Launch HN: Maritime Fusion (YC W25) – Fusion Reactors for Ships
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!