“It’s such a smooth ride, you can sit there and drink your coffee going through six-foot swells."
That's how one person recently described a trip on a newly patented stealth watercraft, Ghost. Ghost is a supercavitating boat—possibly the first in the world—which means it funnels a stream of air around its underwater propellers, enclosing them in a bubble. This drastically reduces drag, allowing the boat to achieve super-fast speeds.
But headlines today announced Chinese scientists are working on a submarine that would use supercavitation not for defense, but civilian transportation. The researchers envision an underwater trip from Shanghai to San Francisco that would last about 100 minutes, where the supercavitational air bubble encloses not just the propellers (as with Ghost) but the entire vessel.
Manned supercavitional crafts have been a huge challenge in the past. To enable supercavitation, an object has to already be traveling at speeds that have still never been achieved by modern submarines. There's also the trouble of steering, since inside a bubble, the rudders and other navigational mechanisms would have no contact with the water.
Li Fengchen, a professor of fluid machinery and engineering, told the South China Morning Post that the team has created a fresh solution to those problems. He says they've successfully cut down on that minimum speed by showering a special liquid membrane on the surface of the craft during the beginning of its trip. As for steering, says Li, the issue could be solved by fine-tuning where the membrane coats the craft.
"Our method is different from any other approach," Li said. "By combining liquid-membrane technology with supercavitation, we can significantly reduce the launch challenges and make cruising control easier."
Such a drag-reducing advance would be a significant step for submarine technology, as today's fastest vessels top out at a meager 40 knots (about 46 mph). But just how feasible is that less-than-two-hour trans-Pacific journey? Well, don't hold your breath. That calculation was based on the fastest theoretical speed of any supercavitating bubble, which is to say, the speed of sound— about 3,600 mph. As Ryan Faith at Vice News clarifies,
The difference between the speed at which physical laws of nature mandate your destruction and the ability to go anywhere near that fast is rather vast. Would it be possible to ride a submarine across the Pacific in 100 minutes? Sure, in much the same way it would be possible to ride an aircraft traveling at 90 percent the speed of light across the Pacific in a few hundredths of a second.
So maybe no civilian torpedo-sub for awhile. I never thought I'd say it, but we might actually see California's bullet train operating first.