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My Answer.

Benefits: The major advantage of aluminum in ship building is its strength to density ratio. Aluminum has high tensile strength with less weight, which results in lowering the weight of the overall structure and thus reduce the fuel cost. When aluminum is exposed to air, a positive layer of oxide is formed on the surface which makes its corrosion resistant. Also, it is easily available in many standard forms as third most abundant metal, and can be transformed to all shapes

Disadvantages: i am seeking formal statements on what are some possible disadvantages of aluminum alloy as a replacement of steels in ship building.

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    $\begingroup$ Not sure if a boat would flex enough but aluminum will fatigue with any flex. Much harder to fabricate with aluminum. $\endgroup$
    – paparazzo
    May 4 '18 at 14:09
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Advantages:
  • Makes a lighter craft. However this is only significant for small fishing boats, canoes, punts, where they are lifted out of the water by hand. I can see possible uses in warfare where weight may be critical. In normal use the main energy cost of shipping is water friction. A ship's weight is small compared to it's cargo's weight. Reducing a ship's weight to zero wouldn't change the operating costs. (You see references to ships traveling in ballast -- part of the cargo compartments are filled with water so that the ships handles properly.)
Disadvantages:
  • Expensive raw material.
  • Expensive fabrication. Requires special techniques to weld.
  • Flamnable. (See HMS Sheffield in the Falkland's war)
  • Corrodes rapidly in salt water. (In air or in fresh water aluminum skins over with an oxide layer. In salt water this layer doesn't form, or is removed as fast as it forms.
  • Softer than steel. Parts exposed to casual friction (freight moving) would wear faster.
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  • $\begingroup$ The always accurate Wikipedia says this about the HMS Sheffield: "The sinking of Sheffield is sometimes blamed on a superstructure made wholly or partially from aluminium, the melting point and ignition temperature of which are significantly lower than those of steel. However, this is incorrect as Sheffield's superstructure was made entirely of steel." $\endgroup$
    – Wasabi ♦
    May 3 '18 at 17:39
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Marine aluminium is 100 times less prone to corrosion than steel. source link : https://www.aluminiumleader.com/application/transport/ (Not sure about Marine Aluminium vs stainless steel though) For Ships, strength to weight is ratio is not a big deal. But corrosion resistance is. Imagine a ship which doesn't get corrode even after 100 years.

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  • $\begingroup$ Nonsense ! per NACE Certified Corrosion Specialist # 1635. $\endgroup$
    – blacksmith37
    Dec 19 '19 at 15:38
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Aluminum is much more expensive than steel. Note here that the dead weight of a ship is not an important factor in its cost of operation, which means that the weight savings achieved by buying aluminum instead of steel are not paid for by fuel savings.

The only arena in which the weight savings associated with building the hull of a boat out of aluminum are important are those in which the boat is loaded and unloaded from a trailer by muscle power.

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Aluminium corrodes in seawater that is why it is used as sacrificial anodes on steel. It is more difficult to weld than steel and almost impossible to develop good mechanical properties in large weldments. Aluminium may not have ever been tested for toughness in the heavy sections (eg. 6 in.) needed for ships and I expect low toughness would result in ships breaking in half like the WW2 Liberty Ships....And it would be very difficult/expensive to cut thick plate sections for hull fabrication; You can shear or saw it but the logistics would be much more expensive than the torch cutting used for steel.

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  • $\begingroup$ What ships, other than battleships and icebreakers, use 6" plate? Supertankers use about 1", and the vast majority of all shipping uses thinner stuff. But I can buy 12" al plate off the shelf, so I think it is a known quantity. And these folks don't seem to have problems cutting it. Outside the third world, Torch cutting isn't much used for ship plate production. $\endgroup$
    – Phil Sweet
    May 4 '18 at 3:11
  • $\begingroup$ They use ! " STEEL , that requires about 3" Al in plain hull plate. Heavier plate is used in the keel and along the top hull corners So I expect there where Al , 6" is a possible requirement. When you cut on a shear the plate must be moved to and manipulated for the shear, as the sheart is too massive to move. No problem for a couple plates, but a great expense if you are cutting hundreds of plates for a large hull.. $\endgroup$
    – blacksmith37
    May 7 '18 at 3:03

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