Slippery Like A Fox.

This is some pretty crazy engineering. Some ship builder was staring at the tiny bubbles in his champaign and it hit him: bubbles make everything better.
Most hull designs are focused on reducing wave resistance and pressure drag (pushing water out of the way and escaping the vacuum the ship creates). But the other type of drag that's been on designers' minds is frictional drag. This is the force created by water sticking to the bottom of the boat and is the reason for those expensive Teflon bottom paints. But there are a variety of techniques that are like making the boat float on a cushion of air.

First, the Japanese are working on Microbubbles. A layer of bubbles that adheres all around the hull and taking advantage of the low viscosity to move the ship with less friction and turbulence. But right now it appears to only work at lower speeds.

Then there's the Americans who are doing tests on scale and computer models. They're also examining microbubbles and are very pleased with the efficience -for the speed. But this is DARPA and slow moving Navy ships just isn't sexy enough for them. So they're looking at other options like polymer lubricants and water repellent hull coating.

But its the Russians who look like the front-runners in this quest with their air cavity drag reduction. It involves using pumps to keep a pocket air in the ship, providing an excellent lubricant. The Russians who developed supercavitation for high-speed torpeedoes have been building ships that employ this technique for 25 years.

• Slippery ships float on thin air - mech-tech - 18 February 2006 - New Scientist Tech