bilge with the chine developing in the aft 1/3 to 1/4 of the length. The bottom was designed with conic projection as close to identical to your bottom as a 30+ year gap will allow.
    I used 3mm ply which was OK forward, but inadequate in the run.
    That is why I am thinking two layers. With both layers full width rather than planked piecemeal you would probably need to vacuum bag to provide enough clamping pressure for the glue.
    I built and wore the boat out before the days of digital cameras, and cannot now find the only photographs that I took of her.

    I would rough out the stem-forefoot and try wrapping some ply round it to see what will go.
    It really is quite difficult to build an ugly wooden boat.

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  22. #57
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    Default Re: Will plywood do this?

    Late to the thread, but down here some designers and builders spent decades trying to put as much round as they could in the bottom sections of ply racing dinghies. I have never found out any formulae, but the amount of curvature in the design in the first post looks considerably more than guys like John Maconaghy could do with ply.

    According to Juan Baader, Cherubs like the one in the sketch below were built with cuts near the stem, angled up and aft at 45 degrees, to allow the ply to bend around the shape. He says it was then reinforced with an inner skin. The point is that these sections were pushing the limits of even light ply in a 12 footer weighing (IIRC) 50kg. CREDIT - UK CHERUB CLASS SITE

    ldwg-spen7.gif

  23. #58
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    Yes there will be a small loss of buoyancy, but may improve the hydrodynamic performance through the water.
    Not really, with respect. Many racing designers find that a U shape is significantly better overall; for example, racing dinghies have been moving away from Vee sections to U sections for decades. The U develops hydrodynamic lift to help planing; it has less wetted surface; the volume moves the bow wave forward which increases hull speed; and it provides more buoyancy. These are almost always more important than "cutting through the water" more effectively.
    Last edited by Chris249; 01-30-2018 at 04:01 PM.

  24. #59
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    Default Re: Will plywood do this?

    Quote Originally Posted by Chris249 View Post
    Not really, with respect. Many racing designers find that a U shape is significantly better overall; for example, racing dinghies have been moving away from Vee sections to U sections for decades. The U develops hydrodynamic lift to help planing; it has less wetted surface; the volume moves the bow wave forward which increases hull speed; and it provides more buoyancy. These are almost always more important than "cutting through the water" more effectively.
    That's all fine but, it's not going to help john build this in plywood.

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    Default Re: Will plywood do this?

    The spot the red arrow points to is about the tightest bend I'd attempt with 4mm okoume; there might be some compounding present there as well. I was really surprised it didn't crunch. In the linesplan it looks much tamer than your front end.

    Kid boat chine.jpgKid boat chine1.jpgKid boat chine3.jpgKid boat chine4.jpgkid boat Linesplan.jpg

    I don't trust the design software anymore to tell me whether it's developable but I trust a model. Thick Bristol board balked at super tight bends or compounding at 1:10 scale but took gentle curves no problem. Thin Bristol board was too flimsy.

    I have managed to get some horrible abominations of panels out of Freeship and didn't even bother modeling those. The software screwed up with the panels for the boat above and I skipped the paper model, bad mistake. I will never attempt building a boat again without a model.

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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    That's all fine but, it's not going to help john build this in plywood.
    Maybe, but it addresses your point, and it shows why designers often tried to put as much curve in the forward sections as they could and therefore that looking at the radius of later ply racing designs could provide useful information on the maximum possible sectional curve, which is directly on point.

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    Default Re: Will plywood do this?

    That's nice Claudia. It looks more than stable enough for a nephew with such a low center of gravity (the boy I mean). Have they tried it in the water yet?

    I remember you were having some sort of issue with painting. Did the kid's dad put on the finish coats or were you able?
    Last edited by Gib Etheridge; 01-30-2018 at 04:57 PM.

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    Default Re: Will plywood do this?

    That's why we don't use Freeship with any of our designs. Its "free" for a reason.
    We only use Maxsurf for hull development and Rhino for other parts.

    In regards to your "model", your chine from the transom to midship is right on the turn of the bilge, but forward of this, it sweeps up to nearly the top of the stem. Here's your problem. The bottom plate in the aft sections is flat and only has single curvature (bending in 1 plane only), but from here forward, your trying to not only bend it towards the stem, but also bend it around the turn of the bilge to become a part of the topsides plate. This is double curvature. Plywood/ alloy or steel won't allow you to do this. You end up with all sorts of issues. That's why they're built using smaller plates. Its the same for power boats with "flare" in the topsides plate. You can't bend the ply/ alloy or steel around from transom to the bow in one piece. That's why they are either strip planked or cold molded. It due to double curvature, but in the reverse direction.

    Now if I were designing such a boat using your plan above, I would design it using 3 parts. The topside plate and the bottom plate would be ply and the forward section at the turn of the bilge would be planked. The bottom plate edge would end right a the beginning of the bottom of the radius or turn of the bilge in the forward section. The same for the topsides plate, but at the top of the radius in teh forward sctions. As you build it, the topsides plate and bottom plate would be joined together in the aft section as per normal, but from midship forward, they would slowly separate from each other and a gap would appear from here forward. This gap would then be planked.
    In the end, it would look exactly as your drawn your boat, but built differently and far easier with no stress in the plywood
    Last edited by Mark Bowdidge; 01-30-2018 at 05:30 PM.

  29. #64
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    Default Re: Will plywood do this?

    I'm beginning to think I might get something that slightly resembles this shape if I find another way to get the volume down low, such as a wide, flat keel plank.

  30. #65
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    Default Re: Will plywood do this?

    I thought Mark presented a reasonable solution to build it the way it's designed currently. Cut the molds to allow for the plank thickness. Install the planks first with rabbited edges to acept the bottom plywood and side planks.

  31. #66
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    Default Re: Will plywood do this?

    Quote Originally Posted by Mark Bowdidge View Post
    That's why we don't use Freeship with any of our designs. Its "free" for a reason.
    We only use Maxsurf for hull development and Rhino for other parts.

    In regards to your "model", your chine from the transom to midship is right on the turn of the bilge, but forward of this, it sweeps up to nearly the top of the stem. Here's your problem. The bottom plate in the aft sections is flat and only has single curvature (bending in 1 plane only), but from here forward, your trying to not only bend it towards the stem, but also bend it around the turn of the bilge to become a part of the topsides plate. This is double curvature. Plywood/ alloy or steel won't allow you to do this. You end up with all sorts of issues. That's why they're built using smaller plates. Its the same for power boats with "flare" in the topsides plate. You can't bend the ply/ alloy or steel around from transom to the bow in one piece. That's why they are either strip planked or cold molded. It due to double curvature, but in the reverse direction.

    Now if I were designing such a boat using your plan above, I would design it using 3 parts. The topside plate and the bottom plate would be ply and the forward section at the turn of the bilge would be planked. The bottom plate edge would end right a the beginning of the bottom of the radius or turn of the bilge in the forward section. The same for the topsides plate, but at the top of the radius in teh forward sctions. As you build it, the topsides plate and bottom plate would be joined together in the aft section as per normal, but from midship forward, they would slowly separate from each other and a gap would appear from here forward. This gap would then be planked.
    In the end, it would look exactly as your drawn your boat, but built differently and far easier with no stress in the plywood
    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.
    Last edited by Peerie Maa; 01-30-2018 at 07:10 PM.
    It really is quite difficult to build an ugly wooden boat.

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  32. #67
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    I thought Mark presented a reasonable solution to build it the way it's designed currently. Cut the molds to allow for the plank thickness. Install the planks first with rabbited edges to acept the bottom plywood and side planks.
    Normally, I wouldn't build a stitch and glue boat over molds, so that turns it into an entirely different project where I might as well not use plywood at all.

  33. #68
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    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?
    Nick, would 3mm bend to this shape? Or are we talking even thinner?

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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Nick, would 3mm bend to this shape? Or are we talking even thinner?
    I an sure that 3mm will, but it will be too thin for the flatter bits.
    It really is quite difficult to build an ugly wooden boat.

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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    I an sure that 3mm will, but it will be too thin for the flatter bits.
    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?

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