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Cost is indeed the core issue. It's an issue with most synthetic fuels and it's not an issue that is likely to go away. As long as that means you have to pay a

Cost is indeed the core issue. It's an issue with most synthetic fuels and it's not an issue that is likely to go away. As long as that means you have to pay a steep premium to be green, it's not going to be popular. International agreement on carbon taxes is unlikely. And most ships operate in international waters under the flags of countries with favorable taxes and rules (e.g. Panama, Greece, etc.). With shipping, shooting for perfect is really expensive. But we're starting with a status quo that is really bad that can be improved upon. For example, most ships are made out of steel. Steel is relatively heavy. There's a ship yard in Tasmania working on a battery electric 300meter long ferry made out of aluminum. They've built dozens of aluminum ships already. Aluminum is much lighter than steel and that cuts the amount of energy needed to move it around by about half. That's nice because batteries are expensive and don't provide a lot of range. But making ferries out of aluminum is of course something that could work for any kind of ship. Fuel is really expensive. 50% fuel savings are very attractive to ship operators. Most ships burn bunker fuel. That's properly nasty stuff. So using only half of that would be an improvement. It's toxic, causes lots of pollution and is nasty if it gets in the water. Some cruise ships run on LNG these days. Much cleaner but it takes up space. Those ships are mostly still made out of steel. If you make them out of aluminum, they'd be a lot lighter probably and use less fuel. So smaller LNG tanks, less CO2 emitted, and more space for the passengers. Win win. There are also some interesting things happening with composites and carbon fiber. That stuff is even lighter and there are some companies focusing on marine applications as well. So, we could cut weight and fuel usage of ships by using modern/different materials. There are some experiments happening with using sails on ships to cut fuel usage further. If you add all this up, we could be cutting fuel usage significantly (40-70%) and make the emissions problem a lot smaller. And unlike synthetic fuels, this also translates into financial savings. So that means it's more likely to happen. And if we eventually put batteries in these ships, they'll go a bit further as well. It's not perfect. But probably a lot better.

pjc50 2y ago
> Aluminum is much lighter than steel and that cuts the amount of energy needed to move it around by about half. Hmm. I'm suspicious about this - might be true for cars, definitely true for planes, but ships sit at neutral buoyancy, most of the mass is cargo, and the main component of energy expenditure is actually drag. So there's significant benefits to low drag hull designs or "slow steaming", but the actual ship material isn't terribly high up on the priority list. And aluminium is way more expensive.
- kragen 2y ago
  I think aluminum is mostly more expensive than steel because energy is expensive, but solar energy makes energy cheap. If a ship's mass were mostly ship rather than mostly cargo, making it out of a heavier material would increase its water displacement, which would increase its drag. I don't know if that's a proportional effect; I think it's actually sublinear. But, since most of the mass is cargo, it won't make much of a difference. If most of the mass weren't cargo, you could ship things more cheaply by sealing the cargo in giant plastic bags and towing it across the ocean behind a tugboat.
  - throwup238 2y ago
    Both steel and aluminum production depend mostly on the cost of energy, so any improvements that would make aluminum cheaper would also make steel cheaper. Steel also has the benefit of being ferromagnetic so it’s a lot cheaper to pull scrap steel out of the garbage stream and recycle it, but that depends on having lots of scrap steel to begin with. There’s really not a lot of room to make aluminum as cheap as steel, as all economies of scale have by now been mostly realized. The cost of energy is so dominant that it makes sense to run smelting plants idle most of the time with the crucible heated constantly just to take advantage of negative power prices (although there are other factors at play like subsidies and national security concerns). Barring some sort of seismic scientific breakthrough in metallurgy, the current ratio of 2-3x the cost of steel is here to stay. There’s maybe a little room if we reach “peak aluminum” as the fraction of recycled scrap approaches 100%, but I don’t think that would make that much of a difference because we’re likely to hit “peak steel” before then (and again, its just easier to recycle from a logistics standpoint).
    - kragen 2y ago
      Hmm, really? I didn't realize that. Thank you!
bluGill 2y ago
aluminum has terrible metal fatigue issues. Ships that have been perfectly fine for years will suddenly just fall into pieces. Trucks where weight matter do often use aluminum trailers, but they keep careful track so they are scrapped before they fall apart. This fall about is not something an inspection will catch (not 100% true, ultrasound and other inspection methods will catch some of this, but for discussion it is close enough to say you just scrap aluminum before it fails instead of inspecting) That isn't to say aluminum can't be used for ships. Only that it is tricky.
- jillesvangurp 2y ago
  There are different alloys of aluminum with different properties. Just like steel. And of course it's been used in the aviation industry for a long time as well. Car manufacturers are using aluminum castings in cars these days. And there are engine blocks made out of aluminum as well. Anyway, this is the ship yard I mentioned. They have a few decades experience making ships out of aluminum: https://en.wikipedia.org/wiki/Incat https://en.wikipedia.org/wiki/Incat
  - AceyMan 2y ago
    As I understand it, the gotcha with aluminum is: there is no such thing as non-fatiguing stress — whereas, say, steels, have a range of elasticity where it can operate and not lose strength (or get cold-work hardened). With aluminum, any flexion — no matter how little — marginally reduces the strength of the material. Ergo, even under ideal conditions it's saddled with a limited service life.
    - HPsquared 2y ago
      You just design it so the stress in the material gives a very long fatigue life (as in, how many zeros do you want?). It doesn't have a defined "fatigue limit", but it may as well have.
LgWoodenBadger 2y ago
I don't understand how an aluminum structure can withstand the stresses in bulk-oriented ships without fatiguing to destruction in the first rough weather.
- HPsquared 2y ago
  You make it thick enough so the material isn't stressed. This does require rigorous engineering processes, but it's pretty common.

pjc50 2y ago

> Aluminum is much lighter than steel and that cuts the amount of energy needed to move it around by about half. Hmm. I'm suspicious about this - might be true for cars, definitely true for planes, but ships sit at neutral buoyancy, most of the mass is cargo, and the main component of energy expenditure is actually drag. So there's significant benefits to low drag hull designs or "slow steaming", but the actual ship material isn't terribly high up on the priority list. And aluminium is way more expensive.

kragen 2y ago
I think aluminum is mostly more expensive than steel because energy is expensive, but solar energy makes energy cheap. If a ship's mass were mostly ship rather than mostly cargo, making it out of a heavier material would increase its water displacement, which would increase its drag. I don't know if that's a proportional effect; I think it's actually sublinear. But, since most of the mass is cargo, it won't make much of a difference. If most of the mass weren't cargo, you could ship things more cheaply by sealing the cargo in giant plastic bags and towing it across the ocean behind a tugboat.
- throwup238 2y ago
  Both steel and aluminum production depend mostly on the cost of energy, so any improvements that would make aluminum cheaper would also make steel cheaper. Steel also has the benefit of being ferromagnetic so it’s a lot cheaper to pull scrap steel out of the garbage stream and recycle it, but that depends on having lots of scrap steel to begin with. There’s really not a lot of room to make aluminum as cheap as steel, as all economies of scale have by now been mostly realized. The cost of energy is so dominant that it makes sense to run smelting plants idle most of the time with the crucible heated constantly just to take advantage of negative power prices (although there are other factors at play like subsidies and national security concerns). Barring some sort of seismic scientific breakthrough in metallurgy, the current ratio of 2-3x the cost of steel is here to stay. There’s maybe a little room if we reach “peak aluminum” as the fraction of recycled scrap approaches 100%, but I don’t think that would make that much of a difference because we’re likely to hit “peak steel” before then (and again, its just easier to recycle from a logistics standpoint).
  - kragen 2y ago
    Hmm, really? I didn't realize that. Thank you!

bluGill 2y ago

aluminum has terrible metal fatigue issues. Ships that have been perfectly fine for years will suddenly just fall into pieces. Trucks where weight matter do often use aluminum trailers, but they keep careful track so they are scrapped before they fall apart. This fall about is not something an inspection will catch (not 100% true, ultrasound and other inspection methods will catch some of this, but for discussion it is close enough to say you just scrap aluminum before it fails instead of inspecting) That isn't to say aluminum can't be used for ships. Only that it is tricky.

jillesvangurp 2y ago
There are different alloys of aluminum with different properties. Just like steel. And of course it's been used in the aviation industry for a long time as well. Car manufacturers are using aluminum castings in cars these days. And there are engine blocks made out of aluminum as well. Anyway, this is the ship yard I mentioned. They have a few decades experience making ships out of aluminum: https://en.wikipedia.org/wiki/Incat https://en.wikipedia.org/wiki/Incat
- AceyMan 2y ago
  As I understand it, the gotcha with aluminum is: there is no such thing as non-fatiguing stress — whereas, say, steels, have a range of elasticity where it can operate and not lose strength (or get cold-work hardened). With aluminum, any flexion — no matter how little — marginally reduces the strength of the material. Ergo, even under ideal conditions it's saddled with a limited service life.
  - HPsquared 2y ago
    You just design it so the stress in the material gives a very long fatigue life (as in, how many zeros do you want?). It doesn't have a defined "fatigue limit", but it may as well have.

LgWoodenBadger 2y ago

I don't understand how an aluminum structure can withstand the stresses in bulk-oriented ships without fatiguing to destruction in the first rough weather.

HPsquared 2y ago
You make it thick enough so the material isn't stressed. This does require rigorous engineering processes, but it's pretty common.