aluminum and composite hull

Discussion in 'Materials' started by boatgm2, Dec 19, 2020.

  1. boatgm2
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    boatgm2 Junior Member

    I want to use aluminum in the hull, rubs and bow stem and composite topsides. Does anyone have experience with such?
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Could you elaborate a bit more about your proposed design please?
    Are you proposing an aluminium hull below the waterline, and composite above?
    How are you proposing to join the aluminium to the composite sections?
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I think he means the hull in alloy, the deck and cabin in glass, if so that has been done by some builders, probably to get a more pleasing appearance with the upperworks.
     
  4. boatgm2
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    boatgm2 Junior Member

    I am early in the project but like the toughness of alloy under the waterline, integral tanks and alloy equipment foundations. Somewhere above the waterline I envision an alloy channel that the composite topside panels can be bonded into. My first thoughts were to also have an alloy bow stem and alloy rubs.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm not seeing much advantage in mixing it up like this.
     
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  6. bajansailor
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    bajansailor Marine Surveyor

    Me neither - you would be much better off in every way imaginable by building the whole hull in aluminium.

    Even a composite deck (on aluminium beams and longitudinal stiffeners underneath? ) is unlikely to offer any advantages over an aluminium deck.

    However there could be merits in a composite superstructure, especially if you want to have some nice curves in it.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    If you a have an alloy frame and bottom sheets, it is logical to do the topsides the same way, certainly you will have an "unusual" boat doing it your way, but the valuation would be well down,
     
  8. boatgm2
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    boatgm2 Junior Member

    thanks
     
  9. gonzo
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    gonzo Senior Member

    Are you referring to fuel tanks? They should be separate from the hull.
     
  10. Barry
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    Barry Senior Member

    How naive we were 25 odd years ago when we built our first aluminum river jet boat. At the time, and to this day the bulk of aluminum jet boats ( base line 18 - 24 foot inboards) had a very small
    foredeck, a windshield and open cockpit. From the usage that we wanted the boat for, extended overnight exploring trips we wanted a covered cuddy for sleeping.
    We contacted a fibreglass boat builder and purchased the top section from one of his boats. Built the bottom in aluminum, joined the two. Unfortunately, our "perfect" concept of a jet boat was just that, "our perfect" jet boat. We did sell it but then decided to follow the mainstream and changed back to a more traditionally accepted form.

    Most fibreglass boats have the top shell and the bottom shell joined by riveting or bolting using an extruded aluminum gunwale strip with a rubber insert to cover the bolt heads. Most larger marine distributors will have this in various strengths. There will be about a 3/16 inch offset to allow the top to rest in and then the top and bottom are bolted at about 4 - 6 inch bolt centers. I would recommend a 3/16" 316 ss, nylock, larger washered
    combination. At the joint, the composite piece would have about 1 inch to 1 1/2 vertical leg and on the aluminum hull the same.
    We used silicone as a sealant but I would suggest a marine sealant instead. Silicone has its place but there are better for this application.

    We did it for the express purpose of getting a large cuddy and having smoother lines that what we could have built without many many hours of aluminum work.
     
  11. ondarvr
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    ondarvr Senior Member

    It's not uncommon on large yachts, the hull is steel and everything above that is composite, frequently carbon to reduce weight.
     
  12. kapnD
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    kapnD Senior Member

    Aluminum framing covered with lightweight fiberglass/plywood is workable. 9E6DD109-42D1-4280-AD3E-179F13BDB7E9.jpeg BD7AD0C4-34ED-4E81-A112-16187EF3CAF1.jpeg E7CC263D-DBD4-45BC-8733-1D3F979CDD7B.jpeg Here the roof is aluminum tubing frame with Herculite stretched over, the whole cabin/roof unit is under 500#. (This is in the tropics, no insulation was even considered!)
    I’d suggest that the OP utilize aluminum deck framing and decking to unitize the important hull/deck structure, then do as he pleases with the superstructure.
     
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  13. fallguy
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    fallguy Senior Member

    It must not be forgotten that an aluminum cabin requires insulating; a composite cabin does not.
     
  14. Mr Efficiency
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    Mr Efficiency Senior Member

    Nothing wrong with the idea of an aluminium hull, with GRP superstructure, but in this instance, as I understood it, he wanted to start the GRP from the chine up. He only speaks of alloy "bottom sheets"
     

  15. Kayakmarathon
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    Kayakmarathon Junior Member

    Avoid bonding a carbon fiber lay-up to a metal. There will be a galvanic reaction between the two dissimilar conductors. A fiberglass layup can be bonded directly to aluminum since fiberglass in not a conductor. So when a carbon part is bonded to a metal part, a layer of fiberglass is laminated between the carbon and metal to prevent a galvanic reaction.
     
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