Advanced aluminium extrusions for boatbuilding?

Discussion in 'Metal Boat Building' started by simon, Jan 1, 2008.

  1. simon
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    simon Senior Member

    Seaspark,

    thanks for the links.

    Did you follow your idea with the barrier coat any further?

    How thick should the metal barrier be, so that it can withstand the abuse of daily use?

    Would it be better to have a thin metalic layer without structural purpose or making it thicker to take on some load, or even just use metal as the outer shell of the sandwich structure?

    Would the epoxy bonding of aluminium withstand structural loads? What about the product that West System is selling called G/flex Epoxy.

    http://www.epoxyworks.com/25/pdf/G-flex_Epoxy.pdf

    I can think of two ways to easily construct a hull:
    - hard-chined hull
    - something like the tortured plywood, or the cylinder mold approach.

    This way the panels can be fully or partly prepared with vaccum bagging or infusion and asembled afterwards. How join the panels so that the metal is connected throughout the hull?

    Any good input? This theme bugs me for a long time and would be interested in seeing a realistic ideas.

    Simon
     
  2. SeaSpark
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    SeaSpark -

    Have not found a metal yet that bonds easily with epoxy or polyester in a marine environment.
     
  3. SeaSpark
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    SeaSpark -

    Somekind of lapstrake construction with aluminum extrusions and non structural goo between the strakes has my interest.
     
  4. SeaSpark
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    SeaSpark -

    Simon:
    Seaspark:
    To explain a little further, i think the required etching before bonding will eat away to much of a thin alu film and is impractical on a large surface. The idea as a whole has many impracticalities involved and the problem of moister ingress in a good epoxy laminate is mostly a theoretical one.
     
  5. petereng
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    petereng Senior Member

    Hello Simon,
    1) To go back to your original question - You can have nearly any shape you want custom extruded in aluminium and use conventional welding to build your boat. It comes down to the shapes you want to realise.
    2) The problem with metal is acheiving compound curves. A company in australia built 35 foot sailing boat hulls using explosive forming. They had a concrete mould (in the ground) the shape of the hull. They welded flat pieces together that fitted into the mould roughly. They then filled the hull with water and couple of sticks of explosive and "BANG" the aluminium is formed to the mould shape. Then they fitted out the hull in the normal manner. This is advanced boat building in aluminium
    3) If you choose to build in fibreglass flat panel, you require thermoplastic flat panels with pigmented resin. So no painting required. You bond it with plexus, no preparation required.
    4) If you choose to build in fibreglass in a mould to get the shape you want then use pigmented resin (no painting required) use a high elongation epoxy (like they use in wind turbine blades for great impact performance) and use plexus to join it (no preparation required)
    5) You can mix and match aluminium with fibreglass or carbon or steel but I'd try to live in one world. Its much easier.
    6) I've been involved with thermoplastic/glass panels in trucks that outperform aluminium in impact and abuse. For floors and side walls, they get loaded and unloaded every day, scuffed by forklifts etc etc.

    Cheers Peter
     
  6. simon
    Joined: May 2002
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    simon Senior Member

    Peter,

    thanks for the interesting input.

    I would like to know more about the use of thermoplastics in boatbuilding. I have not heard of it before.
    - How does the thermoplastics's surface toughness compare to aluminium?
    - How would you suggest to setup a sandwich structure with thermoplastics? i.e. Thickness of the thermoplastics.
    - What would be the weight of such a laminate?
    - Do you have any experience with Plexus's products? Their website tells that they have got approval by Loyds.

    Simon
     
  7. petereng
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    petereng Senior Member

    Thermoplastics toughness is greater then aluminium. Consider how tough a PETE bottle is vs the same thickness bottle in aluminium or a polyethylene canoe. The thickness and weight would be the same as conventional thermosetting resins. The processing temp is from 150 to 300degsC, depends on the plastic used. For flat sandwich construction I'd build the skins then secondary bond them to the core. If the core had a suitable processing temp then it can be done in one shot which is preferred. Plexus produceses bonds which are stronger then the laminate. Many boat builders are now joining their stiffeners and bulkheads using this. Advantages are no preparation required and no taping over the join. Saves considerable time. Curing time is 15mins so very fast in production situation. Plexus fulfils survey requirements so must be OK.

    Peter
     
  8. simon
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    simon Senior Member

    Hello Peter,

    sounds interesting. Could you give me some hints where to start reading to understand more about the handling of thermoplastics.
    What are the size limits for panels and what is the procedure to produce large panels in a backyard workshop, or is this out of scope?
    After a quick glimpse at Wikipedia, I see that there are more than 40 types of plastics. What do you recommend for the use in marine environment?

    Thanks for your input

    Simon
     
  9. petereng
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    petereng Senior Member

    Size comes down to the size of your oven. Oven temp comes down to what plastics you want to do. An oven with 250degs is OK, same as your kitchen oven, fan forced but the size of the object you want to do.

    http://www.twintex.com/products/tw_product.html

    Here are some premade products and info as a primer.

    Peter
     
  10. simon
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    simon Senior Member

    Hello Peter,

    So if I want to build large panels like made for Kelsall or Hughes cats, I will need an oven of same length and width as the panels. This will be a huge oven or there any easier ways to produce them? Are there any ready sheets of large dimensions?

    Thanks

    Simon
     
  11. petereng
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    petereng Senior Member

    You make the biggest oven that you can and then join the panels/parts together.

    Peter
     
  12. simon
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    simon Senior Member

    Peter,

    I have found a website describing large thermoplastic panels with fiberglass reinforcement and sandwiching with core material, like honeycomb and foam.
    The sheets can be produced in width up to 2.69 m and lengths up to ~150m.

    http://www.cranecomposites.com/zenicon.asp
    http://www.azobuild.com/news.asp?newsID=1655

    Panels for kits could be prepared in one part. So it would be possible to make kits for chined hulls with thermoplastics outer skins.

    What do you think about this?

    Simon
     
  13. petereng
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    petereng Senior Member

    Hi Simon,
    Looked at the site, very informative. The skins have good engineering properties typical of high quality vacuum bagged or infused laminates. The plastic is polypropylene which is very tough, tougher then epoxy or vinylester resins and PP is less dense so they would be lighter overall as well. Bond with plexus or equivalent and it would be bombproff!! Nearly
    Peter
     
  14. simon
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    simon Senior Member

    Hello Peter,

    I would like to continue this interesting thread, but think that it should belong to the composite department. Shouldn't we start a new thread over there?

    I have tried to contact Crane Composites without reply.

    - Do you know of any other producers of similar products?
    - Are there economical ways to produce large Continuous Fiber Reinforced Thermoplastic Composites Panels?
    - Would it be sufficient to glue thermoplastic laminates directly to both sides of the core?
    - How could panels be structually joined and still have a continuous surface?


    Simon
     

  15. petereng
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    petereng Senior Member

    Simon,
    I have strated a Thermoplastic Construction thread in the boatbuilding area. I have answered your questions there.
    Cheers Peter
     
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