Let's make them cheaper by building them of more expensive materials

It is possible to wonder where some people got their education – even, if they did. For example, it is being seriously suggested that we’d all save money if only we built ships out of aluminium instead of steel. Aluminium costs more than steel – some four to five times more in fact. So quite how this will save money isn’t obvious.

But here it is, here’s the assertion:

Because of the wide availability of cheap (and often dirty) fuel, shipping has traditionally been wasteful. Most merchant ships are made of heavy steel rather than lighter aluminium,

Well, the basic cost of aluminium is that several times that of steel. So, obviously, it’s not all that likely that the fuel savings from the lighter weight are going to be worth it.

We’ve even an interesting test of the proposition – if it were then more ships would be built of aluminium in order to gain the fuel savings, wouldn’t they?

But it’s worse than this for of course it is. The usual mistake of thinking only about emissions from operation, rather than total system usage, is being made.

Each tonne of aluminium – it’s a rule of thumb but a useful one – incorporates $900 of energy. That’s just what it costs in order to turn aluminium oxide into aluminium. Steel, given its lower price in total, quite obviously incorporates less energy than this.

So, the suggestion is that we should be using more energy in our system in order to save energy then, is it?

And people wonder why no one in the metals or mining world takes a blind bit of notice of the environmentalists, do they?

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  1. Aluminum ships…in salt water? What could go wrong?

    Cheese is even lighter than aluminum, and that is what our ships should be made of.

    “shipping has traditionally been wasteful”? Show me a case where shipbuilders willfully wasted money they could have saved. Or does the author mean they “wasted” energy? No, they spent it, to get a desired result.

  2. Ummm…
    What’s the major dissipator of energy in moving a classical large ship?
    Strangely, a quick Goog doesn’t provide an umabiguous answer.
    They all talk about reducing wave-making by constructive interference from bow-bulbs, and the like
    Almost as if the mass of the hull was inconsequential…
    So further work to see if there’s any info on (eg) the average displacement (= mass of empty ship) for container ships. Nope. Lots of info on L W D and TEUs, but no displacement. The only thing I found was this note about what seems to be a successor to the WW2 Liberty ships :”The total weight of the ship and everything in it is the displacement, measured in long tons of 2240 lb. A long ton is only a little larger than a metric ton of 1000 kg, but is considerably larger than the U.S. short ton of 2000 lb. The displacement of the AP2 is 15,200 tons. This weight displaces 532,000 cubic feet of sea water weighing 64 pcf, and loads the ship down to the normal water line. The deadweight is the difference in displacement when the ship is completely unloaded, of cargo, fuel, crew and so forth. The cargo deadweight is the weight of the cargo alone. For the AP2, the deadweight is 10,800 tons. Therefore, the weight of the ship alone is 15,200 minus 10,800 tons, or 4400 tons. The reference does not give the cargo deadweight of the AP2, but if it is in the same proportion to the deadweight as the net tonnage is to the gross tonnage, it would be 6673 tons. Most of the difference would probably be fuel.”

    That is, for a relatively small ship (ratio should get better with increasing size), the ship mass was ~30% of the loaded ship. making small percentage changes in that mass won’t have enormous effects on the total moving mass – even if that mass is the important factor in fuel consumption.

  3. The vast majority of the energy consumed moving a ship from place-to-place is that needed simply to push the thing through the water – which is by-and-large a function of drag. OK, a lighter ship will need less energy to accelerate it to cruising speed (and decelerate it at the other end of the voyage) but as the time taken to reach cruising speed is negligible in comparison to the voyage duration (unless we’re talking cross-channel ferries, and even then they’re up-to-speed in a few minutes), there’s not going to be much gain. Add to that the cost of building in aluminium and its relative delicacy in comparison to steel it’s going to need a lot more maintenance and be far more susceptible to damage – either from flotsam or docking procedures.

    Bl**dy silly idea.