Glassing over foam core questions.

Discussion in 'Materials' started by member 64267, Apr 19, 2018.

  1. member 64267

    member 64267 Previous Member

    I am designing a small hydrofoil and would like to know from the communities perspective the potential benefits and downfalls of my design and method of construction. My plan is to design the hull in rhino and then machine it out of a ridgid foam and glass over the entire structure. I plan to reinforce stress points and add strength by cutting the machined foam core and adding ribs but I want to leave most of the foam in place. 1 benefit I can see is having a continuous fiberglass Hull with no seams and no form to build.
    The basic concept of the boat is a tandem sea kayak with 2 small outriggers forward, self adjusting t-foils. What do you think?
  2. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Welcome to the forum.
    Good luck with the design. There are many here who will gladly assist your use of Rhino.

    Your proposed build technique will result in a heavy craft. You describe a single fiberglass skin over a foam form. In this sinerio, the fiberglass must be very thick because the foam is non+structural. Strong lightweight boats can utilize FG-foam-FG sandwich construction. The two thin FG skins interact with each other and the foamcreating a rigid structure.
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    You haven't offered any idea of scale, but monocoque hulls are fairly commonplace. As Blueknarr points out, there is glass on both sides, though. It sounds as if your ribs are planned as insets. Ribs would not generally be needed if you glass both sides. Thus it seems the ribs are not a good idea. If you inset them, the foam would be weak at the inset as the core thickness varies. A tandem sea kayak would not require outriggers as each kayak is essentially an outrigger to the other kayak.

    Rigid foam is fine as a construction material; despite it being unpopular with boat builders. It has its place as a low cost option. I built two outriggers for a canoe with rigid foam; encased them in light glass and epoxy and they are a superb lightweight, durable product with epoxy.

    Your method, however, needs some tweaking. And I have never tried to shape something as large as a kayak. I don't quite understand how you expect to achieve fair lines without some type of form. Nor do I see it practical to machine the inside of the structure if the foam block is solid to start. If you machine the foam in sections; you would still need to glue them together somehow and make sure the CL and WL remain true. The foam would also need to be rather thick in order to achieve stability without glass at the start in a formless build and the thicker glass would require a larger kayak for the same space on the inside.

    Hope this helps with the 'project'.
  4. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Much more information is needed before anyone could intelligently comment on your design concepts.

    Back to foamcore

    Multitudes of one off boats have successfully used foam panels flexed to a jig for their primary construction technique.

    I don't have enough information about your project to give definitive advice. Consider the following:
    Pre-glassing one side of foam panels
    Set panels in female jig glass inward
    Tab seams
    Remove from jig
    Shape exterior
    Glass, fair, paint
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  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    It seems, you're self designing a "hydrofoil", whatever you may mean by this, which has some obvious questions in itself and also self engineering this puppy, with little understanding about the material properties and methods in either approuch. Have I got this about right? How far from shore can you swim back too? Composite and sandwich core structures have to be fairly well engineered or bad results will likely occur, so maybe a little dimensioning needs to be applied, before any reasonable answers should or could be offered. We can offer the "Cliff's Note's" version of common methods and solutions, but do these logically apply to your "hydrofoil". Simply put, how about enough detail in the project that someone can actually get an idea of what you're up to, besides a single sentence of something that out of hand sounds "draggy", at the very least, particularly for a foil borne craft.
  7. gonzo
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    gonzo Senior Member

    I think that before even discussing about the structure, the big question is how does the OP intend to generate enough thrust with a paddle to get a catamaran kayak up on plane.
  8. ThomD
    Joined: Mar 2009
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    ThomD Senior Member

    That method of construction is reasonably common in aircraft, and Chris White built his proa that way. Meaning foam blocks glassed. And of course surfboards. He says machine, some aircraft guys have CNC machines that will take the pieces. I am talking about backyard guys. Then there is the hot wire method. I did a board that way for a tri.
  9. member 64267

    member 64267 Previous Member

    Hi every one thanks for your replies and interest. Are you familiar with the k2 kitefoiler? Let me see if I can get more specific on the important parts of my design. I would like my finished product to be a 22 ft kayak monohull with forward outriggers. 2 forward foils attached to the outriggers, rear foil at the transom. I like Ray Vellinga designs of t foils with ailerons and the trailing mechanism for self adjusting angle of attack but I am not sold on the mechanics of the linkage systems. I am open to all options but I really want the angle of attack to be self adjusting.
    For the hull I intend to machine it from rigid foam block on my friends 3 axis router and use a single 1/4 in glass layer over the foam. I’m aware of the weight this will add and I know I need to do my math for volume of glass and foam to get the total weight of the craft. light is not my main priority as I need it to be strong enough to slam around in rough water in the Puget Sound and straight of Georgia. I have 2 6 hp Suzuki outboards and I need to find a way to either lower the engines on a bracket for take off or a method for extending the shaft. I hope to achieve 3 feet of altitude carrying the boat at (estimated) 300lb and 2 passengers at 500 lbs useful payload. So fully loaded around 800lb. But back to the engines. I’ve considered using a 18 v drill motor to raise and lower the engine bracket but lengthening the shafts would be more ideal I believe. I want this boat to be as simple as possible while achieving safe and consistent lift. I’ve built kayaks and small wood sailboats with my father and we are building this project together. He is getting older and we have always wanted to build a hot rod together so this is me and my dad building a hotrod. Her name will be angel of attack. Hopefully she’ll be a low flying demon on the water and pull 40+ knots. In the future I want to switch to torqueedo drives and also if it turns into a commercial venture green just sells better. I need to get my drafting suite setup on my iPad but as soon as I do I’ll be able to upload images of my design and material specs. I don’t want to burn you guys out with pipe dreams and Imaginary designs as I am well aware that these forums can be pretty harsh when inquiries aren’t properly worded or directed. I enjoy the benefits of having thousands of like minded individuals interested in making cool boats.
  10. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    I like the sound of that.
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  11. member 64267

    member 64267 Previous Member

    2 6hp Suzuki engines for now. Most likely heavily modified. I plan on casting shaft extensions if it’s not possible to buy what I need and if it’s feasible.
  12. member 64267

    member 64267 Previous Member

    I just talked to a friend with an automated 20’ breakpress he just did boats for the first time last week. He’s about to make twenty 16’ skiffs. This could get wild real quick. Ditch the glass and foam and go aluminum all the way!?! I have a foundry and a large sheet metal shop at my disposal. I could cast my wings even. Must calculate mass and volume of materials. As I understand the existing profiles Are readily available but the area needs to be customized to your weight and desired speed and lift. faster and lighter =smaller wings bigger and slower =larger wings. But there is always an optimal size that is decided through a calculation containing all these variables right? Is it ama and naca profiles to choose from? This will really be my biggest hurdle is learning to customize my optimal wing area and profile.

  13. member 64267

    member 64267 Previous Member

    That is a totally reasonable option. Thanks
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