Japanese researchers say they have found a way of generating electricity from the flow of seawater, writes David McNeill.

Cast your mind back to the cold war Hollywood thriller The Hunt for Red October (1990). Russian Capt Marko Ramius betrays the motherland by stealing an experimental submarine, killing his political officer and defecting to the west. Sean Connery and Alex Baldwin may have captained the film, but the real star was the sleek, silent submarine.

Driven by a revolutionary propulsion system, the fictional stealth machine struck fear into the US military by giving the Soviets the edge in underwater warfare. In reality, Russia and China tried but failed to develop such a craft, which has been bandied about in marine laboratories since at least the early 1960s. Now Japanese researchers claim to have put a radical new spin on an old technological quest.

Dubbed magnetohydronamics (MHD) - combining the words magnet, hydro for water and dynamics for movement - the technology is based on the principle that seawater (which contains salt) conducts electricity.

The search for a submarine propulsion system involved using superconducting electromagnets to send an electric current through seawater. The momentum comes as the water veers away from the current.

Push that water out fast enough through a duct and it will propel a vehicle. Hence the famed "silent drive": an engine with no moving parts.

But the experiments failed on various counts. The cost of generating the energy needed to power the superconducting magnets and propel the craft made the MHD system prohibitively expensive, and it was so much slower than conventional engines: The first working prototype ship - the Yamato 1 - built by Japan in the early 1990s and driven by two MHD thrusters managed just 15km per hour.

Enter Prof Minoru Takeda of Kobe University's Faculty of Marine Sciences. He and a team of scientists modified the Yamato blueprints using what they call a helical superconducting thruster, a design that they claim saves power and generates a much more intense electrical field than previous attempts. Then, they turned the entire experiment on its head: Instead of sending an electric current through seawater, they used seawater to make electricity.

The team claims to have developed an MHD power generation system that produces electricity using seawater flow combined with an external magnetic field. The system relies on the same principle as the superconducting electromagnetic thruster but reverses it, and applies the helical magnets to squeeze the most amount of electricity from the moving liquid.

Prof Takeda says the team has already proved that the system generates more power than it uses to run the powerful magnets - the most crucial technological hurdle.

They have built a small MHD power generation system in the sea around Kobe and are now working on a bigger model in a bid to improve the electricity yield.

The research suggests two promising leads. If work on the propulsion system succeeds, it could lead to the development of next-generation ships: quiet, efficient and non-polluting.

"A superconducting electromagnetic ship . . . has multiple advantages, such as reduced levels of operational noise, vibration and gas emission" wrote Prof Takeda in an academic paper outlining the technology. But while he stresses that the technology is still immature, it is the prospect of generating power from the sea that really excites his team.

"We're still at the basic research stage, collecting data on the principles behind our experiments. But it has a lot of potential and we're hoping that the state will back this work. It could eventually be added to other clean technologies such as wind and wave power."

So far, the Japanese government has shied away from major funding for such experiments. Most cutting-edge research in Japan takes places in corporate laboratories and universities have long been poorer second cousins. But despite recent cutbacks in funding for third level education, a radical reappraisal of the country's underfunded clean energies could be in the cards.

Japan currently relies for the bulk of its power generation from Middle East oil, supplemented by 55 nuclear reactors, which generate about a third of the country's electricity needs.

Both methods are controversial. The rising cost of oil has hit Japan's industrial productivity hard. And a previously unknown seismic fault, discovered beneath Japan's largest nuclear plant after a deadly earthquake struck Niigata in July, has thrown the country's entire nuclear programme into doubt.

With a prime minister apparently converted to the need to cut greenhouse gases, the word is going out: Japan must find new ways of meeting its power needs.

"We think that our time has come," said Prof Takeda. "This sort of natural energy is our hope for the future."