As nuclear is already used on aircraft carriers, and with a major cargo ship not having a large crew including guests so it can be properly scrutinized and managed by engineers, why hasn’t this technology ever carried over for commercial operators?
Similarly for hydrogen, why (or are?) ship builders not trying to build hydrogen powered engines? Seeing the massive size of engines (and fuel) they have, could they make super-sized fuel cells and on-board synthesizing to no longer be reliant on gas?
In: Engineering
Would it not also be a safety issue as cargo ships aren’t that well manned and would need to protect themselves against pirates and others who’d use a nuclear reactor for terroristic gains etc?
Because their expensive and cargo ships don’t need the ability to stay out at sea for potentially years at a time. They have to dock to unload cargo pretty regularly and can top up on fuel when doing so.
Nuclear: We tried, but a combination of costs and ports reluctant to receive them meant the idea did not catch on.
[https://en.wikipedia.org/wiki/NS_Savannah](https://en.wikipedia.org/wiki/NS_Savannah)
[https://en.wikipedia.org/wiki/RV_Mirai](https://en.wikipedia.org/wiki/RV_Mirai)
On Hydrogen, it is simply cost. Ships (excl some areas with restrictions near ports) burn the cheapest, nastiest fuel they can find. Hydrogen (Mostly it is made via steam reformation of natural gas, so is fossil fuel derived anyway) simply costs a lot more than this. Unless it is mandated, or massively subsidized, ship owners aren’t going to bother. Also you would have to do cryogenic storage to hold enough of it. Not a deal breaker, but it is technically challenging.
Lots of answers on nuclear, so I’ll reply on the hydrogen-power part, especially since it pertains to my job.
Hydrogen is alot less convenient compared to the fuel oil that is being used to power our cargo ships now.
Hydrogen is:
Extremely flammable, toxic and colorless, so more dangerous when there is a leak
A gas at ambient temperature, so more difficult and expensive to store onboard
Has way lower energy density, so you need alot more of it to travel the same distance, so higher cost as well. This also means you need to make more frequent stops, or dedicate more of your storage space to storing hydrogen instead of your money-making cargoes
It doesn’t make sense to produce hydrogen on board for immediate use (instead of storing hydrogen to consume it) because you need way to much space to generate or store sufficient electricity to produce hydrogen at a fast enough rate to power your fuel cells.
However, the world is increasingly moving away from fuel oil and towards green hydrogen. green hydrogen carriers and green methanol in order to combat climate change.
The insurance rates of a nuclear powered cargo ships must be insane. The potential liability of an accident with such a ship is not something a shipping company can survive. There are few insurers that can survive it. I suspect there’s prosperous countries that wouldn’t survive it.
I would imagine any ship carrying nuclear material would have to have all kinds of extra security onboard and probably extra ships to accompany it, which would add to the already high cost.
There are a few reasons, so let’s attack nuclear and hydrogen separately.
*Nuclear*
There are a few cost aspects here. Reactors are expensive yes, but they also front-load the expense. With a normal ship, the bulk of the cost is spread over the lifetime as fuel cost. With nuclear, you front load it, making ships more expensive to buy. This is less appealing to ship owners for obvious reasons.
Our current infrastructure is designed around diesel powered ship. This makes it more expensive to keep a nuclear ship seaworthy, but is a cost that could come down with more adoption.
You also have piracy, safety, etc. concerns, but I’m going to ignore them.
*Hydrogen*
The big issue is energy density. Hydrogen just doesn’t give you anywhere near as much energy in the same space as diesel. When you have to carry all of your fuel, this is very important.
You mentioned making your own hydrogen onboard – really that’s not that feasible for a host of reasons, largely due to amount of power needed (big ships require several MW in port, and that is without propulsion).
In the case of nuclear, the security concerns are too great. What harbour is going to allow a potential dirty bomb floating in on a regular basis? Even if not a deliberate act, have a look at how many accidents happen between ships and then ramp up the severity of everything was nuclear. Then you have the economic…. What shipping company is going to want to pay for the training, certification, regular inspections and salary of having a crew nuclear rated? Finally, what shipping company is going to want to pay to dispose of a nuclear powered ship? What insurance company is going to insure a fleet of nuclear powered ships, knowing the cost of salvage? Hopefully you’re starting to see some of the issues…
As for hydrogen, the simple reality is that hydrogen is not economic, not is it ever likely to be. The cheapest way to make it is through steam reforming of methane, a process that is more carbon intensive than just burning the natural gas directly. Even then the cost is ~5x that of diesel. If you were to use renewably derived hydrogen, the cost would easily be ~10x. Then when you consider that most cargo vessels don’t even shell out for diesel, preferring to burn the much cheaper bunker fuel (effectively tar, a waste product of refining so thick that they need to heat it just to make it flow), hydrogen would be astronomically more expensive making the shipper unviable in the market.
In the real world, neither of these are viable options. The only people who think they are, are the folks who have adopted each respective technology. They then put the cart before the horse by confusing the fact that just because something may be technically possible, that thing then must be the solution.
If you want to know how we’re going to decarbonize shipping, start with the economics and work backwards. The cheapest way to power something that’s not polluting is always going to be to directly electrify it. Container ships are already set up to load and unload shipping containers. The infrastructure to handle a few loaded with batteries that get swapped at every port. Lo, what’s this? It’s already starting to happen in the massive amount of river shipping over in China and in the cruse market over in Europe? Neat. But that won’t get a ship across the ocean you say. True. But considering that a substantial portion of maritime shipping is literally hauling fossil fuels around, a good chunk of that shipping is going away anyway. The remainder will likely be replaced by biofuels. A carbon neutral diesel analogue that’s a drop in replacement for what we do now.
Yes, it’s not as cheap as digging up diesel today, but as soon as the world puts a price on carbon it will be. There’s also not going to be any shortage of the stuff considering how much organic waste we’re generating already that could be put to much better use than just off gassing methane into the atmosphere.
So you’ve gotten lots of answers about the nuclear side of your question. And I’d agree with the general theme.
Too expensive to build and operate. And lots of countries would not allow a civilian nuclear ship to dock limiting its usefulness.
For hydrogen the answer is interesting. Modern marine diesel engines can burn almost any compressed gas quite easily at engine loads exceeding 20%.
The issue is not an engine that can use it but how to store the gas on a ship. Liquid fuels like diesel and heavy fuel oil are easy they aren’t under pressure and we can store them in weirdly shaped tanks that make up part of the ship. And compressed gas needs a cylindrical tank and storing flammable gasses at the bottom of a ship is bad news.
Feel free to ask me any further questions here. I’ve been building and maintaining marine diesel engines for almost 20 years now and have done many installations.
As far as Nuclear goes, I don’t think that people have touched on the real reason the military uses it – they don’t have to go into port to refuel for very long times (many years at a time). Carriers and combat ships can stay on mission for extended periods of time, submarines can hunker down for many years (really only need to come up for more food eventually), etc. If something happens and the ships cannot physically come into port, they will be ok.
Don’t need to do this with cargo ships. Diesel is cheap enough and frankly the cost of it get priced into the cost of doing business, so the ship operators don’t care too much (within reason) about the price of fuel because they are going to pass that on to the customers. Nuclear requires a lot of investment and technical staff that isn’t worth the additional money.
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