Aluminium Boat, Small, Thin,Unwelded, Fiberglassed?

Discussion in 'Metal Boat Building' started by kdifzero, Aug 18, 2021.

  1. kdifzero
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    kdifzero Junior Member

    Morning all,

    As the title says what make of my idea using 1mm reg aluminium (I can get it cheap) cnc cut parts which would be carbon epoxyed together (no welding at all), and then both sides of the hull being fiberglassed.

    Would this work on a small boat and or maybe upto 30ft?
  2. bajansailor
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    bajansailor Marine Surveyor

    Welcome to the Forum KDI.
    The mere fact that you probably cannot find anything with Google re your proposed construction method should speak volumes (I presume that you have googled it?).
    Re 'carbon epoxying' the aluminium sheets together, I am intrigued - how is this done?
    When you say 'fibreglassed', do you mean with polyester or epoxy resin?
    I think that you would be better off using proven construction methods with either plywood, foam or strip planking rather than trying to encapsulate thin ally sheets in fibreglass.
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  3. Ad Hoc
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    Ad Hoc Naval Architect

    following on from Bajansailor....

    Not to mention carbon and aluminium do not mix very well at all.
    You would need significant isolation to prevent corrosion and to ensure the barrier is never breached too!.
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  4. Rumars
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    Rumars Senior Member

    If you want to do a glued aluminium hull, it's possible, as is using 1mm plate. Lots of work to do it right, but that's your choice. By "regular" Al I assume you mean some common alloy like 3003, it depends if you use the boat in "regular" water or not.
    Fiberglassing 1mm Al sheet is nonsense, waste of time and money.
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    And whenever you can say " which I can get cheap" there always seems to be a catch ! The first catch might be it is an alloy quite unsuitable for salt water.
  6. kdifzero
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    kdifzero Junior Member

    Hi thanks for having me, to expand upon my genius some more over on talkcomposites been mentioned that you can use carbon fiber filler plus resin to bond two pieces of aluminium together, makes a better "weld" so to speak as actual welding due to heat can cause damage in comparison.
    When I say fiberglassed yes basically epoxy inner and outer hull.
    I get sticking with traditional methods but this stuff is so easy to work with, and no there is no mention on google but that might be because father googles algorithm has been waiting on me all along..... thank you for responding.

    Would the fiberglassing not help with that?

    I understand but 4mm is way more expensive and welding is not a cheap thing, these are compromises.

    I would imagine so, but isnt all aluminium?
  7. bajansailor
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    bajansailor Marine Surveyor

    Lots of good advice above KDI.
    Re the above quote, you mention for boats up to 30' - this is not exactly 'small' relatively.
    First of all - what do you want to use this boat for?
    The important thing to do before even thinking about construction materials is to determine your Statement of Requirements (SOR).
    This will drive everything - hull size, shape, material, construction method.
    Can you describe what your intended usage will be?

    You also mention
    Depending on what your SOR says, the odds are good that you will find an existing secondhand boat (not necessarily aluminium - it could be fibreglass) that can do the job for you, at a fraction of the cost of building a new boat.

    On the contrary - there are many different grades of aluminium, including specific marine grades - and for boatbuilding you should only use marine grade aluminium.
  8. duluthboats
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    duluthboats Senior Dreamer

    Build a simple test model. Bond 2 small sheets together, sandwich them in glass and epoxy. Subject them to some flexing and temp changes. I think you will find that the composite will quickly delaminate, causing complete structural failure. The 1mm aluminum adds nothing, it just creates problems.
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  9. kapnD
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    kapnD Senior Member

    If your use of the aluminum is simply to define the shape of the fiberglass applied over it, there are many ways to create an armature that will be cheap and effective, without the obvious problems of an aluminum core.
    A mold, male or female, can be constructed from almost anything, including, but not limited to, plywood, foam, plaster, drywall, paper mache, shrink wrap, or even aluminum, and separated from the layup by a mold release membrane.
    I’d recommend NOT using a core at all, solid fiberglass is simple and effective, and can still be cored with an acceptable material where/if it is deemed necessary.
    As mentioned above, an SOR is a definite prerequisite to having a serious discussion.
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  10. upchurchmr
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    upchurchmr Senior Member

    Aluminum as a core is almost the absolute worst material to use.
    Steel would be worse.

    Aluminum is difficult to bond unless you use a specific technique.
    The thermal arguement has real merit since I did something similar and the glass/epoxy and aluminum separated when I set it out in the sun. No load.

    Look at normal kayak strip planking methods. That will be cheaper than any thickness of aluminum unless you are stealing the metal.
    1mm is not enough thickness to make a useful sandwich.
    1/4" cedar or other wood works better and weighs much less with better strength and weight. As far as I remember.

    Best suggestion after the cautions is to make a test sample and destroy it. Or make multiple samples and destroy them in different ways.
    That way you don't have to listen to know-it-alls (me) and can do what you want. Won't cost much and will be real experience/ knowledge you can use.
  11. rxcomposite
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    rxcomposite Senior Member

    Google will have to wait forever.

    While gluing (bonding) aluminum together has worked well in racing cars and aerospace, sheathing aluminum with glass fiber laminate, physics just does not permit it.

    Aluminum has a much higher modulus than glass laminate. The idea is high modulus/higher strength fiber is placed on the outside and lower modulus/lower strength element is used as a core.

    Not to mention the internal stress it will create because of the difference in coefficient of thermal expansion. Just varying heat from the sun will cause the different material to pull away from each other. You will have delamination over a period of time.
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  12. DCockey
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    DCockey Senior Member

  13. KeithO
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    KeithO Senior Member

    Whats wrong with using solid rivets, you know the way airplanes and the like are built to this very day ? Yes, sealant can be used to prevent leakage at joints, instead of adhesive.
  14. DCockey
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    DCockey Senior Member

    We own an aluminum skiff built by Lund when is rivitted together. My guess is millions of aluminum boats have been built with rivets.

  15. gonzo
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    gonzo Senior Member

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