The water fern salvinia molesta is extremely hydrophobic, surrounding itself by a flimsy skirt of air that prevents the plant from coming into contact with liquid. This inconspicuous plant could allow ships to have a 10 percent decrease in fuel consumption.

Researchers at the University of Bonn, Rostock, and Karlsruhe in Germany have now discovered how the fern does this. Their results can possibly be used for the construction of new kinds of hulls which glide through the water in an envelope of air. Such kinds of ships would get by with significantly less fuel due to decreased friction.

Materials researchers call the water fern's behavior 'superhydrophobic'. This property is of interest for many applications such as rapidly drying swimsuits or simply for fuel-efficient ships. Meanwhile, it is possible to construct superhydrophobic surfaces modeled on nature. However, these replicas have a disadvantage: the layer that forms on them is too unstable. In moving water it disappears after several hours at the latest.

The researchers from Bonn, Rostock, and Karlsruhe have now deciphered the trick the water fern uses to pin down its airy skirt. It has been known for some years now that on the surface of its leaves there are tiny whisk-like hairs. These are hydrophobic and keep water in the surroundings at a distance.

"We were able to show that the outermost tips of these whisks are hydrophilic, i.e. they love water," Professor Wilhelm Barthlott from the University of Bonn explains. "They plunge into the surrounding liquid and basically staple the water to the plant at regular intervals. The air layer situated beneath it can therefore not escape so easily."

Professor Barthlott is head of the Nees Institute of Biodiversity of Plants in Bonn. The experiments began there, which are continued today in conjunction with the Chair of Fluid Dynamics at the University of Rostock and the Institute of Applied Physics at the University of Karlsruhe.

"After the solving of the self-cleansing of the lotus leaf twenty years ago, the discovery of the salvinia effect is one of the most important new discoveries in bionics," Professor Thomas Schimmel from the University of Karlsruhe says.

Up to now, with container ships more than half of the propulsion energy is lost through friction of the water at the hull. With an air layer this loss could be reduced by ten percent according to the researchers' estimate. Since ships are huge fuel guzzlers, the total effect would be enormous. "Probably one percent of the fuel consumption worldwide could be saved this way" says Professor Barthlott.

(University of Bonn)