Launch HN: Maritime Fusion (YC W25) – Fusion Reactors for Ships
95 comments
·February 26, 2025uranium
"Downtime for maintenance is part of normal operations, making this a far more forgiving early application of fusion, unlike the grid where every down hour is lost revenue."
Planned maintenance, sure, but unplanned maintenance means the same lost revenue, plus you're stuck floating in the middle of the pacific ocean, possibly in need of parts or debugging expertise that only exists half a planet away or, for that matter, food. It's certainly a good idea to find a niche to make market entry easier, but I would guess that reliability requirements are actually higher for ships than for microgrids. Find some isolated town or island running off flaky diesel generators on shipped-in fuel and negotiate a reasonable SLA.
This ignores, of course, the bigger problem: making fusion work at all at Q > 1. If it were me, I'd work on solving that before worrying too much about optimizing market entry. So far every single fusion effort has failed to clear that hurdle, and any effort on the other parts is wasted if you can't actually make power.
jimbru
The first ocean-going steamships still had sails - it took many years for steam power to fully displace sail. Presumably a new maritime power system, like fusion, would follow a similar pattern.
https://en.wikipedia.org/wiki/Steamboat#Sea-_and_Ocean-going
simpaticoder
There is something very compelling about a fusion-powered ship also having sails.
phtrivier
> and we believe we’ll witness Q > 1 within a few (say 3) years. That’s huge.
I think it fits squarely in the "requires extraordinary evidence" bucket - what makes you so bold ?
Also, what's you intermediate plans between :
2025 -> Post on HN
2028 -> Q>1 achieved (by you ? by someone else ?)
???? -> ????
20xx -> a ship goes to sea powered by a fusion reactor
???? -> ????
2060 -> fusion is so easy, let's use it for baseload
Sorry if I sound stark, but I'm already burnt out and fed up with the "breakthroughs" on batteries that never materialize - I have a very low tolerance threshold for startups promising fusion for next week ;)
If you're on to something, more power to you - we need that yesterday.
dust42
Also, what's you intermediate plans between :
2025 -> Post on HN
2028 -> Q>1 achieved (by you ? by someone else ?)
CFS plans Q>1 for 2027 with a tokamak design. If they succeed then there will be plenty of VC for similar designs. I'd place my bets that CFS succeeds with Q>1. And I think the real problem will be the energy flux and neutron handling and thus much more a material sciences problem than a plasma physics problem. Thus the idea to look for a niche that has lower power needs is a very clever one. My bet would be rather on Maritime Fusion than Helion. But nevertheless, CFS will be likely first at Q>1 however there is always space for another competitor.
beambot
Let's also be really explicit... CFS is targeting Q>1 by 2027 for nuclear fusion via the SPARC reactor, but not Q>1 for electrical generation. The latter is slated for sometime in the early 2030s via the subsequent ARC reactor.
All of this is driven by HTS. Fusion reactors (generically) scale to the inverse^4 of magnetic field strength. HTS doubled the achievable magnetic field strength of electromagnets, which means that ITER-like performance can be achieved in university-scale reactors at comercially-viable, lower costs.
Dr. Dennis Whyte (MIT Nuclear Eng Prof) gave a great seminar at Berkeley that covered some technical nuances. It's mandatory watching if you want to geek out and understand the fusion hype: https://www.youtube.com/watch?v=rY6U4wB-oYM
ClumsyPilot
> that ITER-like performance can be achieved in university-scale reactors at comercially-viable, lower costs
Are they going to upgrade it or it’s already obsolete before it was even finished?
jtcohen
Exactly this !!
isatty
The HN battery checklist needs to be reworked for fusion power. Arguably, even though people think it’s trolling to use the checklist, I’ve found it surprisingly educational each time.
quchen
Sounds interesting, could you post that checklist?
d_silin
This one I presume:
----------------------------------------------------------------
Dear battery technology claimant,
Thank you for your submission of proposed new revolutionary battery technology. Your new technology claims to be superior to existing lithium-ion technology and is just around the corner from taking over the world. Unfortunately your technology will likely fail, because:
[ ] it is impractical to manufacture at scale.
[ ] it will be too expensive for users.
[ ] it suffers from too few recharge cycles.
[ ] it is incapable of delivering current at sufficient levels.
[ ] it lacks thermal stability at low or high temperatures.
[ ] it lacks the energy density to make it sufficiently portable.
[ ] it has too short of a lifetime.
[ ] its charge rate is too slow.
[ ] its materials are too toxic.
[ ] it is too likely to catch fire or explode.
[ ] it is too minimal of a step forward for anybody to care.
[ ] this was already done 20 years ago and didn't work then.
[ ] by this time it ships li-ion advances will match it.
[ ] your claims are lies
d_silin
And one for fusion
----------------------------------
Dear Nuclear Fusion Power Claimant
Thank you for your submission of proposed new revolutionary nuclear fusion power technology. Your new technology claims to solve humanity's energy problems, produce unlimited clean energy, and is just months away from commercialization. Unfortunately, your technology will likely fail, because:
[ ] it requires materials that cannot be produced at any scale.
[ ] its energy gain (Q factor) is still substantially less than 1.
[ ] its plasma instabilities modes are completely unknown.
[ ] its plasma modeling behavior relies exclusively on numerical simulations.
[ ] it cannot sustain required plasma confinement criteria
[ ] it cannot handle the neutron flux without rapid degradation of components.
[ ] it requires magnetic fields stronger than currently achievable
[ ] it consumes more energy in cooling systems than it produces.
[ ] your claimed breakthrough violates fundamental physics.
[ ] the same approach was tried in the 1960s, 1970s, 1980s, 1990s and abandoned each time for good reason
[ ] by the time it ships, renewable energy plus storage will be far cheaper.
[ ] your timeline has been "5 years away" for the past 50 years.
[ ] your claims are lies.
Sincerely, The Energy Research Community
tim333
Re Q>1, isn't that just the reaction making more power as heat than you put in and you need something like Q>5 to use the heat to make steam to make electricity to run the thing? (as in wikipedia https://en.wikipedia.org/wiki/Fusion_energy_gain_factor)
ninetyninenine
How about first getting fusion to work for reality before getting it working for maritime.
echoangle
How much design on an actual reactor can you do already if the whole technology isn't even demonstrated yet? How many changes are you prepared to do based on the results of the current scientific reactors?
jtcohen
We can get pretty far along! From magnetic system design, vacuum vessel, RF heating system, cryogenic system, tritium fueling, etc we can start making a ton of progress today. The main things we still need to learn that can influence the design is advanced divertor scenarios and what are best material choices for plasma facing components (PFC's).
echoangle
How certain is it that a tokamak is even able to be run in a stable manner? What if it turns out that a stellarator would be better? Or is that already validated by now?
lukan
The stellarator design makes more sense to me as well and speaking of it, those guys will build a stellarator on land:
https://www.proximafusion.com/press-news/proxima-fusion-and-...
Problems are still many, though (Paper:)
https://www.sciencedirect.com/science/article/pii/S092037962...
nradov
How do you intend to address the crew training issue? Merchant vessel operators tend to hire low wage seamen with limited technical training, plus a few qualified engineering officers. Marine diesel engines are pretty simple and robust but I would imagine that operating a fusion plant might require more technical training.
gpm
So your approach to fusion is "the same CFS but stay at roughly the size of the SPARC prototype instead of scaling up"?
When you say "Q > 1 within a few (say 3) years" are you talking about your own reactors, or others? For that matter, are you trying to partner with CFS and license their technology or are you intending on starting "from scratch" (from whatever is publicly available)?
If that timeline is for fusion in general, what do you think your timeline looks like? Assuming adequate access to funding how soon can you build a Q>1 reactor? How soon after that can you actually go to market and sell a reactor?
---
On an unrelated note, I'm curious what you think of the current approaches to commercial fusion being attempted. Are Tokamaks the only game in town in your mind? Or do the various other approaches also being tried out right now have a good shot (MIF/Zpinches/etc)? Any particular approaches you think are particularly likely to succeed.
This being ycombinator and a startup I'm obligated to say that I don't ask this question because I think it impacts your commercial viability much, the greatest risks in fusion definitely aren't the competitors. I ask it just because I'm curious what people willing to start a fusion company think of the competitors.
---
Ships make a ton of sense to me as an early market. An 11 figure market (according to my own napkin calculations awhile back) where power is much more expensive than on land. At the same time it's never struck me that the hardest part of building a fusion company is finding a market.
jtcohen
Our device is larger than SPARC (~3m major radius) and less power (100MW fusion), hence the confidence in being able to solve the steady-state (repeated inductive pulses) engineering challenges.
We won’t be the first to Q>1, I’m super excited for SPARC to achieve that and will be prepared with champagne.
We’re targeting early 2030’s for our reactor, we’re going straight for the full thing no sub scale reactor in between (we do have a plan for milestone-ing it out in a meaningful way)
I’ve worked on a few alternative approaches earlier in my career (FRC at Princeton, dense plasma focus at LPP Fusion) … I think all fusion approaches are worth looking at, but I’m placing my chips on the tokamak. If I were to pick a runner up, the stellerator.
jandrese
I think your timeline is at best optimistic. I would personally like to see fixed land based fusion power work before we start trying to build them into moving vessels.
Your claim that the shipping industry is "desperate to decarbonize" also needs a citation. From what I've seen shippers top three concerns are "how to minimize costs", "how to reduce costs", and "how to save money". Can you make this system cheaper to operate than heavy fuel oil? If not it is unlikely to gain traction.
jaronchong
I'm just going to put this here. Someone please make this a reality.
### *"Tokamak Sailor"* (To the tune of "Drunken Sailor")
*(Verse 1)* What shall we do with a tokamak sailor? What shall we do with a tokamak sailor? What shall we do with a tokamak sailor? Early in the mornin'!
*(Chorus)* *Ho, ho! Fire up the plasma!* *Ho, ho! Fire up the plasma!* *Ho, ho! Fire up the plasma!* *Fusion in the mornin'!*
*(Verse 2)* Raise the coils and heat up the torus! Raise the coils and heat up the torus! Raise the coils and heat up the torus! Early in the mornin'!
(Chorus repeats)
*(Verse 3)* Confine the plasma, don't let it scatter! Confine the plasma, don't let it scatter! Confine the plasma, don’t let it scatter! Early in the mornin'!
(Chorus repeats)
*(Verse 4)* Sail with the power of fusion glory! Sail with the power of fusion glory! Sail with the power of fusion glory! Early in the mornin'!
(Final Chorus, extra loud!) *Ho, ho! Fire up the plasma!* *Ho, ho! Fire up the plasma!* *Ho, ho! Fire up the plasma!* *Fusion in the mornin'!*
Now all aboard the reactor ship, lads! Keep that plasma hot, and may the tides be ever in our favor!
jtcohen
Lol - on it
foobarian
Dumb layperson question: my understanding of confined plasma fusion from a while ago was that the energy flux across the enclosing boundary can not be handled by known materials without melting down. Is this still true? Not sure if you can share but would be curious to know what the "bottleneck" material is in your design as far as withstanding high temperatures/other extreme conditions goes.
mpweiher
Cool!
Ships were the first application that came to my mind when I read about the roughly container-sized reactor by Lockheed Skunk Worls...that didn't happen.
Are you guys working together the Commonwealth Fusion Systems? JET-Size and HTS magnets sounds a lot like SPAR/ARC.
ilrwbwrkhv
Hot stuff. Both literally and figuratively. An energy breakthrough is really required to get the world back on track. My thesis is that the longer it takes for us to get on the fusion train the more craziness we will see in the world. Wish you all the best and will follow your journey.
12_throw_away
> An energy breakthrough is really required to get the world back on track
Not really, the energy technologies we've needed have been around for about half a century, with quite reasonable economics (albeit less and less so, as the time pressure increases), especially compared to the alternative. The problems that need to be solved are political and economic, not technical.
DaiPlusPlus
> The problems that need to be solved are political and economic, not technical.
You're saying the technical problems involved in fusion power have already been solved. They haven't.
Hey HN, we’re Justin and Jason, co-founders of Maritime Fusion (https://maritimefusion.com/). We’re working on putting fusion reactors on ships—specifically, large container ships and defence applications. Should be easy!
Yes, we know: fusion has been the energy source of the future…and it always will be. But high-temperature superconductors (HTS) have changed the game for magnetic confinement, and we believe we’ll witness Q > 1 within a few (say 3) years. That’s huge.
(Side note: Q is the ratio of input power divided by output power. Q> 1 means the reactor is producing more power than it consumes, achieving ‘breakeven.’)
However, getting to breakeven is just the first daunting challenge. Making the first-of-a-kind (FOAK) reactors cost-competitive on the grid? That might be even harder than achieving breakeven.
That’s why we’re taking this soon-to-be breakthrough in fusion and applying it to the first market we believe makes sense: ships.
Instead of targeting 24/7 baseload grid electricity—where fusion has to compete with solar, wind, batteries, and natural gas—we’re focusing on large commercial shipping (>10,000 TEU) and mobile military vessels to provide ship-to-shore power capability.
Why ships? They don’t have great alternatives—the shipping industry is desperate to decarbonize. Hydrogen and ammonia are being explored, but come with serious downsides: low energy density, flammability, leaks, and massive infrastructure challenges. Fusion will provide a high-energy-density, long-range solution without the same infrastructure challenges—once it works, of course!
One common question is, why not fission? Fission works technically, but not practically. Small Modular Reactors (SMRs) could power ships, but licensing fission reactors on land is already brutally hard and expensive—doing it for vessels moving between international ports with enriched uranium is nearly impossible. Public perception is another major barrier: if we’re deploying thousands of nuclear reactors globally, they need to be meltdown-proof. Fusion is the only way to guarantee that. Regulation also isn’t as bad. While fusion won’t be a walk in the park to license, the NRC has declared a distinct framework for it—more like particle accelerators and hospitals than nuclear power plants. That’s a game-changer.
Instead of a 500+ MW grid-scale reactor, our system is 25 MWe, designed for ship propulsion. Our tokamak is roughly JET-sized, but with HTS magnets (8-9T) and higher plasma current (~10MA). The first-wall power flux is down from multi-MW/m² to nearly 500 kW/m²—still tough, but not nightmare mode. The materials challenges associated with the first wall and nuclear activation of the structures is greatly reduced. Also, ships don’t require 90% uptime like grid power plants. Downtime for maintenance is part of normal operations, making this a far more forgiving early application of fusion, unlike the grid where every down hour is lost revenue.
Jason and I come from SpaceX and Tesla, where we solved hard engineering problems at scale. My background is nuclear engineering (NC State, BS) and plasma physics (Columbia University, MS). We’ve been busy during our time in YC making technical progress on our reactor design, and are in the process of assembling a team of engineers who can pull this off.
This is a ridiculously hard problem, of course. But we think it’s the right hard problem—one that’s actually solvable (and worth solving!) with today’s tech if applied correctly. Eventually the cheaper and more robust SOAK and NOAK (second-of-a-kind and nth-of-a-kind) reactors will arrive in the coming decades (2050-2060) and then we'll pivot to decarbonising the grid and saving the world (we'll need to change our name), but until then we'll be out in the ocean!
Would love to hear your thoughts—whether you’re deep into plasma physics and engineering, skeptical-but–curious, or convinced it will never work . Ask us anything!