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Thread: Will plywood do this?

  1. #141
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    So, with this deck:

    Attachment 10816

    Assuming that all the panels are 4 mm okume plywood, the panels will weigh in at .023 ton, or 51.52 lb., with the center of gravity a 5.5 ft. and the center of buoyancy at 6.36 ft.

    Attachment 10819
    I would use chopped fiberglass and epoxy for the fillets. Don't know what that would weigh.
    Have you includes the weight of any framing in the panel weights? You can approximate by smudging the framing over the panel by upping the thickness.
    Does chopped strand not have a reputation for not bending into the corners? Woven tape was always used for S & G.
    It really is quite difficult to build an ugly wooden boat.

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  2. #142
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    Default Re: Will plywood do this?

    I believe he wants to put corners in with a radus using chopped strand filler. BTW fiberglass putty weighs about 9.5 lbs a gallon.

  3. #143
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    Default Re: Will plywood do this?

    John,
    Are these lines the fini?

  4. #144
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    I believe he wants to put corners in with a radus using chopped strand filler. BTW fiberglass putty weighs about 9.5 lbs a gallon.
    Fairy nuff, but it will need tape between the bottom skin and topside at the forward quarter, 'cos that joint is flat transitioning to a corner as it goes aft. Could be done by taping over the filled putty fillet.
    It really is quite difficult to build an ugly wooden boat.

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  5. #145
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    Default Re: Will plywood do this?

    I am guessing that is his plan. A 1/2" or 3/4 radius makes glassing in much easier and without voids. Much less regrinding and sanding after hardening.

  6. #146
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    I am spectacularly anal-retentive about weights and centres, probably from being associated (fortunately at a distance) with a major project that went badly wrong due to a cavalier attitude toward weight control during construction. Does your weight estimate include solid wood rails, ply bulkheads, deck beams, coamings, 'glass & epoxy sheathing, rigging, deck hardware, etc., etc.?
    It includes only what I have said. I need some guidance in estimating all that furniture.

  7. #147
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    Have you includes the weight of any framing in the panel weights? You can approximate by smudging the framing over the panel by upping the thickness.
    Does chopped strand not have a reputation for not bending into the corners? Woven tape was always used for S & G.
    I used chopped fiber mixed with epoxy for the fillets in Meerkat. I shaped them with waxed paper so that they wouldn't require a lot of sanding.



    I mixed it to the consistency of peanut butter, and had no difficulty shaping it into the chines. The build thread is here: http://forum.woodenboat.com/showthre...-small-catboat

    I'm sure you're right about the flat joints needing tape.

  8. #148
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    John,
    Are these lines the fini?
    I sure hope so! I'm hoping it can be built in 4 mm, but not sure it can be done in anything thicker than 3 mm.

  9. #149
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    Default Re: Will plywood do this?

    John, at this stage of the design spiral, you don't need to be too precise in your weight estimate, but you should try to identify all parts of the boat, list them on a weights & centres spreadsheet, and estimate, calculate or get manufacturer's weights for each item. You can pick the CG for each from your design drawing. Check your email; I'll send you an Excel spreadsheet in a few minutes.

    For stuff like seats, estimate or calculate the volume of the seat planks and multiply this by the weight per cube for that species. You should be able to get mass data for different species on-line. Note that the mass given is usually at a very low moisture content, so the wood that you use will be up to 10% heavier.

    For hardware, you should be able to find weights for similar hardware on-line. Ronstan is good for this information. For little stuff such as screws, estimate the weight of all of 'em and pick a CG by eye based on your estimate of where the majority of them are located.

    Let me know what your 'glass sheathing fabric and what epoxy will be and I can give you a weight per square foot for the laminate.

    Sometimes the plethora of information can be overwhelming. It is good practice to make a spreadsheet of accumulated data for reference. It comes in handy for future projects, too.
    Hope for the best, but plan for the worst.

  10. #150
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    I sure hope so! I'm hoping it can be built in 4 mm, but not sure it can be done in anything thicker than 3 mm.
    I'll cut the parts for a 24" model, you will need to skin the bottom. PM me your address and I'll send it to you.

  11. #151
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    John, at this stage of the design spiral, you don't need to be too precise in your weight estimate, but you should try to identify all parts of the boat, list them on a weights & centres spreadsheet, and estimate, calculate or get manufacturer's weights for each item. You can pick the CG for each from your design drawing. Check your email; I'll send you an Excel spreadsheet in a few minutes.

    For stuff like seats, estimate or calculate the volume of the seat planks and multiply this by the weight per cube for that species. You should be able to get mass data for different species on-line. Note that the mass given is usually at a very low moisture content, so the wood that you use will be up to 10% heavier.

    For hardware, you should be able to find weights for similar hardware on-line. Ronstan is good for this information. For little stuff such as screws, estimate the weight of all of 'em and pick a CG by eye based on your estimate of where the majority of them are located.

    Let me know what your 'glass sheathing fabric and what epoxy will be and I can give you a weight per square foot for the laminate.

    Sometimes the plethora of information can be overwhelming. It is good practice to make a spreadsheet of accumulated data for reference. It comes in handy for future projects, too.
    I haven't sheathed my boats in the past. Instead, I've sealed the wood with epoxy, then painted them. This is only in part because I consider fiberglass heavy and weak compared to wood, the other issue is that I really, really, hate working with the stuff. There's not going to be a lot of hardware on this boat, so most of the weight will be in the framing, rig, and centerboard case. I had thought of building a sort of treasure chest around the centerboard, in which one could carry liquid refreshment and a cold collation, but on reflection I think that could create some hard spots on the rather thin bottom. Maybe there's a way to do it and still have room to move around the boat. In any case, for now I'm thinking in terms of a thwart to brace the daggerboard.

  12. #152
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    Default Re: Will plywood do this?

    Quote Originally Posted by navydog View Post
    I'll cut the parts for a 24" model, you will need to skin the bottom. PM me your address and I'll send it to you.
    Thank you!

  13. #153
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    Default Re: Will plywood do this?

    If you post the profile view it will help me.

  14. #154
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    Default Re: Will plywood do this?

    I will agree that GRP is heavy compared to plywood of equal thickness, but not about the weak part.
    Hope for the best, but plan for the worst.

  15. #155
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    I will agree that GRP is heavy compared to plywood of equal thickness, but not about the weak part.

    I think thin light weight GRP laminations of equal weight to plywood probably have more deflection and may shear with less force than ply. Somewhere around 1/4" thick GRP overtakes plywood. In terms of equal thickness it's not even a discussion.

  16. #156
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    Default Re: Will plywood do this?

    Well, sure, glass can be made strong. The lack of stiffness is the bigger problem, which means you need cored structures. I suppose I'm just prejudiced.

  17. #157
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    Default Re: Will plywood do this?

    It is all just engineering, guys, and mixing terminology doesn't clarify it much. Stiffness, shear strength, are not interchangeable terms (but you already know this, I'm sure). Suffice it to say that plywood with a sheathing of 'glass in epoxy is stronger, stiffer, and only nominally heavier than plain plywood.

    But we digress...
    Hope for the best, but plan for the worst.

  18. #158
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    Default Re: Will plywood do this?

    Did someone imply that two distinctly different properties were the same thing?

  19. #159
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    Default Re: Will plywood do this?

    So, a little more progress. I haven't got the spreadsheet going, but I'm using the method Nick suggested to estimate weights and centers, using the layers to simulate the weights. For example, I've added considerable thickness to the daggerboard to simulate the daggerboard case weight, doubled the thickness of the deck layer to simulate the weight of the needed framing. I've also added a thwart to brace the daggerboard case and to simulate the weight of the mast step, and increased the weights of the hull panels to account for the weight of the fillets and glass tape.

    Still haven't figured out how to draft the bulkheads in Delftship. Once those are added, I expect the weight will be about 145-150 lb.

    Elegant catboat with thwart 2-14-2018 5-05-27 PM 1006x695.bmp.jpg

  20. #160
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post

    Still haven't figured out how to draft the bulkheads in Delftship. Once those are added, I expect the weight will be about 145-150 lb.

    Elegant catboat with thwart 2-14-2018 5-05-27 PM 1006x695.bmp.jpg
    I exported the lines into Draftsight, and drew the bulkheads from the appropriate station data. There is a get area function in the tools menu.
    It really is quite difficult to build an ugly wooden boat.

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  21. #161
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    Default Re: Will plywood do this?

    It just occurred to me that I might turn copies of those thwarts 90 degrees and make them into bulkheads.

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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    It is all just engineering, guys, and mixing terminology doesn't clarify it much. Stiffness, shear strength, are not interchangeable terms (but you already know this, I'm sure). Suffice it to say that plywood with a sheathing of 'glass in epoxy is stronger, stiffer, and only nominally heavier than plain plywood.

    But we digress...
    And further digress...
    While you can't easily lay up epoxy and glass as perfectly as in a sheet of G-10/FR-4, you can easily look up the properties of G-10 to see what the best possible layup will give you. G-10 is up to twice as stiff, strong and dense as any wood you can find. (Yours will be less dense, less stiff and weaker because you will have a lower glass to resin ratio.)

    Put a thin layer, say 6oz cloth (0.005", 0.127mm) on a thick layer (.25" 6.35mm) of plywood and the math says you have done little more than waterproof the surface. It will do more to stiffen plywood across the grain than with the grain. Point is that a fairly thick layer is needed to build a protective skin, and the strength and stiffness improvements are slow to accumulate as you add layers. Not at all the same with (further off topic) strip plank which has a 10:1 difference in with and cross grain strength.
    Last edited by MN Dave; 02-15-2018 at 04:37 PM.
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  23. #163
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    Default Re: Will plywood do this?

    Well, I managed to get the bulkheads in, but as soon as they were in the program stopped giving me any hydrostatics.

    elegant catboat with bulkheads 2-15-2018 4-10-13 PM 1211x598.bmp.jpg

  24. #164
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    Default Re: Will plywood do this?

    John, I am not familiar with the Freeship software; are you able to 'tell' it what the CG is, and have it run the hydrostatics based on that data?
    Hope for the best, but plan for the worst.

  25. #165
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    Default Re: Will plywood do this?

    Quote Originally Posted by mmd View Post
    John, I am not familiar with the Freeship software; are you able to 'tell' it what the CG is, and have it run the hydrostatics based on that data?
    I'm using delftship, which is slightly more sophisticated, but what I've been working on today is getting the longitudinal center of buoyancy and the thwart lined up. I tilted the bow up 5 degrees and worked from there, so that I'd get a realistic trim without losing the use of most of the aft part of the cockpit. The CG, the thwart, and the helmsman are all about 6' forward of the aft end of the waterline, according to what I've got so far. It won't do hydrostatics with the bulkheads in place, can't figure out why. At first I thought the bulkheads must be pushing through the hull surface, but that's not the case.

    My idea is to set the boat up like the English dinghies from the 1940s and '50s, with the mainsheet coming from the stern, so that if I turn my back to the bow as I tack, all I have to do is scoot my butt across the boat, and the rest is simple. Mid-boom sheeting tends to get in the way of passengers, especially as the skipper must move aft to keep the right trim with a second person aboard.

    Anyway, short answer to your question, I can't get the software to do that.

  26. #166
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    Default Re: Will plywood do this?

    Quote Originally Posted by johnw View Post
    Well, I managed to get the bulkheads in, but as soon as they were in the program stopped giving me any hydrostatics.

    elegant catboat with bulkheads 2-15-2018 4-10-13 PM 1211x598.bmp.jpg
    If you have finished refining the lines save another version just for hydros without the bulkheads in place. Then you can use one for the weight/CG calculation, and apply that data to the other for trim and stability.
    It really is quite difficult to build an ugly wooden boat.

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  27. #167
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    Default Re: Will plywood do this?

    Yes, I'm sure that's the way to do it. Thanks, Nick.

  28. #168
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    Default Re: Will plywood do this?

    Quote Originally Posted by Woxbox View Post
    Or just cold mold the bow with veneers back to the point where the radius is easy for the ply to take.
    My thoughts exactly. Plywood is already a pile of veneers so it would not be inconsistent with the rest of the boats' construction.

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    Default Re: Will plywood do this?

    Quote Originally Posted by BrianM View Post
    My thoughts exactly. Plywood is already a pile of veneers so it would not be inconsistent with the rest of the boats' construction.
    Negates the huge benefit from using a developable surface. Think Bruce's Whizzbang builds. You would be building two boats and throwing one away.
    It really is quite difficult to build an ugly wooden boat.

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  30. #170
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    Default Re: Will plywood do this?

    Quote Originally Posted by Peerie Maa View Post
    Negates the huge benefit from using a developable surface. Think Bruce's Whizzbang builds. You would be building two boats and throwing one away.
    If I use 3 mm, I'll be building two boats and keeping both. And that's probably how I'll build it, assuming I get that far. I've been sweating over a new version of the lines, trying to get to a surface 4 mm might take, but I don't think I'm likely to get the curves I want with a boat that can be built by the usual stitch and glue method in one layer.

  31. #171
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    Default Re: Will plywood do this?

    John,
    Almost all of the tortured ply hulls I have built looked different than the drawings. You kind have to start with a general idea improvise as you go along. I find that plywood is quite variable and has to be negotiated with. Unless you have some sort of jig to make it go where you want, it is almost impossible to get consistent or even you intended results.
    I think the main problem is not the radius of the forefoot but some stations aft where ther is a tight turn just below the chine. I have taken quite a few pages from Phil Stevenson' moth building method. Also from Gougeon's. Both of which talk about methods for developing additional section curvature low in the hull. Phil recommends tabbing with carbon fiber because it is stiffer and will force more curvature than glass. He is right. He also bends things fore and aft to help bring panel edges together for taping and then flexes them back. It' kind of a dark art.
    There is no reason why you cannot have a few stations for the hard parts in the bow and less for the easy parts like the rest of the hull. I have cut multiple wedges out of the bow panels on some of the ICs which kind of approximate what planking would look like, and pushed them into place and glued then together. It is like strip planking, in that a ply of glass will be required to make up the strength. Otherwise there are sleazy things like stuffing a big block of foam in and shaping it to taste and adding some glass.
    Finally, it is possible to thermoform wood by gust getting it hot enough and bending it over a form. On this case, build your cone out of something like aluminum, put heaters under it and gradually get the plywood to drape over it using weights and straps.
    Trying to make"pure" stitch and glue boats without some fauxjoise ( pronounces fooog-wa) meaning "with ease we sleaze" problem solving. The whole technique is kind of a dirty trick, which while potentially elegant, isn't "proper" boatbuilding.
    SHC

  32. #172
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    Default Re: Will plywood do this?

    Quote Originally Posted by SHClark View Post
    John,
    Almost all of the tortured ply hulls I have built looked different than the drawings. You kind have to start with a general idea improvise as you go along. I find that plywood is quite variable and has to be negotiated with. Unless you have some sort of jig to make it go where you want, it is almost impossible to get consistent or even you intended results.

    SHC
    Read this and weep

    http://forum.woodenboat.com/showthre...MK-2-new-build
    It really is quite difficult to build an ugly wooden boat.

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  33. #173
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    Default Re: Will plywood do this?

    Quote Originally Posted by SHClark View Post
    John,
    Almost all of the tortured ply hulls I have built looked different than the drawings. You kind have to start with a general idea improvise as you go along. I find that plywood is quite variable and has to be negotiated with. Unless you have some sort of jig to make it go where you want, it is almost impossible to get consistent or even you intended results.
    I think the main problem is not the radius of the forefoot but some stations aft where ther is a tight turn just below the chine. I have taken quite a few pages from Phil Stevenson' moth building method. Also from Gougeon's. Both of which talk about methods for developing additional section curvature low in the hull. Phil recommends tabbing with carbon fiber because it is stiffer and will force more curvature than glass. He is right. He also bends things fore and aft to help bring panel edges together for taping and then flexes them back. It' kind of a dark art.
    There is no reason why you cannot have a few stations for the hard parts in the bow and less for the easy parts like the rest of the hull. I have cut multiple wedges out of the bow panels on some of the ICs which kind of approximate what planking would look like, and pushed them into place and glued then together. It is like strip planking, in that a ply of glass will be required to make up the strength. Otherwise there are sleazy things like stuffing a big block of foam in and shaping it to taste and adding some glass.
    Finally, it is possible to thermoform wood by gust getting it hot enough and bending it over a form. On this case, build your cone out of something like aluminum, put heaters under it and gradually get the plywood to drape over it using weights and straps.
    Trying to make"pure" stitch and glue boats without some fauxjoise ( pronounces fooog-wa) meaning "with ease we sleaze" problem solving. The whole technique is kind of a dirty trick, which while potentially elegant, isn't "proper" boatbuilding.
    SHC
    Thank you! I wonder if it would help if I made up a series of bulkheads forward? I'm certainly not above using heat and other plywood Torquemada techniques if it will produce the boat. I've been thinking the only way to do this boat is with two layers of 3 mm, do you agree?

  34. #174
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    Default Re: Will plywood do this?

    John, you can do it somehow.
    The area I think is challenging is the 5th station from the bow just below the chine is a small fairly sharp radius. I think that if you raise the chine mid ship so that it is at the lwl then the waterline wil be fairer and the transition into the rising chine line forwad will be easier and that sharp little bend will go away.
    SHC

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    Default Re: Will plywood do this?

    Quote Originally Posted by SHClark View Post
    John, you can do it somehow.
    The area I think is challenging is the 5th station from the bow just below the chine is a small fairly sharp radius. I think that if you raise the chine mid ship so that it is at the lwl then the waterline wil be fairer and the transition into the rising chine line forwad will be easier and that sharp little bend will go away.
    SHC
    That will be no tighter or even less tight than the curves forward, just part of the conic form that defines the bottom panel. The only way to change it is to change the curve of the forefoot to an easier curve.
    It really is quite difficult to build an ugly wooden boat.

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