Plywood designs as foam core and fiberglass

Discussion in 'Boat Design' started by LazyFox, Jul 14, 2021.

  1. rberrey
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    rberrey Senior Member

    Fallguy , It is not that oversimplified , the tools to convert a ply boat build to foam are there if you look , inserts are covered in section 7 of Ed Horstman's book " Foam Fiberglass Construction " . Ed,s book is a good read and great source of boat building info . There was at least one Tiki 26 built from foam core by a company in Fl , wouldn't hurt to give them a call if building a Tiki .
     
  2. Scuff
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    Scuff Senior Member

    Lazy,
    Are you committed to the wharram design? There are other designs that support foam/glass.
     
  3. rberrey
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    rberrey Senior Member

    Warram has at least one design 29' Taneuis that has foam option in the plans . You might try calling Warram and talk a few minuets with him , or email him and ask about a tiki 30 foam option . If you look at the 29' then I would look at other 28' ( 8.5 ) cats as there are a number of older designs . It is probably cheaper to buy a cat that can be taken apart and transported .
     
  4. fallguy
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    fallguy Senior Member

    I can tell you that mislocating higher density infill is really easy to do, more so if the designer hasn't specified.

    And I said, 'you' are oversimplifying, not that it is simple. It isn't simple to convert from a ply boat to a foam one.

    Jacques Mertens has been working on converting many of his designs to foam and it takes him, as a designer, a rather long time. He is retired and has quite a few designs, but you are glossing over a lot.

    Even supporting the hull is different.
     
  5. rberrey
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    rberrey Senior Member

    Fallguy , I have a set of plans that have been converted from wood to foam so I can compare the two and converting can be done by someone that wants to convert . There is no mislocating higher density infill , it goes in the same location in a foam build as an incest or hard spot in the wood build . I have only worked on two boat builds , C-flex , which gave the bug , but I have spent most of my life doing concrete form work . A concrete form is designed based on hydraulic pressure , all boat hull,s adhere to a basic hydraulic design to keep the water out . A boat hull is no more than a concrete form in reverse , and I have been responsible for building a few million square feet of concrete form,s of all shapes and sizes . Converting material use from one type to another requires only thing , both have to do the same thing , 9mm ply with skin = 1'2 foam with skin , both do the same thing in re-guard to hydraulic pressure . As a designer Ed Horstman not only has years of designing boats ( large and small ) as a NA , but he is also an engineering degree , he can design you an airplane as well . If his book gives you the math it is good , any advice is good advice . Next point , a concrete snap tie rated at 3500 lbs , it will not hold 3500 lbs , it will hold 7000 lbs , it was designed with a 2 to 1 safety factor , many items have a 4 to 1 safety factor . When an Engineer or NA designs something they design in a safety factor out of the goodness of their hearts , or fear of liability , it will be at least 2 to 1 . You can be sure that a NA designing a sailboat for the backyard builder has factored in a large safety factor and a shorter mast than the design can handle . If LazyFox screws up by an inch or two the designer has his back . To a large degree this forum is here to help LazyFox convert to foam if that's what he wants to do , not scare him off . Gulf Coast termite problems in wood boats might another pro for foam .
     
  6. fallguy
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    fallguy Senior Member

    There is no rational person on the forum that would encourage a DIYer to arbitrarily modify a ply design to foam.

    It is unwise, and the person won't understand the cost and complications, changes to time budgets.
     
    Last edited: Jul 17, 2021
  7. rberrey
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    rberrey Senior Member

    Fallguy , I don't know about Scuff,s plans but mine are for a plywood skin on frame boat , there is one foam specific sheet for foam bulkheads , there are scant-ling.s and there is Eds book on Foam construction , maybe Scuff will chime in on his set of plans , If you take the scant-lings for ply on frame and use the math Scuff posted from Ed,s book , using a traditional layup of mat ,woven , mat ,gelcoat or finish cloth , I come up with about the same scant-lings he spec . The Tiki is a skin on frame , not stitch and glue which may have more change because of furniture being structural in most case . There is no reason he can't convert his skin on frame plans to foam .
     
  8. LazyFox
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    LazyFox Junior Member

    Guys, my main concern was learning how to calculate the material conversions, and what materials/references I should be looking at. I'm familiar with both glassed plywood, and foam core construction methods from previous projects, but on a smaller scale so I don't know how to convert. Structural integrity wasn't as much of a concern as impact integrity. Building camper trailers and surfboards I was more worried about impact strength and in turn over engineered, but with a project on this scale financial budget and material availability become the limiting factors. I'm looking for information sources because I don't know where to look for them. I asked here because search engines are biased, and I can learn more by asking people with experience than I can using search engines if I don't know what I'm look for. Until I posted here I hadn't heard heard of Ed Horstman's book, and references like that are what I'm looking for. Also, only an idiot arbitrarily modifies designs without having them verified by an engineer, but doing so can get expensive if you need the engineer to do the redesign. Learning to properly do the work myself is not only a way to save money, but gives me peace of mind knowing I understand not only the how but the why. If something needs to be repaired down the road a patch isn't going to cut it for me except in an emergency. I'm trying to be as prepared as I can be before I start dumping money into a project to avoid failure. Mistakes can get expensive in a hurry.
     
  9. fallguy
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    fallguy Senior Member

    The best money I spent on my project was paying the designer for the plans.
     
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  10. gonzo
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    gonzo Senior Member

    You are way off on understanding what a boat hull is and the stresses involved.

    That is completely incorrect. As an engineer I use safety factors depending on the use, regulations, codes and other factors. It has nothing to do with my heart or fear. Also, where did you get the 2 to 1 factor from? Seems like you are making up numbers to appear knowledgeable.
     
  11. Scuff
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    Scuff Senior Member

    I requested the foam construction sheets and he supplied them .. the design was originally diagonal strip planking over frames using plywood as the hull planking material.
    I am totally with Fallguy on the support of the designer. In my opinion second to the design is the support of the person who dreamt it up. You should interview the designer in person or over the phone if possible and if you aren't comfortable with them walk away and find another design.
     
  12. rberrey
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    rberrey Senior Member

    gonzo , out of the goodness of your heart was an attempt at humor , the part about liability is a fact and it plays a part in what an Engineer or NA designs and advice they give . No matter if the safety factor is 2 to 1 , or 4 to 1 , I suspect you put a safety factor into your designs based on what the needs are . I understand there is more involved in boat design than basic hydraulic pressure , but from a 10x20 sugart barge to a 100 yacht it is a basic part of design . A Tiki 30 is not a high speed planning hull where the skin might fly , it is a skin on frame design where the hull material could be changed from wood to foam without problem if he did a little reading .
     
  13. gonzo
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    gonzo Senior Member

    I assume you are referring to static pressure. In that case there is a gradient from a maximum at the bottom of the keel to zero at the waterline. It is a factor in design, but it is not the only one or most important.

    I think that "a little reading" is what makes you believe that. Changing a design from wood to composite requires re-engineering the design. For example, how do you compare puncture resistance, toughness and stiffness? Your cavalier attitude about dismissing proper engineering is bad advice. Ultimately somebody needs to be responsible for a complete deviation in the structural design of a hull. Would you be willing to do a little reading and certify the safety of the hull? That is where the proof of an opinion is: how much you are willing to risk by someone following your advice.
     
  14. rberrey
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    rberrey Senior Member

    Gonzo , risk is a personal choice , and building a boat unsupported by the designer is a risk , an example are builders on the Buccaneer 24 build forum . I didn't plan on using mat on my build and Ed would not provide scant-lings other than what he spec , so in deciding what material to use I could have consulted a NA for scant-lings like Scuff did or or do the math myself . While Ed,s book says not for design ! , he provides in section 11 material wise all you need to calculate puncture resistance , toughness , and stiffness . After doing the math , comparing the layup to that of compatible designs , I took the risk on my own layup and ordered material based on my math , and I had a personal comfort level when I did so , others might not .
     

  15. rxcomposite
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    rxcomposite Senior Member

    That would be design. Plywood itself is a structural material and giving it a light coat of epoxy + fiberglass only makes it heavier to gain added protection from permeability and impact. Cored laminate is a design that is best left to somebody who knows how. It is not a substitute. Of course, the whole structure will be much lighter.
     
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