This startup wants to build a fusion reactor on a boat

Although only one fusion device on the planet has been able to meet important scientific standards, Maritime Fusion CEO Justin Cohen is already preparing to put a fusion reactor on board a boat.

Please listen. That’s not entirely outlandish. Thanks to advances in AI, computing, and superconducting magnets, fusion power generation is closer to commercialization than ever before. Convergence is increasingly looking like a matter of “when” rather than “if.” And once that happens, it promises to provide vast amounts of clean electricity from an abundant fuel source: water.

It is not necessarily unreasonable to install nuclear reactors on ships. Today, submarines and aircraft carriers equipped with nuclear fission reactors routinely navigate the oceans. It’s quiet, powerful, and can operate for decades before needing to be refueled. In the 1960s and 1970s, the idea of ​​nuclear-powered cargo ships was also explored in the private sector.

“Nuclear fission has definitely paved the way when it comes to nuclear power for ships,” Cohen, co-founder of Maritime Fusion, told TechCrunch.

Fusion promises to provide similar capabilities for ships, but without the concerns of meltdown, proliferation, and radiation. For now, the department is focused on building the first nuclear reactor on land. “I believe we were the first people to really look at what it would be like to put a tokamak on a ship,” Cohen said, referring to cutting-edge fusion reactor designs.

If fusion is successful, Maritime will take the leap into the oceans and be ahead of the curve. Moreover, from a business perspective, Cohen argues, it may actually be easier to start at sea.

The first fusion power plants won’t be cheap, and it will take time for costs to come down.

“Competing with things like solar and wind on the grid is very difficult from a cost standpoint,” Cohen said.

At sea, the economic situation looks different. Ammonia and hydrogen are good candidates to replace diesel and bunker fuel on cargo ships, but they are still quite expensive.

“These are some of the other very expensive fuels, and in fact, there may not be anything else as expensive as the world’s first nuclear fusion,” Cohen said. “In those cases, we actually compete head-to-head.”

To flesh out the concept and begin manufacturing parts for its first reactor, Maritime Fusion has raised $4.5 million in a seed round led by Trucks VC with participation from Aera VC, Alumni Ventures, Paul Graham, Y Combinator, and several angel investors, the startup exclusively told TechCrunch. The company was part of Y Combinator’s Winter 2025 batch.

Cohen said Maritime began assembling high-temperature superconducting (HTS) cables from tape purchased from suppliers, mostly Japanese companies. These cables will eventually form the basis of the powerful magnets the tokamaks need to confine the plasma needed for fusion reactions. It will also be sold to other companies for profit as Maritime develops the power plant.

The company expects the first power plant, named Ginmori, to generate about 30 megawatts of electricity.

Some of the biggest engineering challenges will be designing the support systems that harvest energy and keep the tokamak running, Cohen said. He said some ancillary work, such as fuel processing, will be done onshore to simplify onboard equipment.

The first Maritime tokamak will be about 8 meters in diameter, and the startup expects it to be operational in 2032 and cost about $1.1 billion.

For comparison, Commonwealth Fusion Systems (CFS), which is largely considered to be the leader in the fusion race, is building a small tokamak-shaped Spark just under 5 meters in diameter. The company has raised about $3 billion so far, much of it to build a demonstration plant that is expected to go online next year.

Sparc does not provide power to the grid. Instead, the goal is to prove that tokamaks can generate more power than they consume. CFS’ full-scale grid power reactor “Ark” is not scheduled to be completed until the early 2030s.

CFS has a significant head start over many fusion startups, including newcomer Maritime. But Cohen is confident that will not be an obstacle.

“We’re not going to spend billions of dollars on break-even equipment that doesn’t produce energy on the grid,” he said. “The first tokamak we build will be a tokamak that generates energy for our customers.”