Large aluminum hulls.

Discussion in 'Boat Design' started by lbdm, Jul 1, 2019.

  1. lbdm
    Joined: Jul 2019
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    lbdm New Member

    Hello,

    I got some interest on boats/yachts recently and I learned about the advantages of aluminum hull, but when looking on those 100m+ yachts I never found one with aluminum hull.

    Is there a technical reason (other than costs) for that? Or, do the costs become exponentially higher when reaching those large dimensions?

    Tank you.
     
  2. jehardiman
    Joined: Aug 2004
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    jehardiman Senior Member

    It becomes a strength to stiffness to weight to cost issue. Once the vessel becomes "large" (YMMV), aluminum's modulus and poor post weld strength requires more material and deeper sections, resulting in poorer structural performance (i.e less strength or stiffness per unit cost or weight or volume). Economics and engineering needs vary so there is no hard and fast line. while you won't see a "large" tanker made of aluminum, you will see a weight sensitive fast ferry made of it.
     
  3. Ilan Voyager
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    Ilan Voyager Senior Member

    The main reason is cost. On a big monohull there is no good reason to enter in the complications of aluminium for the hull itself. The engineering of a steel mono hull is straightforward, it can be built simply and cheaply with steel. For the superstructures is another matter. Often the hull is in steel and all above the deck is in aluminium where the gains of weight matter really for the stability.
    The combination steel hull and aluminium superstructures is now common on yachts, cruising ships and ferries.
    The all aluminum is reserved to fast multis catamarans and trimarans where the total weight really matters because of the enormous surfaces of hulls implied. The biggest all alu boats of the present time are the 100m and more trimarans by Austal.
    [​IMG]
    A little precision the alu boats use 5xxx series alloys which are not very affected by the HAZ of welding. For the 6xxx series used in bicycles for example it's another song.
     
  4. lbdm
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    lbdm New Member

    @jehardiman and @Ilan Voyager,

    really thank you for your replies. These are the reasons I thought but you put them in a very more professional terms. :)

    I side question: in average how much more a aluminum hull cost in relation to a steel one? 30%, 50%, 200%

    Thank you.
     
  5. jehardiman
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    jehardiman Senior Member

    There is really no hard and fast comparison other than to say they cost more. First of all, more than half the cost of a hull is in fabrication, not material. Aluminum plate is about 3 times the cost and about 1/3 the weight of the equivalent thickness of steel. However aluminum's yield is ~2/3 of steels so you need ~ 1/3 more thickness for direct 1:1 replacement. For this reason, aluminum hulls are not designed like steel hulls. Aluminum hulls are designed to use more structural support members and thinner sections which lowers material costs but drives up fabrication costs. Actual cost premium would depend on comparing two fairly detailed preliminary designs.
     

  6. lbdm
    Joined: Jul 2019
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    lbdm New Member

    Thank you. :)
     
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