Thrillseekers can get the same kind of high-speed ride from jet skis and speed boats that they can from high-performance race cars. But just like for vehicles on terra firma, speed on the water comes at great cost.
That's because traditional propeller-equipped engines aren't terribly fuel efficient at high speeds, while fast-spinning blades can become entangled with underwater plant life.
What's more, leaky oils and fuels from the engine can pollute the water, while the blades pose a threat to passing marine life.
But now Pursuit Dynamics PLC in Royston, England, says it has a new type of propulsion system to address those problems. Described as an "underwater jet engine," what literally makes this engine a blast is that it's powered primarily by centuries-old technology — steam.
The company is still waiting for patents on its engine design and won't comment exactly on how the Pursuit Marine Engine works. But Mike Todman, chief technical officer for the company, says it's based on work done by Alan Burns, an Australian engineer who invented the concept and sold the design to Pursuit Dynamics.
How to Steam-Power a Jet Engine
The principles of the propulsion system are apparently simplicity itself.
A separate boiler heats water to generate steam, which is pushed at about four times normal atmospheric pressure through a hollow tube submerged in the water.
When the steam hits the water, it immediately condenses to 1,600th of its previous volume. The resulting effect is a dramatic drop in pressure — essentially a vacuum — that sucks water from the front to the back of the tube and thus produces thrust to move.
But Todman says what makes the Pursuit engine unique is a specially designed chamber in the tube. The proprietary design forces the steam and water to react with air drawn from the surface.
According to Todman, the tube's design creates miniature "supersonic shockwaves" when the elements combine, resulting in what he says is significantly improved thrust energy produced from the steam.
The company claims the prototype units developed over the past three years show promising results. A roughly 7-inch-long test unit with an opening of less than three inches produced about 30 horsepower of thrust — enough to power a small speedboat.
Clear Advantages Claimed
Aside from the powerful thrust, Todman says the system offers other advantages, too.
Unlike traditional motors, for instance, the steam jet doesn't leak harmful fuel or oil into the water. And without moving parts, it's much quieter and easier to maintain than the outboard motors used in speedboats today.
Also, the company claims its proposed engine would be much safer for sea life. The water that emerges from the thrust engine is no more than 9 degrees Fahrenheit warmer than the water it takes it, so there's no danger of scalding.
And unlike regular outboard motors, there's no danger a spinning propeller would chew up submerged animals such as manatees.
John Heathcote, CEO of Pursuit Dynamics, says the company has been talking to "several companies" to further develop the engine for commercial use. He envisions, for example, that the device could be scaled up for use as a secondary engine in larger ships.
But he admits for now there are still limitations in producing a Pursuit Marine Engine for smaller boats. Chief among the concerns is finding or producing a steam generator small enough for use in a rubber dinghy, says Heathcote.