Boston whaler type hull building

Discussion in 'Boat Design' started by Mr. Wiggles, Jan 16, 2017.

  1. Mr. Wiggles
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    Mr. Wiggles New Member

    I'm trying to figure out how to build a one off boston whaler type sandwich hull. Like, aluminum/foam/aluminum sandwich. The idea is to have positive buoyancy and be basically "unsinkable". However, I'm not totally sure about the manufacturing process or what to spec as far as thickness for each material.

    Mind helping a newbie out with this particular issue? I'll provide as many details as are requested.
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Aluminium in direct contact with foam buoyancy materials that cannot easily be removed, makes repairs, especially involving welding (you will likely start a fire), problematic. That needs to be taken into account.
     
  3. ondarvr
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    ondarvr Senior Member

    And when used in salt water the foam tends to hold water against the aluminum hull, which can result in rapid corrosion.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Yes, poultice corrosion is another snag.
     
  5. upchurchmr
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    upchurchmr Senior Member

    You need to tell us the details of the boat.
    Most of us cannot set the sizes of structure of such a boat,
    Those who can are mostly professionals.

    No one can recommend sizing not knowing length width, total weight, useage - row boat, power boat, or sail boat and a lot more.

    You don't need to make an aluminum/ foam/ aluminum sandwich hull to be unsinkable.
    Separate buoyancy areas will do the same.
    Now you can just build your aluminum hull per normal practice.
     
  6. SamSam
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    SamSam Senior Member

    Boston Whaler make the hull and liner pieces in two separate molds. They clamp the two pieces together while still in the molds and then inject the foam in between.

    To keep the boats correct shape, the molds have to be heavily made to withstand the pressure of the expanding foam.

    https://www.youtube.com/watch?v=WNGx77-2WWI

    .
     
  7. Ike
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    Ike Senior Member

    As far as unsinkable aluminum boats go, the most successful ones I have seen use many air chambers. The USCG tested one back in the early 2000's and even though we drilled holes in half the chambers it still passed the flotation tests. Aluminum against foam is asking for corrosion. Aluminum normally doesn't corrode if kept relatively dry, but if you get moisture and oxygen against it it will corrode.
     
  8. Barry
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    Barry Senior Member

    Not wanting to be argumentative but many of the larger aluminum boat manufacturers in the Pacific Northwest spray foam much of the inside of their hulls with foam. Certainly hull repairs, ie welding could be a pain but I have yet to see corrosion issues and many of these boats are at the 20 year mark
    I suspect that with proper surface prep and the proper non permeable foam, this might not be a big issue.
     
  9. ondarvr
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    ondarvr Senior Member

    These are the exact boats that have issues, some are in very bad shape. check local forums on the subject. Not every boat is affected, so one boat may be OK, and the next has holes in it.

    In a perfect world if you could afford the correct prep and find a non permeable foam it may help, but the issue is water between the foam, or any material that comes in contact with the aluminum. If there's a lack of oxygen along with water it forms a very acidic environment, add salt and it gets worse. Put anything in the bilge that creates an environment like this and you have a potential issue.

    a quick search found this

    http://www.ifish.net/board/showthread.php?p=1100878
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    Presumably proper priming/painting before installing the foam would help.
     
  11. Ike
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    Ike Senior Member

    I used to participate in the Metal Boat Society forum. There was ongoing discussion about this (using foam as insulation on metal hulls). I think the consensus was that with adequate prep the foam could be used for insulation, but that it would not last forever and eventually have to be taken out. The inside of the hull would have to cleaned up, prepped and the foam re applied. But what our poster here is proposing is flotation foam. It would not be accessible for inspection or replacement.
     
  12. upchurchmr
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    upchurchmr Senior Member

    Actually the OP wanted aluminum/ foam/ aluminum sandwich.
    I personally have never seen that sandwich construction.
    Seems much harder than anything I've known about.
    And of course it "would not be accessible for inspection"
     
  13. PAR
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    PAR Yacht Designer/Builder

    I've seen aluminum foam core panels used in aircraft, but never in a boat.
     
  14. endarve
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    endarve Junior Member

    Yep, on aluminum and steel. Most of the reason for foam inside the hull of a metal boat is insulation to prevent condensation and reduce corrosion.
     

  15. upchurchmr
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    upchurchmr Senior Member

    PAR,

    Not to disagree, I'm just interested - what aircraft?
    Were these flat panel type panels?
     
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