The steam rapidly cools, collapses, and creates a void in the water. Water rushes through the ring to fill the void, propelling the boat. A controlled amount of air is supplied into the area of low pressure to improve efficiency.

The company says the drive will now achieve efficiency levels of around 12.7% at operating pressures, temperatures and flows, which is equivalent to a 2-stroke, carburetted outboard.

CEO John Heathcote told BB that its presentation at the Royal Institution of Naval Architects' Environmental Sustainability seminar early last month went very well.

"It elicited an awful lot of interest, " he said. "It has an lot of environmental implications in terms of application as we move the technology forwards.

I think it addresses a lot of issues that concern people right now."

Strangely, the recreational marine industry has been reluctant to beat a path to the Pursuit Dynamics door. "The interest generated has been minimal, " said Heathcote.

The company says the system will have a number of significant advantages over existing marine propulsion systems.

It will be cheaper to manufacture and maintain, lighter in weight, safer, quieter, environmentally friendly and, with further development, more efficient than existing recreational and light commercial marine propulsion systems, says Pursuit.

The company now believes that the identification and adoption of a suitable steam generator is the last significant challenge to bringing the Pursuit Marine Drive to market.

"Hitting the 2-stroke efficiency level is an important milestone for us as it clearly demonstrates that our technology has the potential to be commercially viable, " said Heathcote.