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Connecticut’s Electric Boat is working on a submarine that could make 100 knots submerged
01:00 AM EST on Tuesday, November 25, 2008
BY JOHN E. MULLIGAN
Journal Washington Bureau
WASHINGTON — Imagine a craft that could make 100 knots underwater, with a propulsion system so compact and powerful that it would leave ample room for payloads — small combat teams bound for missions on the shore, for example.
Electric Boat, the Groton, Conn.-based submarine builder, is part of a team that won a Pentagon contract to explore the high-speed sub two years ago. The progress has been encouraging enough to make it possible that such a craft will move from the research labs to open-water testing as early as 2010. Much of the research work is being conducted at Pennsylvania State University’s research testing facilities.
Major obstacles must be surmounted before the Underwater Express, as the experimental program is known, can be considered for production, according to Kevin J. Poitras, EB’s vice president for engineering and design programs. But the concept shows enormous promise for both military and commercial mariners.
Some experts have described the challenge of the Underwater Express as comparable to the technological leap that took aviation from propeller-driven planes to jets — extremely difficult to perfect, but extremely rewarding.
The project is, in a sense, a fresh attack on a limitation of physics that is familiar to anyone who has walked from the beach to go wading in the shallows. The drag resistance of water — orders of magnitude greater than that of air — really slows you down.
Shipbuilders and naval engineers have gone at the problem for centuries, improving speed through, and under, the water by refining different forms of propulsion, hull shape and construction materials that cut down on a vessel’s friction with the sea.
Modern advances have included space-age coatings, such as polymers, on the skin of vessels, and the creation of a sheath of tiny bubbles to reduce drag around the surface of the craft. The Underwater Express takes off from a theory developed by an American scientist in the 1960s: supercavitation.
Supercavitation (it comes from the same root as the word “cavity”) is a way to cut down on the friction between an object and the surrounding water by enveloping the object in a huge bubble of gas.
During the 1980s, the Soviet Union used supercavitation to produce the Shkval torpedo — essentially an underwater rocket capable of a top speed above 170 knots, according to the Pentagon agency that commissioned the Underwater Express contracts with EB and a competitor, a unit of Northrup Grumman in Annapolis, Md.
The Defense Advanced Research Projects Agency (DARPA) gave EB, a division of General Dynamics, a contract in November 2006 to total about $43 million with options. EB’s Poitras explained at an industry convention near Washington last month that the basic assignment was to develop a sub “that could go 100 knots underwater, with a propulsion system that would leave at least 50 percent of the vessel’s volume for payload.”
A vessel that could make 100 knots underwater would have dramatic implications for war fighting and commerce. One hundred knots is more than twice the speed of the fastest submarine on record, the Soviet Papa-class sub, according to naval analyst and author Norman Polmar. The speed of the fastest U.S. sub, Seawolf, is secret, but Polmar wrote last year that a top Navy official said during its construction that it would be able to go 35 knots.
If the Underwater Express is ever produced, it could provide an alternative to the Mark V, a 40-knot boat that Navy Sea, Air, Land teams (SEALs) use for transport. That craft has limitations that can’t be controlled: it can be seen and detected by radar and waves make for a difficult ride at high speed or, in very bad weather, cancel missions.
Eventually, DARPA envisions a 60-ton craft, 8 feet in diameter.
DARPA said in its proposal that it wanted builders “to determine the feasibility for supercavitation technology to enable a new class of high-speed underwater craft for future littoral missions that could involve the transport of high-value cargo and/or small units of personnel.”
The goal was a scale prototype that could give “a credible demonstration” to prove that “a supercavitating underwater craft is controllable at speeds up to 100 knots.”
Control is one of the toughest tasks, according to Poitras. “You have to be able to turn,” he said.
Another big problem, experts say, is noise. The quieting technologies of modern submarines add up to the invaluable battle asset of stealth. DARPA has noted, too, that there would be great difficulties with communications, and with sonar and other sensing tools essential to submarines.
But many of those problems would be tackled later — if and when the shipbuilders demonstrate that the Underwater Express is feasible.
If progress on the vessels continues as it has to date, said Poitras, a new phase of open-water testing could begin in early 2010.