DARPA’s silent MHD magnetic drives for replacing naval propellers(naval-technology.com)
naval-technology.com
DARPA’s silent MHD magnetic drives for replacing naval propellers
https://www.naval-technology.com/features/darpa-silent-mhd-magnetic-drives-for-replacing-naval-propellers/
108 comments
MHD is nothing new though, so if it has not yet replaced propellers I'm guessing it is because of practical issues like corrosion, electrolysis and so on alluded to in the article that DARPA seems to have found solutions for but which are not going to be available for the general public for obvious reasons.
Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generator or the added weight and cost of a battery system.
Also it's all electric so it poses the usual problems like the added complexity of an on-board electric generator or the added weight and cost of a battery system.
> because of practical issues
Like fitting supercooled tesla-power magnets to a moving vehicle, perhaps.
> the added complexity of an on-board electric generator
But you don't need that if the vessel is electric-powered, like a nuclear-powered sub; and I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion (i.e. an electric ship powered by a fossil-fuel generator).
Like fitting supercooled tesla-power magnets to a moving vehicle, perhaps.
> the added complexity of an on-board electric generator
But you don't need that if the vessel is electric-powered, like a nuclear-powered sub; and I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion (i.e. an electric ship powered by a fossil-fuel generator).
> But you don't need that if the vessel is electric-powered, like a nuclear-powered sub
Yep.
> I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion
Sure, like a diesel-electric locomotive.
It turns out in some situations it's better to eat the conversion loss from electric generation rather than using a direct mechanical linkage, because then you can use flexible cables and electrical control systems rather than a bunch of mechanical folderol
Yep.
> I believe some modern warships use a traditional motor to drive a generator, which drives an electric motor for propulsion
Sure, like a diesel-electric locomotive.
It turns out in some situations it's better to eat the conversion loss from electric generation rather than using a direct mechanical linkage, because then you can use flexible cables and electrical control systems rather than a bunch of mechanical folderol
Per the article the previous generation was only roughly 30% efficient, which makes it just not competitive with propellers.
Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.
Swapping out your diesel motor with rotating shafts going through your hull and an alternator to generate electricity for a diesel generator that just generates electricity is reducing complexity, not adding it.
the alternator is already there, too, since modern diesel submarines are actually diesel-electric submarines, able to charge batteries with the diesel engine and then shut it off and run from the batteries to go quiet
so, the difference is between props vs. no props, which is big.
so, the difference is between props vs. no props, which is big.
In context I'm arguing for use on commercial surface boats and ships.
But they too have alternators (and/or dedicated generators)... because it turns out electricity is really useful.
But they too have alternators (and/or dedicated generators)... because it turns out electricity is really useful.
So, the USN actually did park that Soviet sub captained by James Bond in a creek somewhere. I knew it!
I agree that an innovation of this magnitude would have a huge impact on naval propulsion if it were publicly available though I’d imagine the tech would be locked down to a ridiculous level. It’s likely destined to only appear in nuclear submarines.
Yeah, no. Once it's known that it's possible to achieve, some enterprising company will quickly replicate it.
Unless, of course, it needs unobtainable levels of power.
Unless, of course, it needs unobtainable levels of power.
Well, people are talking about 90% efficiency up-thread. You can't need unobtainable levels of power and still have 90% efficiency, as people move boats around every day.
Also, about the need for a coolant, well, the fixed costs for it are on the order of a few $100/m on most cities nowadays. If people start to use lots of it, the fixed costs will fall to zero. (The variable cost isn't high, but it also doesn't dictate the boat size.)
Also, about the need for a coolant, well, the fixed costs for it are on the order of a few $100/m on most cities nowadays. If people start to use lots of it, the fixed costs will fall to zero. (The variable cost isn't high, but it also doesn't dictate the boat size.)
You can absolutely have an energy requirement cliff that has to be exceeded for a thing to work before you can even measure it's efficiency. Trying to push something from standstill vs. keeping it moving.
Yes, there exist stuff that behaves like this.
MHD isn't one.
MHD isn't one.
If it needs unobtainable levels of power, that means it's not efficient. If it's efficient you can use a diesel generator in place of your diesel engine and obtain the same amount of power.
Not quite. It might be efficient, but only if you need megawatt-level propulsion power.
This is not uncommon in engineering in general. There are many, many examples of devices that are highly efficient but only at higher power levels/speeds.
This is not uncommon in engineering in general. There are many, many examples of devices that are highly efficient but only at higher power levels/speeds.
The government can and does lock down intellectual property for national security reasons.
The US government effectively locked down Juliet Marine Systems' IP, and gave the inventor no compensation for doing so. Took about more than 5 years for the inventor get any relief.
https://www.boatblurb.com/post/the-us-military-ghost-ship-is...
The US government effectively locked down Juliet Marine Systems' IP, and gave the inventor no compensation for doing so. Took about more than 5 years for the inventor get any relief.
https://www.boatblurb.com/post/the-us-military-ghost-ship-is...
The US government won't be able to lock down a company in Sweden or Turkey. It's not like the principles of MHD propulsion are in any way secret. It's just that we now have much better superconducting magnets.
There's no reason to assume that. A ton of things DARPA pathfinds are commercialized, including the globe spanning network we're using to converse atm.
I'm not sure it would be restricted so much as just way too expensive to be practical. There is also the practical considerations of generating 20T magnetic fields out in the real world and around people.
Yeah, that seems to be the way it always goes. It's not actually all that difficult to build an AESA radar in your garage, it's just very hard to get enough of the types of parts needed for a useful one without nation state level funding. The FPGAs they use are on Digikey....for 5-10k ea.
Or on the vessel itself it would have to be shielded for the people and for any equipment.
I've seen experiments where a device using a paddle was put against a person's head and a strong magnetic field emitted. It was a TV reporter for Discovery Channel Canada and her jaw convulsed, she did not look pleased.
I think the experiment was about spirituality of all things. How to induce a feeling of a presence to a person. I believe it was called the God helmet but in the video I saw it was a paddle.
I've seen experiments where a device using a paddle was put against a person's head and a strong magnetic field emitted. It was a TV reporter for Discovery Channel Canada and her jaw convulsed, she did not look pleased.
I think the experiment was about spirituality of all things. How to induce a feeling of a presence to a person. I believe it was called the God helmet but in the video I saw it was a paddle.
"Trans-cranial magnetic stimulation" — it has both been called "the god helmet" and has been used in that way.
IIRC it's a pulsed field to induce electric fields in your brain, and also has an extremely short range.
Somewhat more significant to human health is that magnetic material can be rapidly drawn towards the magnets, with the force on a steel office chair can exceed its own structural capacity in standard medical magnetic equipment: https://youtu.be/6BBx8BwLhqg
At very high field strengths, you also need to account for "your blood is electrically conductive, and electrical conductors resist motion when in a magnetic field due to induced electrical currents". According to test subjects, this "tingles".
At the most extreme fields strengths we can currently make, you also have to account for the water in your body being diamagnetic and repelling the magnets, but we can't ask any of the test subjects what that feels like as they were a frog and a rat because that's all that would fit in the tube.
IIRC it's a pulsed field to induce electric fields in your brain, and also has an extremely short range.
Somewhat more significant to human health is that magnetic material can be rapidly drawn towards the magnets, with the force on a steel office chair can exceed its own structural capacity in standard medical magnetic equipment: https://youtu.be/6BBx8BwLhqg
At very high field strengths, you also need to account for "your blood is electrically conductive, and electrical conductors resist motion when in a magnetic field due to induced electrical currents". According to test subjects, this "tingles".
At the most extreme fields strengths we can currently make, you also have to account for the water in your body being diamagnetic and repelling the magnets, but we can't ask any of the test subjects what that feels like as they were a frog and a rat because that's all that would fit in the tube.
The majority of DARPA research is public and you can get copies of the software or specs via an email typically.
I suspect the Navy actually does have room temperature superconductors[1] ... which could make this a practical technology.
[1] https://patents.google.com/patent/US20190058105A1/en
[1] https://patents.google.com/patent/US20190058105A1/en
Google scholar shows that that patent 'author' has three patents
1. Piezoelectricity-induced High Temperature Superconductor
2. Craft using an inertial mass reduction device
3. High frequency gravitational wave generator
https://patents.google.com/?inventor=Salvatore+Cezar+Pais
And I think with those three "inventions" one could construct a space-ship that could travel to Alpha Centauri at a meaningful fraction of 'c'.
Extraordinary claims require extraordinary evidence. Whatever is going on here, it's hard to take this document as evidence for a working room temperature superconductor...
https://patents.google.com/?inventor=Salvatore+Cezar+Pais
And I think with those three "inventions" one could construct a space-ship that could travel to Alpha Centauri at a meaningful fraction of 'c'.
Extraordinary claims require extraordinary evidence. Whatever is going on here, it's hard to take this document as evidence for a working room temperature superconductor...
>Extraordinary claims require extraordinary evidence
The granting of a United States patent should be sufficient evidence to at least consider it possible that such things have been achieved.
The granting of a United States patent should be sufficient evidence to at least consider it possible that such things have been achieved.
I'm taking that 90% efficiency figure with a grain of salt since that is the paper calculation in a technology that is still very experimental.
Isn't this the plot for Hunt for Red October?
Yes! I was thinking that as I read it. Alec Baldwin even says magneto hydrodynamic drive.
Yet another example of Tom Clancy’s incredible knowledge of the intricacies of what the military had on their radar and working that into great stories.
Yet another example of Tom Clancy’s incredible knowledge of the intricacies of what the military had on their radar and working that into great stories.
Magneto Hydrodynamic Drives have been a publicly researched concept since the 60s. Magnetic pumps are used routinely in industry. You're definitely exaggerating how visionary Clancy was.
I'm not talking about him coming up with the ideas. But him weaving it as a thing the US Navy had been concerned about the Soviets building – I am saying it's very likely that the US Navy's concern about these drives being used in subs wasn't made up, and maybe some related conversations he had with contacts/sources, that turned out to be one of many seeds that made for a compelling story.
He did write about using an airliner as a missile years before it happened.
I recently re-read The Hunt For Red October, and what struck me was that there actually wasn't and mention of Magneto-hydrodynamic drive. As I recalled, the book describes a series of propellers in a duct. Certainly interesting for isolating sound, but it struck me as much more simplistic from the superconducting systems described in the movie.
No shade intended towards Mr. Clancy however. I got the impression that he was quite lauded for not simply describing tech (which other thriller writers did as well) but getting into the nuts and bolts of how they operated. That was what really set him apart.
No shade intended towards Mr. Clancy however. I got the impression that he was quite lauded for not simply describing tech (which other thriller writers did as well) but getting into the nuts and bolts of how they operated. That was what really set him apart.
Here's one discussion in the book, clearly describing impellers in a tunnel. https://archive.org/details/huntforredoctobe0000clan_l6h7/pa...
For example, it says the US "looked at this back in the early sixties and got to the model stage before dropping it. One of the things they discovered is that one impeller doesn’t work as well as several. Some sort of back pressure thing."
Wikipedia says, at https://en.wikipedia.org/wiki/The_Hunt_for_Red_October :
> The movie is a nearly faithful depiction of the novel even though there are many deviations, including Red October traveling up the Penobscot River in Maine to dry dock, the omission of the Royal Navy task force including Ryan's time aboard HMS Invincible, and the "caterpillar drive" being described as a magnetohydrodynamic drive system, essentially, "a jet engine for the water", rather than a drive powered by a series of mechanical impellers inside flow tunnels.
For example, it says the US "looked at this back in the early sixties and got to the model stage before dropping it. One of the things they discovered is that one impeller doesn’t work as well as several. Some sort of back pressure thing."
Wikipedia says, at https://en.wikipedia.org/wiki/The_Hunt_for_Red_October :
> The movie is a nearly faithful depiction of the novel even though there are many deviations, including Red October traveling up the Penobscot River in Maine to dry dock, the omission of the Royal Navy task force including Ryan's time aboard HMS Invincible, and the "caterpillar drive" being described as a magnetohydrodynamic drive system, essentially, "a jet engine for the water", rather than a drive powered by a series of mechanical impellers inside flow tunnels.
It was published by the (US) Naval Institute Press, their first published work of fiction. [0]
And yes. https://m.youtube.com/watch?v=SMCoIwsaRVw&t=1m31s
[0] https://en.m.wikipedia.org/wiki/The_Hunt_for_Red_October#Com... https://en.m.wikipedia.org/wiki/United_States_Naval_Institut...
And yes. https://m.youtube.com/watch?v=SMCoIwsaRVw&t=1m31s
[0] https://en.m.wikipedia.org/wiki/The_Hunt_for_Red_October#Com... https://en.m.wikipedia.org/wiki/United_States_Naval_Institut...
Yes. "Caterpillar drive". Fantastic book and movie.
I have watched the movie dozens of times. I really need to read the book.
The book's better, if you liked the movie.
It was actually the first "adult" book I read. Maybe when I was 9? I told my father I was bored of school books, and he handed it to me.
As well as Clancy's other stuff!
Just stop reading at 2000 (last recommended book: The Bear and the Dragon). After that he started phoning it in / lending out the name as ghostwritten brand.
It was actually the first "adult" book I read. Maybe when I was 9? I told my father I was bored of school books, and he handed it to me.
As well as Clancy's other stuff!
Just stop reading at 2000 (last recommended book: The Bear and the Dragon). After that he started phoning it in / lending out the name as ghostwritten brand.
I remember sitting in the dining room at four AM. JUST ONE MORE PAGE.
Beat me to it. Happens to be my favorite movie, ever. I’ve watched it so many times and I’m still not sick of it. What’s so beautiful about it is that it’s pure storytelling without a preachy agenda, though the irony is that it’s very much about politics and patriotism.
The book is even better. I watched the movie about a half dozen times before I read the book and was amazed that I liked the book more. And I still think the movie is great.
It’s one of the very few cases where I think both are great even though different and I don’t really see a way to improve either.
"The thing about a new propulsion system, Captain, is its silence... and you don't have to touch a thing. It's all moved by electric currents and magnetic fields. Just one more step towards making submarines even more silent. The next 'Red October', if you will."
"Can you ping, Washily? One ping only, pleashe."
“If we meet the right shot, this will work. If we get some… buckaroo?…”
He needed someone on the US side to figure out he was defecting and meet him with a plan to help. He gave it 1 chance in 3. Loved that moment you reference when he realizes he did indeed meet the right shot.
He needed someone on the US side to figure out he was defecting and meet him with a plan to help. He gave it 1 chance in 3. Loved that moment you reference when he realizes he did indeed meet the right shot.
The Vilnius Schoolmaster deserves to be quoted correctly: “Give me a”, not “Can you”
It’s Tom Clancy’s future, we just live in it.
Engage the caterpillar dive, Vasily!
Yamato-1 looks so fast. I saw this ship in Kobe and i felt like in a Science Fiction movie. But ..
> these ships were only able to reach speeds of 15 km/h.
https://en.m.wikipedia.org/wiki/Yamato_1
> these ships were only able to reach speeds of 15 km/h.
https://en.m.wikipedia.org/wiki/Yamato_1
The 70,000 ton Yamato battleship could go 50 km/h circa 1940:
https://en.m.wikipedia.org/wiki/Yamato-class_battleship
https://en.m.wikipedia.org/wiki/Yamato-class_battleship
Not to speak of its later wave-motion engine: https://yamato.fandom.com/wiki/Wave-motion_Engine_(2199)
This is probably classified, but just how sensitive are MAD systems? A football field ship is a big chunk of metal and we’re ankle to detect them at some depth. One that has a 20 tesla magnet seems like painting a target on your own aft.
Wikipedia has some numbers - obviously there could be a difference between them and reality but they are a plausible starting point.
https://en.wikipedia.org/wiki/Magnetic_anomaly_detector#Oper...
https://en.wikipedia.org/wiki/Magnetic_anomaly_detector#Oper...
I remember this technology being a plot point in a Clive Cussler novel, and then being standard issue on new boats in most Cussler novels after that. I see Tom Clancy also featured it in his books even earlier. It’s always cool when you first learn about some tech from near-future action novels and then later that tech becomes real; feels very futuristic.
By using AC you can induce current in the water and avoid the need for electrodes, but low efficiency. By using high strength permanent magnets they can trade those.
I wonder if it sounds like whales humping or a seismic anomaly…
You’ll just have to speed up the recording to 10x to find out… :)
It was Paganini
Well, it's claimed to be silent, so probably not.
But, I went straight to whales as well, this could be a great option for a quiet whale watching boat.
But, I went straight to whales as well, this could be a great option for a quiet whale watching boat.
(These are Red October references)
From the whales' point of view, if it is silent it would be great if every boat had it.
1. https://www.nhm.ac.uk/discover/news/2022/july/underwater-noi...
2. https://www.theguardian.com/environment/2022/apr/12/ocean-of...
3. Woods Hole, 2005: https://www.whoi.edu/oceanus/feature/how-to-see-what-whales-...
1. https://www.nhm.ac.uk/discover/news/2022/july/underwater-noi...
2. https://www.theguardian.com/environment/2022/apr/12/ocean-of...
3. Woods Hole, 2005: https://www.whoi.edu/oceanus/feature/how-to-see-what-whales-...
Ask Jonesie
> If power and efficiency issues are resolved,
My gut feel is that this is a pretty grossly inefficient system by nature. Inducing current in seawater just to give magnetic traction something to push off against seems semi absurd.
My gut feel is that this is a pretty grossly inefficient system by nature. Inducing current in seawater just to give magnetic traction something to push off against seems semi absurd.
I mean rockets are absurd - burn gas to throw it behind you to push off against. Works in space (the NYT regrets the error).
https://www.nytimes.com/2001/11/14/news/150th-anniversary-18...
https://www.nytimes.com/2001/11/14/news/150th-anniversary-18...
That's very true, but "efficient" isn't usually an adjective thrown at a rocket.
Uhhh I feel like rocket makers are obsessed with efficiency. A modest half a percent makes a huge difference in fuel fraction & lift capabilities.
Rockets may be broadly inefficient but they are as efficient as we can make them.
Rockets may be broadly inefficient but they are as efficient as we can make them.
I understand. They're the only orbital game in town, and will be until <INSERT_PET_FUTURISTIC_THINGY>. I guess what I'm, saying, it's more that "efficient" isn't a word that pops up in your head when you imagine "rocket". It's like a demure Dodge Hellcat owner, or a contemplative WWE star.
semi absurd is kinda why DARPA exists!
The Register used to make fun of DARPA, saying things like “where every laugh is a mad cackle.”
While we all communicate using TCP/IP, invented as a DARPA program for robust communication in the event of nuclear conflict...
It's an urban legend. ARPANET was an overgrown university network.
And TCP/IP was one of many potential standard protocols
https://en.m.wikipedia.org/wiki/Protocol_Wars
https://en.m.wikipedia.org/wiki/Protocol_Wars
What? VLSI, VHDL, Multics, Hypertext, GaAs semiconductors, autonomous navigation, GPS, and packet switched networking were a few things they funded. Totally absurd, right? For every successful tech, they probably explored scores that didn't pan out. Basic, high risk research has huge payoffs across society even if you don't like who's funding it or why.
Purely-electric devices tend to have this property that if you maximize or minimize something with no clear theoretical limitation, your efficiency grows all the way to 1.
On the case of this, my gut feeling tells me that making the magnet really, really big will do it.
On the case of this, my gut feeling tells me that making the magnet really, really big will do it.
Passing electric current through seawater... Electrolysis will occur, producing hydrogen and chlorine gas (and some oxygen too).
It's not all positive, the are some negatives to this technology as well!
It's not all positive, the are some negatives to this technology as well!
A couple of years ago someone built a model submarine with an actual MagnetoHydroDynamic drive:
“Magnet Powered Submarine - The Hunt for Red October IRL!” https://www.youtube.com/watch?v=nFsiydplCtw
The corresponding blog entry includes the STL files for 3D-printing the submarine’s hull:
https://www.kjmagnetics.com/blog.asp?p=red-october
“Magnet Powered Submarine - The Hunt for Red October IRL!” https://www.youtube.com/watch?v=nFsiydplCtw
The corresponding blog entry includes the STL files for 3D-printing the submarine’s hull:
https://www.kjmagnetics.com/blog.asp?p=red-october
> The MHD drive does not have moving parts, reducing noise and vibration, making it harder to detect via sonar
Uh what? Sonar is active detection, using the bouncing of emitted sound waves, no? Then I don't see how a silent engine makes it harder to detect via sonar if the signals will still bounce just as hard from the hull.
Uh what? Sonar is active detection, using the bouncing of emitted sound waves, no? Then I don't see how a silent engine makes it harder to detect via sonar if the signals will still bounce just as hard from the hull.
There is passive sonar too, which is just listening.
Relevant to this: unimaginably vast amounts of effort have gone into making propellers a little bit quieter so they are harder to hear while still allowing reasonably high speeds. A lot of that is to do with avoiding cavitation at the prop tip, which is a) noisy, and b) very destructive. no prop, no prop noise...
A submarine is like a ninja. It tries to sneak around undetected.
Using active sonar is like placing a siren on your head.
Using active sonar is like placing a siren on your head.
What you are describing is active sonar. The downside of active sonar is that it also clearly reveals your own position.
As such, modern submarine warfare relies mostly on passive sonar - very sensitive microphone arrays (sometimes towed behind) to listen for audio signatures of surface and subsurface ships.
This means that submarine navies (and anti-submarine surface fleets to some degree) put a high priority on the ability to run quietly. A lot of work is put into things like propellor design to minimise the noise but there's a limit to how far you can go to eliminate cavitation and other noise sources. MHD, which would just be water flowing through a pipe, can potentially be much quieter.
As such, modern submarine warfare relies mostly on passive sonar - very sensitive microphone arrays (sometimes towed behind) to listen for audio signatures of surface and subsurface ships.
This means that submarine navies (and anti-submarine surface fleets to some degree) put a high priority on the ability to run quietly. A lot of work is put into things like propellor design to minimise the noise but there's a limit to how far you can go to eliminate cavitation and other noise sources. MHD, which would just be water flowing through a pipe, can potentially be much quieter.
The idea of a boat with no moving parts is weird.
Since we’re already this deep into science-fiction, could we superheat air and then run the plasma through this in order to create a land or air vehicle with no moving parts?
Since we’re already this deep into science-fiction, could we superheat air and then run the plasma through this in order to create a land or air vehicle with no moving parts?
It's been done, without superheating anything https://news.mit.edu/2018/first-ionic-wind-plane-no-moving-p...
The interesting question is could you do it efficiently and with sufficient thrust - I don't know.
The interesting question is could you do it efficiently and with sufficient thrust - I don't know.
I doubt this would be practical taking into account how strong magnetic field has to be.. I am wondering... am I missing something or nobody seriously thought about it?
Can something like this work for airships? Ionize and push air with all the solar electricity their surface area could generate?
Wouldn't the intense electro-magnetic signature of this drive make it highly detectable in an otherwise quiet ocean?
Bay area waters were (are?) used as a naval magnetic silencing range. Most navy ships have degaussing coils that calibrate with magnetosphere
https://www.dropbox.com/s/qansmciigewti4n/IMG_2957.JPG?dl=0
https://www.dropbox.com/s/qansmciigewti4n/IMG_2957.JPG?dl=0
Degaussing in a bay is much different from trying to cancel out 20T(!!!) of EM signature
You don’t need to cancel it. Most electromagnetic surveillance systems have detection thresholds (e.g. in radar you have distance gate and return signal filters). Same applies for magnetically activated mines. Reducing the signature below detection thresholds is often enough. Alternatively masking the signature with another signal to confuse the detector also often works well.
EDIT: on second thought, if you can build a device to generate 20T you can probably build a contraption to cancel it out as well. It would most likely boil down to the economics or the scale of the contraption required.
EDIT: on second thought, if you can build a device to generate 20T you can probably build a contraption to cancel it out as well. It would most likely boil down to the economics or the scale of the contraption required.
Very cool, and although the submarine may be silent, the magnetic anomaly could theoretically be detected and tracked.
It won’t be completely silent because you’re still jetting a lot of water out the back of the submarine.
"Captain, they've escaped."
"How?"
"Drove into freshwater"
[deleted]
are these power hungry?
wondering if it could replace the propeller on self-propelled hydrofoil surfboards
wondering if it could replace the propeller on self-propelled hydrofoil surfboards
The world trembled at the sound of our rockets. Now they will tremble again at the sound of our silence.
If it's just some REBCO super-conducting magnets and conductive surfaces it might be reasonably inexpensive too. And without moving parts it could be a maintenance win as well.
I'm no sailor, but at first glance this seems like it would potentially replace all propulsion on boats/ships big enough to justify cooling REBCO. Obviously conditioned on actually reaching that fairly outrageous target.
[1] https://www.britannica.com/technology/naval-architecture/Act...