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http://www.xconomy.com/boston/2012/06/21/juliet-marines-ghost-ship-emerges-from-stealth-startup-gears-up-for-war/?single_page=true%E2%80%9D
6-21-2012


About an hour north of Boston, in a city by the sea, there’s a project underway to reinvent the marine industry. More specifically, the marine defense industry.

Imagine a boat that moves through the water differently from any other boat in existence. It uses “supercavitation”—the creation of a gaseous bubble layer around the hull to reduce friction underwater—to reach very high speeds at relatively low fuel cost. Its speed and shape means it can evade detection by sonar or ship radar. It can outrun torpedoes. Its fuel efficiency means it has greater range and can run longer missions than conventional boats and helicopters.

Now imagine that this vessel has already been built and tested. It “flies” through the water more or less the way it was designed to—like a high-tech torpedo, except part of the craft is above water—and it can be maneuvered like a fighter plane. “It’s almost as much an aircraft as it is a boat,” says its inventor, Gregory Sancoff, the founder and CEO of Juliet Marine Systems, a private company in Portsmouth, NH.

The vehicle, dubbed the “Ghost,” is the first of its kind and is garnering attention from organizations like the U.S. Navy, Coast Guard, defense contractors, and foreign governments—as well as hackers in foreign countries, who are presumably trying to figure out how it works. Juliet Marine Systems has received about $10 million in total funding, about half of which comes from its founder and private investors. The startup’s institutional investor is Avalon Ventures, a VC firm with offices in the San Diego and Boston areas.

Until recently, the project was kept under wraps because of secrecy orders from the federal government. But this summer, Sancoff says, the Ghost—which looks like something out of Star Trek (see photos)—will be ready for prime-time deployment. His team of 16 employees is working on integrating weapons and sensors for military missions. “We have a fully functional, basically go-to-war boat right now,” Sancoff says.

The question is, does it really work? And, more to the point, can it be used for missions safely, reliably, and effectively? If the answer is yes—and that’s a big if, from an outside perspective—one could imagine a squadron of Ghosts being deployed to the Persian Gulf, say, to defend warships and other interests against “swarm” attacks by small boats, Sancoff says. The vessel also could be used against pirate attacks, for Coast Guard rescue missions, or to transport workers to and from oil platforms. The technology might have much broader uses, too—in global cargo shipping, for example, to reduce fuel costs, or for commercial jet skis. (Wacky as it is, the concept is not as far-fetched as, say, a submarine that can also fly.)

But to get a better sense of the ship’s real prospects—and the company’s—let’s consider the whole story.

From Medical to Marine Tech

Sancoff, 55, is a prolific inventor and serial entrepreneur who, I’m told, takes engineering magazines to bed. He grew up in a military family and went to high school in Lawrence, MA. As a kid, he lived on Army bases and says he remembers saluting the flag when he got out of the car. Sancoff never served in the military, but that’s probably because he was too busy inventing stuff.

He started his first company when he was 18—a machine shop for doing rapid device-prototyping for other businesses. He sold that and headed west to San Diego in 1982, at age 25. As a consultant, he became an expert in medical devices, including systems for delivering intravenous fluids, collecting health data, and other applications. He started a new company, Block Medical, and sold it for $80 million in 1991. His next company, River Medical, was based around a new kind of drug-delivery device for hospitals. River acquired IVAC, a medical-device firm divested from Eli Lilly, and ended up being sold to Advanced Medical (IMED) for $400 million in 1995.

Sancoff’s next big project was to start Onux Medical, a surgical tech company based in New Hampshire. It was there, in 2000, that he first got inspiration for Juliet Marine and the Ghost ship. Sancoff was sitting in a conference room when he heard the U.S.S. Cole had been attacked off the coast of Yemen by a small boat loaded with explosives. Seventeen U.S. sailors had been killed and many more wounded. He sat there in disbelief as he realized a billion-dollar warship had nearly been sunk by a couple of guys in a raft.

Juliet Marine would derive its name from a U.S. Navy “war games” exercise held in 2002. At $250 million, it was the most expensive exercise in Naval history. “Fleet Battle Experiment—Juliet” involved warships parked off the coast of California and a series of simulated small-boat attacks. The results of the simulation were grim: more than 20,000 deaths and massive losses to the fleet, in a Persian Gulf scenario. Yet, Sancoff says, the Navy hasn’t done anything in the past 10 years to guard against such attacks, other than work on targeted rocket systems.

“When you’re an entrepreneur, there has to be an overwhelming reason why you do it,” Sancoff says. “That was it for me.”

He saw a big opportunity—if only he could design a ship fast enough and maneuverable enough to intercept attackers before they could get close to big ships or shorelines. He had raced hydroplanes as a teenager—probably could bulls-eye womp rats, too (sorry, Star Wars joke)—so he had an intuitive feel for what it might take.

Which brings us to supercavitation. It’s an old idea. During the Cold War, the Russians developed a torpedo called the Shkval (“squall”) that could go more than 200 mph — five times as fast as a conventional torpedo — using a rocket engine and air ejected in front to produce a gaseous bubble completely enveloping the projectile. That reduces the friction between the hull and its surroundings by a factor of about 900, enabling superfast travel. Yet rocket-propelled torpedoes have downsides in performance and reliability; the sinking of the Russian submarine Kursk in 2000 is rumored to have been caused by a malfunctioning Shkval.

Meanwhile, the U.S. Navy and others reportedly have been working on a next-generation supercavitating torpedo since at least the 1990s. And in recent years, the Defense Advanced Research Projects Agency (DARPA) ran a program, called Underwater Express, to design a supercavitating submarine. There is also interest in using the concept to improve fuel efficiency for oil tankers, ferries, and other large ships, typically by creating air bubbles at the front of the hull. As of yet, however, nobody has publicly demonstrated a successful supercavitating craft.

To that end, after leaving Onux (which was bought by Bard in 2004), Sancoff spent several years doing research on his own and incorporated Juliet Marine in 2008. By June of last year, using $5 million of mostly his own money, his team had built a fully functioning prototype — Sancoff prefers the term “pre-production” vehicle. And earlier this year, he secured an additional $5 million from Avalon Ventures, the VC firm that invested in his last two companies.

At a Bay Area event in March, Kevin Kinsella, the Avalon partner on the deal, spoke glowingly of River Medical in particular. “We got 10x [return] in 18 months, and I only had to go to four meetings. An ROI of 2.5x per board meeting is fantastic,” he said. (Onux didn’t cash out quite as well, but it still worked out fine.)

After seeing firsthand what Juliet Marine built with $5 million, Kinsella said, “If you were taken around by a handler from Lockheed or Grumman or Northrop or any of them, and they told you, ‘We developed this on $150 million,’ you wouldn’t bat an eye.” He told the story of a meeting with Avalon and its fund investors. Someone asked Sancoff, “How did you get to be so capital efficient in your company?” Kinsella relays, “He leaned on the podium and said, ‘Because it was my money.’”

Not Your Grandfather’s Boat

OK, so here’s how it works, according to a patent filing (see diagram, below). The main compartment of the Ghost vessel, which houses the cockpit and controls, sits above the water in between two torpedo-shaped pontoons or “foils,” which are submerged and create all the buoyancy and propulsion for the craft. The angle of the struts that connect the foils to the command module is adjustable — so the craft can ride high in choppy seas and at high speeds (so waves don’t hit the middle part), and low in calm water and at lower speeds.

“We’re basically riding on two supercavitating torpedoes. And we’ve put a boat on top of it,” Sancoff says.

At the front of each foil is a special propeller system that pulls the craft forward. The propellers are powered by a modified gas turbine — a jet engine — housed in each foil; the air intake and exhaust ports for the engines are in the struts. As the ship moves through the water, the motion of the propellers creates a thin layer of bubbly water vapor that surrounds each foil from front to back, helped along by the presence of “air trap fins” that keep the vapor in contact with the hull (and keep liquid away from the hull). The vapor is what constitutes the supercavitation, so the foils can glide effortlessly through the bubbles.

“The key is the propulsion. You have to have a lot of power at the right location in this vessel,” Sancoff says. Exactly how this is done is a trade secret. But the propulsion system, which he says generates 30 percent more thrust than any other propeller-based system, essentially “boils water underwater and generates steam vapor.” (I take this to mean the pressure directly behind the propeller blades is so low that the liquid water there “boils” off and becomes a gas—hence the bubbles.)

After doing some digging in the literature, I asked Sancoff whether what’s in the patent filing is really how it works — in terms of how the Ghost creates its mysterious supercavitation. His answer: “No.” (OK, so there’s more to the story here. But you know when you’re supercavitating, he says, because the engine efficiency actually improves as you go faster.)

In any case, the overall design makes the craft go fast, but Sancoff isn’t making any public claims yet about exactly how fast. “We don’t talk about speed, how many weapons [it can carry], or how far we can go,” he says. Yet its rumored speed is at least 80-100 knots — over 100 mph. That’s not going to challenge the top speedboat records — there have been hydroplane efforts (riding on the water surface) that have exceeded 200 mph (174 knots) and even 300 mph (261 knots), some with fatal results—but the Ghost is faster than any previous underwater vehicle, Sancoff says.

What’s more, he says, the Ghost provides a much smoother ride than what Navy SEALs are used to; many of them blow out their backs from the bumpiness of their boats, he says. “Our boat does not have impact from the waves. We cut through the wave,” Sancoff says. “That is critical science.”

Hydrodynamics experts I’ve talked to say the main challenges of such a craft are controlling it, stabilizing it, and making it quiet. Going superfast in a straight line might be doable, they say, but any sort of turning or maneuvering must be done very carefully, because if the bubble layer distorts or breaks down at high speeds, tremendous water forces will come to bear on the foils, which can be catastrophic.

To steer itself through the water and maintain stability, the Ghost uses four movable flaps on the front of each foil and four on the back of each foil, for a total of 16 flaps. (The flaps reach through the thin bubble layer into the surrounding water.) The struts are adjusted to keep the command module out of the water, and the foils stay submerged, so waves at the water surface should only hit the struts, which have a small cross-section.

“It’s computer controlled, like a modern F-18,” Sancoff says. “We’re boring what looks like two wormholes underwater, and we’re flying through foam.” Sancoff himself has been test-driving the ship over the past couple of years. “I have been learning an entirely new craft since then. It’s a totally new experience,” he says. “Just because you drive Grandpa’s boat, you’re not going to drive this one. It’s more like a helicopter.”

As for the craft’s audio profile, Sancoff is proud of its “silent propulsion” system that includes a sophisticated muffler system for the engines. You can’t hear it from 50 feet away, he says.

Coming Out of the Night

With any grand invention like this, some outside experts are going to be skeptical. “I wouldn’t say it’s not going to work. But I have concerns,” says Gary Balas, head of the department of aerospace engineering and mechanics at the University of Minnesota. Balas is an expert in flight and underwater control systems, but his main objection is that the propulsion system of the Ghost, with its forward propellers, is very unusual for a supercavitating craft. The typical approach, as in the Russian torpedo, is to propel the craft from behind and eject gas and/or use a blunt shape in the front to create an air cavity around the craft. “I don’t see how they’ll achieve what they expect to achieve,” Balas says. “And I don’t see how they’ll control the altitude and the yaw of the vehicle.”

His colleague, Roger Arndt, also a professor at the University of Minnesota, is an expert in fluid flow and cavitation. He has doubts about the Ghost propulsion method as well. In fact, cavitation bubbles are normally bad for propellers and can cause serious damage. But there is a type of propeller, with wedge-shaped blades, that produces supercavitation in high-speed racing boats; presumably this is similar to Ghost’s propellers. But in this case, Arndt says, “I am dubious about the application of supercavitating propellers.” (To be fair, Sancoff said that what’s in the patent filing isn’t quite how it works.)

Other experts on supercavitation declined to comment for this article. Sancoff emphasizes that the project has a lot of sensitive aspects to it, in terms of national security, so people who know about it aren’t talking. And he claims that Juliet Marine’s website is getting “attacked” 350 times a month by hackers, mostly in foreign countries.

In any case, the current vehicle — which resides under tight security at Portsmouth Naval Shipyard (“a great asset” for a startup to be able to rent space in, he says) — holds 18 people and weighs some 60,000 pounds fully loaded; the underwater part of the vessel is 62 feet long. Sancoff says it can be launched from any beach. “A group of these boats coming out of the night in the Persian Gulf, armed with torpedoes, would be undetectable to large ships,” he says. “Ghost cannot be hit by a torpedo. You would have to shoot it with a gun.”

Not surprisingly, Sancoff sees an urgent military need for his craft. The Navy loses sleep about swarm attacks and security in the Strait of Hormuz (which runs between Iran, United Arab Emirates, and Oman) and other strategic waterways, he says. Yet it hasn’t moved quickly enough to do anything about the threats. “We talk with the Navy weekly,” he says. “We believe the U.S. could use a hundred of these boats right away.” At a price of $20 million per boat — fully loaded with electronics, radar, and so forth — that “provides us with a billion-dollar market opportunity for coastal and fleet protection,” he says.

Meanwhile, the U.S. State Department has granted Juliet Marine permission to talk with the governments of Israel and UAE, which both have marine security concerns. The company says it is currently building a manufacturing facility near Portsmouth, in anticipation of ramping up to sell Ghost ships to customers. Sancoff adds that Juliet Marine is planning to build two more versions of the ship this fall, using what he calls “the final configuration.”

And while the startup strives to gain full acceptance from the U.S. Navy and other potential defense customers, it is “working on weaponizing” the craft, says Sancoff. “The vehicle’s done. Now it’s time to get mission modules complete.” That means mounting torpedoes, machine guns, radar, mine-detection systems, and other sensors onto the craft — and making sure it all works the way it’s supposed to.

That remains to be seen, of course. But if it performs as advertised, Juliet Marine could end up playing a vital role in global security on the high seas. “That’s the beautiful thing about being an entrepreneur,” says Sancoff. “You take a risk with it.”

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http://www.nhbr.com/news/951153-395/n.h.-entrepreneur-puts-his-faith-in-a.html
Friday, February 24, 2012

'We plan to build a major company here,' says Greg Sancoff, founder of Juliet Marine Systems.

When entrepreneur Greg Sancoff takes his watercraft out for a test drive on the Piscataqua River, the 75-foot long vessel draws quizzical looks from people who see it. There are good reasons for the double-take stares.

The sleekly angled, supercavitating Ghost looks like it just arrived from the set of a Hollywood science fiction movie. In reality, the Ghost has the potential to play a vital role in protecting American Navy vessels in volatile regions of the world, such as the current, headline-making tensions in the Persian Gulf.

Ghost is a high-speed attack craft - Sancoff calls it a modern version of the PT Boat - specifically designed to protect vital waterways like the Straits of Hormuz and to counter threats to commercial shipping, such as piracy, which is increasing in many areas of the world.

Sancoff says the Ghost has been compared to an attack helicopter on the water. "Ghost would be a very important and cost-effective security tool to exert a constant presence in this troubled region," he said.

For almost three decades as a successful entrepreneur in the medical devices industry, Sancoff was accustomed to taking risks. He has founded and sold four companies totaling more than $100 million. But his latest venture, Portsmouth-based Juliet Marine Systems, required a combination investment of patriotism, personal finances and innovative research and development far beyond anything he had done before.

"By far this is the most fulfilling thing I have ever done," Sancoff said.

Fast, fuel-efficient

What makes the Ghost unique is that it was developed entirely on spec in less than four years, unprecedented for a potential "game-changing" defense technology, he said.

While other weapons and defense industry programs get government approval and research funding and then embark on lengthy development and deployment process, Juliet Marine Systems bypassed all of that.

"It was the fastest way to get it done. We didn't get involved with government research institutions because it would have slowed us down," Sancoff said of his personal multimillion-dollar backing of the Ghost. "Look at Silicon Valley and the most efficient way to develop new technology. We did this in a think tank environment just as companies like Apple do."

Juliet Marine Systems created and built the Ghost prototypes in secrecy at the Portsmouth Naval Shipyard with only 10 full-time engineers and scientists.

The Ghost could have been deployed already if the federal government had not put a secrecy order in place for more than 18 months on some of Juliet Marine's patents. Sancoff said this prevented extensive testing during that time because the craft couldn't be seen in public.

Despite the delay, Sancoff has built it and the Navy and maritime industry have come to see it.

What they are seeing is a very fast, fuel-efficient craft that can barely be detected by radar and can stay on patrol for a very long time (because it's now classified material, Sancoff can't say exactly how fast the craft can go and how long it can go between refueling its gas turbine jet engines.)

It's fast because it has been designed to fly through an artificial underwater gaseous environment that creates 900 times less hull friction than water. Sancoff also said the Ghost has 22 special systems that give the craft stability.

Juliet Marine is currently in discussions with defense companies to implement an off-the-shelf weapons solution. In keeping with his entrepreneurial roots, Sancoff will not make it a overthought process.

"We do not have to reinvent the wheel," he said. "There are several systems today that would provide ample power and fit the mission characteristics."

'Call to action'

During a recent visit to the Pentagon, a high-ranking naval research officer asked Sancoff, "Why did you do this?"

For Sancoff, it was a decades-long journey of finding a solution and "giving something back to my country."

The genesis, Sancoff explained, came in October 2000 when the naval destroyer USS Cole was attacked and 17 sailors killed by an explosive-laden small craft guided by al-Qaeda terrorists in Yemen. He became focused on a solution for fleet security from attacks that are akin to land-based IEDs, or improvised explosive devices.

The terrorist attacks of Sept. 11, 2001, provided another burst of motivation. Finally, there was a major naval fleet exercise in 2002 to determine security from small boat attacks. The exercise was code-named Juliet, which provided the name for Sancoff's company, and the result showed too many vulnerabilities.

"This was my call to action," he said.

He said he began to do voluminous research, and when he sold his Hampton-based company, Onux Medical, in 2004, it became his full-time quest to create a new type of company to work at rapid deployment speed.

"My wife Jennifer talked about this extensively. The idea was so strong that we decided to go forward and develop these ideas," Sancoff said about the decision to finance the multimillion-dollar startup with their money. "I have been very successful and wanted to give something back to my country."

The company was officially started in late 2007, and major research and development began in 2008 after the space at Portsmouth Naval Shipyard was secured. "We have a very small team of people, and they are very smart at what they do. This has allowed us to have such a rapid turnaround time," Sancoff said.

The company's board members include two retired U.S. Navy admirals and former U.S. Sen. John E. Sununu of New Hampshire. Sancoff said construction of the Ghost was enhanced by the work of many regional machine shops, and he believes the Seacoast region should become the site for manufacture of the Ghost and other marine-related systems.

In fact, the company has begun to add its engineering and scientific staff in anticipation of both commercial and military contracts for the Ghost.

"It's up to them (users) just how fast they want to adapt this new technology," Sancoff said. "We have been in discussions about making a 150-foot version. There are so many applications, even down to pleasure craft size. We plan to build a major company here."

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REFERENCE TO PENDING PRIOR PATENT APPLICATIONS

[0001] This patent application:

[0002] (1) is a continuation-in-part of pending prior U.S. patent application Ser. No. 12/485,848, filed Jun. 16, 2009 by Gregory E. Sancoff et al. for FLEET PROTECTION ATTACK CRAFT (Attorney's Docket No. JULIET-0102), which in turn claims benefit of:

(i) prior U.S. Patent Application Ser. No. 61/132,184, filed Jun. 16, 2008 by Gregory Sancoff for FORCE PROTECTION ATTACK CRAFT (Attorney's Docket No. JULIET-1 PROV); and

(ii) prior U.S. Patent Application Ser. No. 61/200,284, filed Nov. 26, 2008 by Gregory Sancoff et al. for FLEET PROTECTION ATTACK CRAFT (F-PAC) (Attorney's Docket No. JULIET-2 PROV);

[0005] (2) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/374,923, filed Aug. 18, 2010 by Gregory E. Sancoff for SUPERCAVITATION AIR CHANNELS FOR BUOYANT TUBULAR FOIL (Attorney's Docket No. JULIET-7 PROV); and

[0006] (3) claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/374,940, filed Aug. 18, 2010 by Gregory E. Sancoff for TORPEDO EMPLOYING FRONT-MOUNTED COUNTER-ROTATING PROPELLERS AND STEERING SPOILERS (Attorney's Docket No. JULIET-9-2-PROV).

[0007] The five above-identified patent applications are hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0008] This invention relates to marine vessels in general, and more particularly to high-speed attack and reconnaissance craft.

BACKGROUND OF THE INVENTION

[0009] The terrorist attack on the guided missile destroyer USS Cole in Aden harbor in 2000 provided a devastating example of what a small group of terrorists can do to a modern warship with minimal resources-in the case of the USS Cole, two terrorists in a small boat carrying a few hundred pounds of explosives came close to sinking a billion dollar warship.

[0010] The success of the attack on the Cole has given rise to another, even more disturbing concern-that a large number of high speed boats, each packed with explosives and manned by suicide bombers, could create a "small boat swarm" which could overwhelm the defenses of a warship, particularly in restricted waters where reaction time and maneuverability may be limited. Indeed, recent wargame simulations suggest that such swarm tactics could prove extremely effective against naval battle groups operating in the narrow waters of the Persian Gulf.

[0011] It is currently believed that such "small boat swarm" tactics are best countered with fast, similarly-sized, highly-maneuverable and heavily-armed attack craft which can establish a defensive perimeter at a safe distance from the naval battle group. To this end, appropriately-outfitted Zodiac-type craft have already been deployed for this purpose. However, experience has shown that Zodiac-type craft are only practical in the relatively calm waters of a harbor. This is because operating Zodiac-type craft at high speed in the turbulent waters of the open sea imposes excessive physical stresses on the crews that can only be withstood for short periods of time. Furthermore, the defensive perimeter should, ideally, be established at a substantial distance from the battle group (e.g., at least 10 miles out), in order to give the battle group sufficient time to react in the event that any of the small boat swarm should penetrate the defensive perimeter established by the Zodiac-type craft. However, due to their light construction, limited operating time at high speeds, and limited fuel-carrying capacity, Zodiac-type craft are not capable of maintaining a reliable defensive perimeter so far out from the battle group. In practice, with Zodiac-type craft, the defensive perimeter must generally be maintained much closer to the battle group, with the consequent loss of reaction time.

[0012] It has been suggested that attack helicopters might be used to protect a naval battle group when it is at sea or at anchor. However, attack helicopters generally have relatively limited range and, perhaps more importantly, relatively limited sortie time, which effectively prevents them from maintaining a reliable defensive perimeter a substantial distance out from the battle group. Furthermore, attack helicopters generally have substantial radar, infrared and visual "signatures", thereby making them relatively easy to detect and target.

[0013] Thus, there is a need for a new and improved fleet protection attack craft which can be used to maintain a defensive perimeter a safe distance out from a naval battle group. In this respect, it should be appreciated that such a craft should be small, fast, highly-maneuverable and heavily-armed. Furthermore, the craft should provide a stable platform even when running at high speed in substantial ocean swells, whereby to minimize physical stress on the crew and to provide a stable weapons platform. Further, the craft should be capable of remaining on station for a substantial period of time, in order to maintain a reliable defensive perimeter at a safe distance from the battle group.

[0014] There is also a need for a new and improved craft which can be used for reconnaissance, and/or to deliver small teams of special forces behind enemy lines and/or to extract the same. Thus, the craft should also be capable of "stealth mode" operation, i.e., it should have small radar, infrared, visual and noise signatures, thereby making it difficult to detect and target.

SUMMARY OF THE INVENTION

[0015] These and other objects of the present invention are addressed by the provision and use of a novel fleet protection attack craft. The novel attack craft is small, fast, highly-maneuverable and heavily-armed. The novel attack craft provides a stable platform even when running at high speed in substantial ocean swells, whereby to minimize physical stress on the crew and to provide a stable weapons platform. And the novel attack craft is capable of remaining on station for a substantial period of time, in order to maintain a reliable defensive perimeter at a safe distance from a naval battle group. Thus, the novel attack craft provides an effective means for defending against a "small boat swarm", by establishing a defensive perimeter at a safe distance from the battle group and thereby permitting the interception, identification, warning and, if ultimately necessary, destruction of hostile boats long before they can approach the battle group.

[0016] In addition, the novel attack craft is capable of "stealth mode" operation, i.e., it has small radar, infrared, visual and noise signatures, thereby making it difficult to detect and target. Thus, the novel attack craft also provides an effective means for conducting reconnaissance and/or for delivering small teams of special forces behind enemy lines and/or for extracting the same.

[0017] In one form of the present invention, there is provided a marine vessel comprising:

[0018] a command module;

[0019] first and second buoyant tubular foils; and

[0020] first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;

[0021] wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel;

[0022] wherein the first and second struts are pivotally connected to the command module and pivotally or fixedly connected to the first and second buoyant tubular foils, respectively; and

[0023] wherein the first and second struts comprise substantially rigid planar structures.

[0024] In another form of the present invention, there is provided a marine vessel comprising:

[0025] a command module;

[0026] first and second buoyant tubular foils; and

[0027] first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;

[0028] wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and

[0029] wherein the marine vessel further comprises first and second engines enclosed within the first and second buoyant tubular foils, respectively, and first and second propulsion units connected to the first and second engines, respectively, for moving the marine vessel through water.

[0030] In another form of the present invention, there is provided a marine vessel comprising:

[0031] a command module;

[0032] first and second buoyant tubular foils; and

[0033] first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;

[0034] wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and

[0035] wherein the marine vessel further comprises first and second propeller mechanisms mounted on the leading ends of the first and second buoyant tubular foils, respectively, for moving the marine vessel through the water.

[0036] In another form of the present invention, there is provided a marine vessel comprising:

[0037] a command module;

[0038] first and second buoyant tubular foils; and

[0039] first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;

[0040] wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and

[0041] wherein the marine vessel further comprises a plurality of spoilers mounted on the first and second buoyant tubular foils for steering the marine vessel as it moves through the water.

[0042] In another form of the present invention, there is provided a marine vessel comprising:

[0043] a buoyant tubular foil; and

[0044] a propeller mechanism mounted on a forward end of the buoyant tubular foil for moving the marine vessel through water.

[0045] In another form of the present invention, there is provided a marine vessel comprising:

[0046] a buoyant tubular foil; and

[0047] a plurality of spoilers mounted on the buoyant tubular foil for steering the marine vessel as it moves through water.

[0048] In another form of the present invention, there is provided a marine vessel comprising:

[0049] a buoyant tubular foil;

[0050] a propeller mechanism mounted on a forward end of the buoyant tubular foil for moving the marine vessel through water; and

[0051] a plurality of spoilers mounted on the buoyant tubular foil for steering the marine vessel through the water;

[0052] wherein each of the spoilers comprises a plate movable between (i) an inboard position wherein the plate is substantially aligned with a skin of the buoyant tubular foil to which the spoiler is mounted, and (ii) an outboard position wherein the plate projects into, and deflects, water flowing by the buoyant tubular foil to which the spoiler is mounted.

[0053] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0054] providing a marine vessel comprising:

a command module;
first and second buoyant tubular foils; and
first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;
wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel;
wherein the first and second struts are pivotally connected to the command module and connected to the first and second buoyant tubular foils, respectively;
wherein the first and second struts comprise substantially rigid planar structures;

[0061] moving the marine vessel through water; and

[0062] adjusting the position of the first and second struts relative to the command module.

[0063] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0064] providing a marine vessel comprising:

a command module;
first and second buoyant tubular foils; and
first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;
wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and
wherein the marine vessel further comprises first and second engines enclosed within the first and second buoyant tubular foils, respectively, and first and second propulsion units connected to the first and second engines, respectively, for moving the marine vessel through the water; and

[0070] moving the marine vessel through the water.

[0071] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0072] providing a marine vessel comprising:

a command module;
first and second buoyant tubular foils; and
first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;
wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and
wherein the marine vessel further comprises first and second propeller mechanisms mounted on forward ends of the first and second buoyant tubular foils, respectively, for moving the marine vessel through the water; and

[0078] moving the marine vessel through the water.

[0079] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0080] providing a marine vessel comprising:

a command module;
first and second buoyant tubular foils; and
first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;
wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and
wherein the marine vessel further comprises a plurality of spoilers mounted on the first and second buoyant tubular foils for steering the marine vessel as it moves through the water; and

[0086] moving the marine vessel through the water and adjusting positions of the spoilers.

[0087] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0088] providing a marine vessel comprising:

a buoyant tubular foil; and
a propeller mechanism mounted on the leading end of the buoyant tubular foil for moving the marine vessel through the water; and

[0091] moving the marine vessel through the water.

[0092] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0093] providing a marine vessel comprising:

a buoyant tubular foil; and
a plurality of spoilers mounted on the buoyant tubular foil for steering the marine vessel as the vessel moves through the water; and

[0096] moving the marine vessel through the water and adjusting the position of the spoilers.

[0097] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0098] providing a marine vessel comprising:

a buoyant tubular foil;
a propeller mechanism mounted on the leading end of the buoyant tubular foil for moving the marine vessel through the water; and
a plurality of spoilers mounted on the buoyant tubular foil for steering the marine vessel through the water;
wherein each of the spoilers comprises a plate movable between (i) an inboard position wherein the plate is substantially aligned with a skin of the buoyant tubular foil to which the spoiler is mounted, and (ii) an outboard position wherein the plate projects into, and deflects, the water flowing by the buoyant tubular foil to which the spoiler is mounted; and

[0103] moving the marine vessel through water and adjusting the position of the spoilers.

[0104] In another form of the present invention, there is provided a marine vessel comprising:

[0105] an elongated closed underwater vehicle;

[0106] first and second propellers mounted on a forward end of said vehicle and adapted in operation to move said vehicle through water;

[0107] said first and second propellers comprising leading and trailing propellers;

[0108] wherein said leading and trailing propellers are adapted to rotate in opposite directions to each other simultaneously;

[0109] whereby to provide propeller generated super-cavitated water flowing from the propellers and thence along an outer surface of said vehicle;

[0110] whereby to diminish friction on the outer surface of said vehicle and facilitate high underwater speeds.

[0111] In another form of the present invention, there is provided a marine vessel comprising:

[0112] an elongated closed underwater vehicle;

[0113] propeller means mounted on a forward end of said vehicle;

[0114] said propeller means being operable to move said vehicle through water and to produce super-cavitated water for flow aft of said propeller means and adjacent an outer wall of said vehicle;

[0115] whereby to effect a water pressure on the vehicle outer wall less than water pressure forwardly of said propeller means.

[0116] In another form of the present invention, there is provided a marine vessel comprising:

[0117] a command module;

[0118] first and second buoyant tubular foils;

[0119] first and second struts connecting said first and second foils to said command module;

[0120] wherein said first and second foils provide all buoyancy required for the vessel;

[0121] wherein said struts are each pivotally connected to said command module and to one of said foils;

[0122] said first and second struts comprising generally rigid planar structures; and

[0123] first and second propellers mounted on forward ends of said foils for moving the vessel through water;

[0124] wherein said first and second propellers comprise leading and trailing propellers; and

[0125] wherein said leading and trailing propellers rotate in opposite directions to create air skirts around the foils and extending along lengths of the foils to decrease foil surface friction.

[0126] In another form of the present invention, there is provided a marine vessel comprising:

[0127] an elongated closed underwater vehicle;

[0128] a propeller mounted on a forward end of said vehicle and adapted in operation to move said vehicle through water;

[0129] said propeller being of a size and configuration to provide propeller generated super-cavitated water flowing from said propeller and thence along an outer surface of said vehicle;

[0130] whereby to diminish friction on the outer surface of said vehicle and facilitate high underwater speeds.

[0131] In another form of the present invention, there is provided a method for moving through water, the method comprising:

providing a marine vessel comprising:
a command module;
first and second buoyant tubular foils; and
first and second struts for connecting the first and second buoyant tubular foils to the command module, respectively;

[0136] wherein the first and second buoyant tubular foils provide substantially all buoyancy required for the marine vessel; and

[0137] wherein the marine vessel further comprises first and second propeller mechanisms mounted on the forward ends of the first and second buoyant tubular foils, respectively, for moving the marine vessel through water; and

[0138] moving the marine vessel through water.

[0139] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0140] providing a marine vessel comprising:

a buoyant tubular foil; and
a propeller mechanism mounted on the forward end of the buoyant tubular foil for moving the marine vessel through the water; and

[0143] moving the marine vessel through water.

[0144] In another form of the present invention, there is provided a method for moving through water, the method comprising:

[0145] providing a marine vessel comprising:

a buoyant tubular foil;
a propeller mechanism mounted on the forward end of the buoyant tubular foil for moving the marine vessel through water; and
a plurality of spoilers mounted on the buoyant tubular foil for steering the marine vessel through water;
wherein each of the spoilers comprises a plate movable between (i) an inboard position wherein the plate is substantially aligned with a skin of the buoyant tubular foil to which the spoiler is mounted, and (ii) an outboard position wherein the plate projects into, and deflects, water flowing by the buoyant tubular foil to which the spoiler is mounted; and

[0150] moving the marine vessel through water and adjusting the positions of the spoilers.

[0151] In another form of the present invention, there is provided an elongated tubular foil for travel through water, the foil being provided with a propulsion means;

[0152] said propulsion means comprising in part a propeller means rotatably mounted on a forward end of the foil and adapted to move the foil through the water;

[0153] said propeller means being adapted to effect supercavitation of water while operative to move the foil through the water;

[0154] to thereby create a skirt of supercavitated water adjacent at least a portion of an outer skin of the foil;

[0155] such that the foil moves through the skirt of supercavitated water.

[0156] In another form of the present invention, there is provided a method for propelling a body through water, the method comprising the steps of:

[0157] providing the body in an elongated tubular configuration having a propulsion means rotatably mounted on a forward end of the body and adapted to move the body through the water;

[0158] activating the propulsion means so as to effect the movement of the body through the water and so as to create a skirt of supercavitated water adjacent at least a portion of an outer skin of the body;

[0159] such that the body moves through the supercavitated water adjacent thereto.

BRIEF DESCRIPTION OF THE DRAWINGS

[0160] These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein:

[0161] FIG. 1 is a schematic view showing a novel fleet protection attack craft formed in accordance with the present invention;


[0162] FIGS. 2-9 are schematic views showing further construction details of the novel attack craft shown in FIG. 1, including further details of its command module, buoyant tubular foils (BTFs) and struts;


[0163] FIGS. 10-15 are schematic views showing further details of the BTFs and struts, and the internal components thereof;

[0164] FIGS. 15A and 15B are schematic views showing how a gaseous envelope may be provided around the BTFs so as to reduce drag as the vessel moves through the water;
[0165] FIGS. 16-26 are schematic views showing further details of spoilers used to steer the novel attack craft and adjust its attitude;


[0166] FIGS. 27-36 are schematic views showing how the position of the struts and BTFs can be adjusted relative to the command module;

[0167] FIG. 37 is a cross-sectional view of a buoyant tubular foil having air channels therein and having air trap fins on portions of its periphery, and further shows preferred configurations of air trap fins;


[0168] FIG. 37A is similar to FIG. 37, but showing a substantially complete array of air trap fins mounted on the tubular foil;

[0169] FIGS. 37B and 37C are side elevational views of a buoyant tubular foil having air trap fins thereon and extending onto a strut fixed to the tubular foil;


[0170] FIG. 37D is a cross-sectional view of a buoyant tubular foil having air channels therein;

[0171] FIG. 38 is a schematic view of a marine vessel having a propeller system comprising a single propeller; and


[0172] FIG. 39 is a schematic view of a single buoyant tubular foil in the form of a torpedo.


DETAILED DESCRIPTION OF THE INVENTION

Overview

[0173] Looking first at FIGS. 1-6, there is shown a novel fleet protection attack craft 5. The attack craft 5 generally comprises a command module 100 for carrying a crew, weapons and payload (including passengers), a pair of buoyant tubular foils (BTFs) 200 for providing buoyancy, propulsion and steering, and a pair of struts 300 for supporting command module 100 on BTFs 200.

[0174] As seen in FIGS. 4, 7 and 8, and as will hereinafter be discussed in further detail, struts 300 can be disposed in a variety of different positions vis-à-vis the command module 100, so that the attack craft 5 can assume a number of different configurations, depending on the desired mode of operation, whereby to provide high speed, extreme stability, and stealth capability.

[0175] Thus, for example, in standard seas, attack craft 5 may be placed in the configuration shown in FIG. 4 (i.e., so that the struts 300 are disposed approximately 45 degrees off the horizon, and at approximately a right angle to one another) so that command module 100 is safely out of the water and the vessel has modest radar, infrared and visual signatures.

[0176] However, in high seas, while operating at high speed, attack craft 5 can be placed in the configuration shown in FIG. 7 (i.e., so that the struts 300 are disposed substantially perpendicular to the horizon, and substantially parallel to one another) so that the command module 100 stands well out of the water and is free from the affect of swells.

[0177] Furthermore, depending on sea conditions, the attack craft 5 can be in a configuration somewhere between those shown in FIGS. 4 and 7.

[0178] Attack craft 5 is also designed to operate in stealth mode, by lowering its physical profile. In this case, the attack craft 5 can be placed in the configuration shown in FIG. 8 (i.e., so that struts 300 are disposed almost parallel to the horizon, and almost co-linear with one another) so that the command module 100 is disposed just above, or actually in, the water, reducing its radar, infrared and visual signatures. This mode can be very useful when the attack craft 5 is being used for reconnaissance purposes and/or to deliver small teams of special forces behind enemy lines and/or to extract the same.

[0179] Thus, in one preferred form of the invention, the attack craft 5 is normally operated in the configuration shown in FIG. 4, with the command module 100 completely out of the water, but the command module being as low as possible so as to have a reduced profile. However, in high seas and at high speed, the attack craft 5 may be operated in the configuration shown in FIG. 7, so that the command module 100 stands well clear of any swells. And, when desired, the attack craft 5 can be operated in the configuration shown in FIG. 8 so as to assume a stealth mode.

[0180] Or, attack craft 5 can be operated in a selected configuration between those shown in FIGS. 4, 7 and 8.

Prior Art Designs for Achieving High Speed and/or Extreme Stability

[0181] There are currently two competing approaches for achieving high speed and/or high stability in a water craft. These are (i) the hydrofoil approach, which generally provides high speed; and (ii) the Small Waterplane Area Twin Hull (SWATH) approach, which generally provides high stability.

The Hydrofoil Approach

[0182] Hydrofoils have been in experimental use for many years, and today are in active service around the world for a variety of applications. Hydrofoils generally employ small airplane-like wings ("lifting foils") which provide lift for the hull of the vessel. The lifting foils are typically lowered into the water while the vessel is underway. At higher speeds, the lifting foils are capable of lifting the hull of the vessel completely out of the water, thereby allowing the vessel to operate with only its lifting foils (and their supporting struts) in the water, whereby to minimize drag and increase vessel speed. However, the lifting foils themselves provide no buoyancy and therefore cannot support the vessel at slower speeds. Thus, the vessel can only operate in hydrofoil mode when moving at substantial speeds. In addition, due to the thin nature of the hydrofoil's lifting foils, it is not possible to house the vessel's engines within the lifting foils themselves-instead, it is necessary to house the engines within the hull of the vessel and to use transmission technologies (e.g., mechanical, hydraulic and/or electrical means) to transfer power from the vessel's engines down to its lifting foils, which carry the propellers. However, these power transmission technologies all involve substantial losses in power (thereby necessitating the use of larger engines and/or resulting in lower speeds) and significantly complicate the propulsion system of the vessel.

The SWATH Approach

[0183] SWATH vessels employ two or more torpedo-shaped structures which are disposed underwater and attached to the main body of the vessel with fixed vertical struts. The torpedo-shaped structures provide buoyancy for the main body of the vessel, which remains completely out of the water. In this way, SWATH vessels resemble catamarans, except that the two pontoon hulls of the catamaran are replaced by underwater torpedo-shaped structures which reside immediately below the hull at the ends of the vertical struts. The SWATH design generally provides excellent stability because the underwater torpedo-shaped structures are less affected by wave action than a traditional wave-riding hull. However, the substantial skin friction, and the inefficient hydromantic shape of the large underwater torpedo-shaped structures, generally result in higher power consumption. This higher power consumption in turn necessitates the use of larger engines and/or results in reduced vessel speed. However, the use of larger engines is itself problematic, since the engines must then be housed in the hull or, if the engines are to be housed in the underwater torpedo-shaped structures, the underwater torpedo-shaped structures must be enlarged. Housing the engines in the hull introduces all of the power transmission problems discussed above with respect to hydrofoils, inasmuch as the propellers are mounted to the underwater torpedo-shaped structures. Conversely, enlarging the underwater torpedo-shaped structures increases skin friction problems, and inefficient hydromantic shape problems, discussed above-which in turn necessitates the use of even larger engines. For this reason, it has previously been impossible to build a small, high-speed SWATH vessel. In addition to the foregoing, the SWATH design typically requires a high profile in order to ensure that the hull of the vessel remains completely out of water, particularly in high seas. This gives the SWATH vessel larger radar, infrared and visual signatures, thereby making it easy to detect and target.

Novel Approach for Achieving High Speed and Extreme Stability

[0184] The present invention overcomes the problems associated with the prior art through the provision and use of novel fleet protection attack craft 5. Attack craft 5 supports a command module 100 on a pair of buoyant tubular foils (BTFs) 200 via movable struts 300. BTFs 200 normally provide all of the buoyancy required for the craft, with command module 100 remaining completely out of the water. More particularly, BTFs 200 and struts 300 are often the only portions of the craft which contact the water, and they provide low friction hydromantic cross-sections so as to minimize water resistance. Significantly, BTFs 200 house substantially all of the propulsion, fuel and steering systems for the craft, thereby providing the craft with an unusually low center of gravity and permitting the volume of command module 100 to be dedicated to crew, weapons and payload. Furthermore, struts 300 are movable relative to command module 100, thereby permitting the craft to assume a number of different configurations. This unique approach results in a craft with unparalleled speed and stability regardless of sea conditions, and with lower radar, infrared and visual signatures, thereby making it difficult to detect and target. Various aspects of the craft will now be discussed in further detail.

Command Module 100

[0185] Referring to FIGS. 1-9, command module 100 generally comprises a watertight enclosure 105 (FIG. 3) having a hull-like bottom surface 110 (FIGS. 4, 5, 7 and 8). Command module 100 includes a cockpit 115 (FIGS. 2, 3, 6 and 8) for housing a pilot and weapons officer, and a bay 120 (FIG. 9) for housing weapons and payload (including passengers). Command module 100 further includes a rear hatch 125 (FIGS. 5, 6 and 9) for permitting entry and exit of crew, weapons and payload (including passengers), and a top hatch 130 (FIGS. 2, 6 and 9) for permitting various weapons systems to be raised out of the bay 120, fired, and then lowered back into the bay 120.

[0186] Command module 100 is armored to protect all occupants, weaponry and payload. Windscreens 135 (FIGS. 7 and 9) are formed of bullet-resistant materials.

[0187] Command module 100 comprises watertight bulkhead enclosures which, combined with hull-like bottom surface 110, allow waves to wash over the command module without effect when the attack craft 5 is operating in its stealth mode (see below). Automatic vent doors seal any open systems against water leakage when attack craft 5 is in the stealth mode.

[0188] The outer structure of the command module 100 is preferably based on so-called "stealth" principals in order to minimize the radar signature of the craft. More particularly, the outer surface of the command module 100 is designed to deflect radar energy and return only a minimal amount of radar energy to the radar transmitter. To this end, the exterior surfaces of command module 100 are preferably highly angular, with the angles being selected so as to reflect the radar energy either downward towards the water or upward into the sky. In any case, the exterior surfaces of the command module 100 minimize the amount of radar energy reflected directly back to the sender. Furthermore, the command module 100 preferably incorporates a radar-absorbent paint which is capable of absorbing or further reducing any incident radar energy.

[0189] Command module 100 is also configured to house all of the control systems for piloting the attack craft, all of the weapons control systems for operating the weapons carried by the attack craft, an auxiliary generator for supplemental power requirements (e.g., for navigation), a battery charger, an air filtration system, a head, a sink, an air compressor, etc.

[0190] The weapons systems carried by attack craft 5 preferably comprise (i) one 20 mm Vulcan Gatling gun, equipped with optic and night vision; (ii) two 30 caliber Miniguns equipped with optic and night vision; (iii) one or more 2.5 inch laser-guided rockets; and (iv) 8 "mini" torpedoes. Preferably, the Gatling gun, Miniguns and rockets are housed within bay 120 for elevated deployment through the top hatch 130, and the "mini" torpedoes are mounted to the exterior of the command module 100, e.g., such as is shown at 140.

Buoyant Tubular Foils (BTFs) 200

[0191] Referring next to FIGS. 10-15, a pair of the buoyant tubular foils (BTFs) 200 provide buoyancy, propulsion and steering for the attack craft 5. Each of the BTFs 200 generally comprises a hollow tubular structure 205 which houses an engine 210 for powering a propeller system 215, a fuel tank 220 for supplying fuel to engine 210, and steering elements (or spoilers) 225 for steering the attack craft 5.

Hollow Tubular Structure 205

[0192] Hollow tubular structure 205 generally comprises a hollow hull which provides buoyancy for the attack craft 5. Hollow tubular structure 205 is configured to provide stability at low speed operations while still providing low water friction and an improved hydromantic profile to enable speeds of over eighty knots. At high speeds, the configuration of the hollow tubular structure 205 provides extraordinary stability for the vessel, due to the flow of water over the elongated tubular structure 205.

[0193] More particularly, the low friction hydromantic cross-section of hollow tubular structure 205 traverses water with the lowest possible skin friction forces and the best hydromantic shape obtainable, yet still houses the engine 210 and the fuel tank 220, and supports the propeller system 215 and steering elements 225. It has been determined that best performance is achieved where the hollow tubular structure 205 has a cross-section which is between about 1/10 and about 1/30 of the length of hollow tubular structure 205, and preferably about 1/20 of the length of the hollow tubular structure. By way of example, but not limitation, excellent performance can be achieved when the hollow tubular structure 205 has a 3 foot outer diameter and a 60 foot length.

[0194] As seen in FIGS. 12-15, the hollow tubular structure 205 comprises a plurality of disconnectable sections that permit easy access to components disposed within the interior of the hollow tubular structure 205, e.g., for maintenance and quick replacement of power and sensor modules. By way of example, but not limitation, the hollow tubular structure 205 can comprise a center section 230 which is mounted to a strut 300, a forward section 235 which is dismountable from the center section 230, and a rear section 240 which is dismountable from the center section 230. Preferably, interior components are equipped with slides for easy entry into, and removal from, the hollow tubular structure 205. By way of example, but not limitation, FIG. 14 shows how the engine 210 may be equipped with slides 245 for supporting the engine 210 within the hollow tubular section 205, and to facilitate insertion into, and removal from, the hollow tubular structure 205.

[0195] The forward section 235 and the rear section 240 can mount to the center section 230 in a variety of ways. By way of example, but not limitation, the sections can be mechanically held together (e.g., by hydraulics, power screw actions, etc.) or they can twist lock together (e.g., in the manner of a bayonet-type mount). A watertight seal is provided between the sections so as to ensure hull integrity. The seal can be a continuous circular shape to match the cross-section of the hollow tubular structure 205, e.g., a resilient O-ring having a round or flat cross-section. Alternatively, the O-ring can be an inflatable seal (e.g., like the inner tube of a bicycle tire) that can provide adjustable sealing forces by the injection of an appropriate amount of fluid (e.g., gas or liquid). Preferably, each O-ring seal has two sealing surfaces, i.e., the face surface between adjacent sections and the face surface against the skin of the hollow tubular structure 205.

[0196] The ability to quickly unlock the various sections of the hollow tubular structure 205 permits the rapid servicing and/or replacement of the various components contained within the hollow tubular structure 205, e.g., engine 210, fuel tank 220, etc.

Gas Turbine (Jet) Engine Propulsion

[0197] The engine 210 can be a conventional diesel engine, internal combustion engine, rotary engine, electric motor, etc. Preferably, however, the engine 210 comprises a gas turbine (jet) engine, e.g., of the sort used in aircraft, and particularly of the sort used in helicopters. A gas turbine engine is preferred due to its high power, small size and low weight. More particularly, a gas turbine engine typically has a horsepower-to-weight ratio of about 2.5 horsepower (HP) per pound. By comparison, a modern marine diesel engine typically has a horsepower-to-weight ratio of about 0.5 HP per pound. Inasmuch as there is generally a direct correlation between vessel acceleration and weight, it is generally desirable to use a high power, low weight engine in a high speed craft. Thus, a gas turbine engine is the preferred propulsion unit for the attack craft 5.

[0198] Significantly, a gas turbine engine is also ideal for use in the attack craft 5 inasmuch as its size and configuration are perfectly suited for disposition within the hollow tubular structure 205. More particularly, gas turbine engines typically have an elongated, somewhat cylindrical configuration which easily fits within a hollow tubular structure. Significantly, gas turbine engines generally have relatively modest cross-sections, such that the gas turbine engines fit within a relatively small diameter tube. By way of example, but not limitation, the T53L13 gas turbine (jet) engine manufactured by Lycoming Engines (a division of Avco Corporation, a wholly owned subsidiary of Textron, Inc.) of Williamsport, Pa. has a diameter which is ideally suited for disposition within the hollow tubular structure 205 of the attack craft 5.

[0199] The use of a gas turbine engine in BTFs 200 also provides significant additional advantages.

[0200] First, the use of a gas turbine engine in each BTF 200 easily allows for the use of a centerline drive shaft to transfer power to the propeller system 215. This is an enormous advantage when it comes to efficiently delivering large amounts of power to the propeller system 215.

[0201] Second, a gas turbine engine provides a starter generator that performs two functions, i.e., (i) to start the turbine engine, and (ii) to generate DC power. More particularly, most gas turbine engines provide 24 volts DC at 300 amps. This allows the attack craft 5 to power all of its electrical systems from the gas turbine engines, with the need for only a small supplemental generator for charging batteries.

[0202] In addition, placing a gas turbine engine inside the hollow tubular structure 205, which is underwater, also provides superior cooling for the gas turbine engine since the radiated engine heat is transferred to the surrounding water through the skin of the hollow tubular structure 205.

[0203] Furthermore, gas turbine engines are generally designed to be quickly and easily removed (e.g., by sliding) from an aircraft fuselage. Similarly, the gas turbine engine can be quickly and easily removed (e.g., by sliding) from the hollow tubular structure 205.

[0204] The gas turbine engine usually has a high internal rpm (greater than 19,000 rpm) with internal gear reductions. Preferably, a gearbox 250 using planetary gears connects the engine 210 to the propeller system 215. This approach provides a gearbox which is smaller than the outside diameter of the gas turbine engine.

Gas Turbine (Jet) Engine Intake And Exhaust

[0205] The "Achilles heel" of a gas turbine engine is its need to rapidly intake large quantities of fresh air and to rapidly expel large quantities of exhaust air. As a result of this need to rapidly move large quantities of air in and out of the gas turbine engine, gas turbine engines have not heretofore been a candidate for use in underwater structures (e.g., submarines and the submerged portions of SWATH vessels) due to the inability to adequately aspirate the jet engines.

[0206] A critical aspect of the attack craft 5 is the air intake and exhaust systems which support the use of gas turbine engines underwater. In this respect, it will be appreciated that the design of the air intake and exhaust systems is complicated by the fact that attack craft 5 is designed to change configurations (e.g., as shown in FIGS. 4, 7 and 8) and the air intake and exhaust systems must be able to accommodate these configuration changes. More particularly, in attack craft 5, the gas turbine engines are housed underwater in BTFs 200, the BTFs 200 are disposed at the ends of struts 300, and struts 300 are movable relative to command module 100 (see FIGS. 4, 7 and 8). Thus, the air intake and exhaust systems of the attack craft 5 must be capable of rapidly moving large quantities of air in and out of the gas turbine engines, and through the struts 300, while at the same time accommodating movement of the struts 300 relative to the command module 100.

[0207] To this end, the attack craft 5 comprises an air intake and exhaust system for rapidly delivering large quantities of fresh air to the gas turbine engine 210 and for rapidly expelling large quantities of exhaust air from the gas turbine engine 210. The air intake and exhaust system generally comprises an engine intake duct 255 and an engine exhaust duct 260. The intake side of the engine intake duct 255 is disposed in the command module 100 so that it can access cool air, which increases the efficiency of the gas turbine engines 210. Preferably, the intake side of the engine intake duct 255 is funneled so as to generate ram air forces while the attack craft 5 is moving at speed, which further increases the efficiency of the gas turbine engines 210. The outlet side of the engine exhaust duct 260 is disposed in the command module 100 so as to provide efficient exhaust venting with a minimal heat signature. Engine intake duct 255 and engine exhaust duct 260 preferably pass through a flexible coupling located at a junction of the strut and the command module, in order to accommodate movement of the strut vis-à-vis the command module. This flexible coupling also accommodates other lines passing from the command module 100 to the BTFs 200 via the struts 300, e.g., fuel re-fill lines, electrical power lines, electrical control lines, etc.

[0208] It should be appreciated that the flexible coupling is configured so as to allow engine intake and engine exhaust to be vectored and bent while still accommodating the large gas volumes associated with the gas turbine engine. Furthermore, the flexible coupling is designed to accommodate high exhaust temperatures created by the gas turbine engine. The use of heat-resistant flexible materials in the coupling is essential to allow movement of the struts relative to the command module.

[0209] It should also be appreciated that moving large quantities of air through a narrow strut (which is thinner than BTF 200) entails using substantially the entire inner structure of the strut as an air intake duct and an engine exhaust duct. In one preferred form of the invention, the engine exhaust duct 260 is routed inside the air intake duct 255 so as to allow the exhaust to be cooled by the intake air, whereby to provide a lower thermal signature for the attack craft 5. In another preferred form of the invention, the engine exhaust duct 260 is not routed inside air intake duct 255-rather, in this form of the invention, engine exhaust duct 260 is separate from the air intake duct 255, and the exhaust in engine exhaust duct 260 is separately cooled, e.g., with a water cooling jacket. Furthermore, in this form of the invention, insulation may be used to keep the cool air in the air intake duct 255 from being heated by the hot exhaust in the engine exhaust duct 260 in order to increase the efficiency of the gas turbine engines 210.

[0210] Preferably, the engine exhaust duct 260 includes insulation to prevent heat of the gas turbine engine 210 from overheating the outer skin of the strut 300.

[0211] In one form of the present invention, the engine exhaust ducts 260 are double-walled, so as to allow a fluid to be circulated around the inner hot duct, whereby to further cool the engine exhaust and provide a lower thermal signature.

Attack Craft Propulsion Using Battery Power

[0212] Preferably, the attack craft 5 also includes an electric motor (not shown) and batteries (not shown) for selectively driving the propeller system 215. More particularly, in certain circumstances (e.g., reconnaissance operations and the delivery and/or extraction of special forces) it may be desirable to operate with reduced noise. In these circumstances, the electric motor and batteries may be used in place of the gas turbine (jet) engine discussed above.

Propeller System 215

[0213] Most vessels in use today utilize propellers which are disposed at the stern of the vessel and push the vessel through the water. This approach is generally satisfactory for most vessels. However, stern-mounted, pushing propellers are generally not satisfactory for those vessels which are trying to achieve very high speeds, e.g., speeds in excess of 80 knots. This is because propellers located at the stern of the vessel engage water which has been agitated by the prior passage of the vessel through the water. Since the efficiency of propellers is highly affected by the state of the water the propellers move through, stern-mounted, pushing propellers are generally impractical for high speed craft.

[0214] Some high speed boats in use today (e.g., hydroplanes and ocean racing boats) use stern-mounted, surface-penetrating, forward-facing propellers that ride partially submerged in agitated water with air mixed in. These piercing propellers are designed with a heavy trailing edge and anti-cavitation cupping. These piercing propellers withstand the extreme forces of high horsepower and high rpm because the propeller is never fully engaged in the water.

[0215] However, this type of propeller would not be effective for the attack craft 5, since with BTF 200, the propeller system 215 must be fully submerged.

[0216] Significantly, the present invention utilizes a propeller system 215 which comprises a pair of forward-facing, pulling, counter-rotating propellers 265, 270 located at the bow end of each BTF 200.

[0217] More particularly, a propeller system 215 is placed at the bow of each BTF 200 so that the forward-facing, pulling propellers can "bite" into virgin water, whereby to obtain maximum efficiency. Furthermore, each propeller system 215 comprises two propellers, a leading propeller 265 and a trailing propeller 270, operated in a timed, counter-rotating mode, so as to provide reduced cavitation for the forward propeller. Leading propeller 265 is the main propulsion element and does the majority of the work of pulling of the vessel. Trailing propeller 270 spins in the opposite direction from the leading propeller and evacuates water from behind the leading propeller, thereby permitting the leading propeller to work with maximum efficiency. Thus, trailing propeller 270 moves water out from behind leading propeller 265 so that the leading propeller can pull more water in. This provides increased propeller efficiency, which translates into higher speed and lower fuel consumption.

[0218] Using the serially-mounted, counter-rotating propellers 265, 270 also permits smaller propeller diameters to be used. This is because the surface areas of the two propellers combine to provide an overall effective surface area which is equivalent to the surface area of a single, larger diameter propeller. However, it is difficult to rotate a large diameter propeller at high speeds due to the forces involved. Thus, the use of serially-mounted, counter-rotating propellers permits the propellers to be rotated at higher rpms, thereby permitting higher speeds to be achieved.

[0219] In addition to the foregoing, by using two counter-rotating propellers, there is no side torque. More particularly, side torque in propellers is the result of the centrifugal forces created by the rotation of the propeller. This side torque creates a tendency for the vessel to turn in the direction of the rotation of the blade. Side torque is not desired with attack craft 5, since it involves a loss of energy and can create steering issues for the vessel.

[0220] The gearbox 250 connects the gas turbine engine 210 to the propeller system 215. More particularly, the gearbox 250 is configured to convert the single rotational motion of the output shaft of the gas turbine engine 210 into the dual, co-axial, counter-rotational motions needed to drive the counter-rotating propellers, 265, 270.

Super-Cavitation

[0221] By placing the counter-rotating propellers 265, 270 on the forward end of BTFs 200, the propellers are able to pull the vessel through clean, undisturbed, virgin water, thereby ensuring optimal propeller performance. In addition, by placing the two serially-mounted, counter-rotating propellers on the fount end of BTFs 200, attack craft 5 is able to generate a highly gaseous environment, comprising a jet stream of dense collapsing bubbles that encapsulate BTFs 200 and significantly reduce vessel drag. More particularly, the actions of the propellers 265, 270, working together, pull water through the leading propeller 265 and allow the trailing propeller 270 to heavily cavitate the rapidly moving water and create a heavy stream of gaseous bubbles which surround the outer surfaces of BTFs 200. This gaseous envelope reduces hull drag and greatly increases the speed of the vessel, since the BTFs are essentially "flying through bubbles". See FIG. 15A. In this respect it should be appreciated that the kinetic coefficient of friction with air is approximately 1/800th the kinetic coefficient of friction of water. Furthermore, the faster the vessel goes, the greater the reduction in hull friction, inasmuch as (i) a greater quantity of gaseous bubbles are created by the serially-mounted, counter-rotating propellers, and (ii) the bubbles do not have time to collapse before BTFs 200 have passed completely through them.

[0222] Attack craft 5 can also include additional means for producing an encompassing gaseous envelope. More particularly, a plurality of small holes 275 (FIG. 15B) are preferably located immediately behind trailing propeller 270 and disposed in a circler fashion about the periphery of the BTF structure. The holes 275 are in communication with ductwork leading to the outside air, allowing the trailing propeller to create a siphon effect, drawing air down for release just aft of the trailing propeller, whereby to create an even more dense gaseous envelope for reducing BTF friction. Alternatively, a pressurized gas source connected to the small holes 275 can also be used to release gas immediately aft of the trailing propeller, whereby to create the desired gaseous envelope for reducing BTF friction.

[0223] In yet another form of the invention, a supply of friction-reducing fluid (e.g., detergent) can be connected to the aforementioned small holes 275, whereby to create the desired friction-reducing envelope about BTFs 200.

Rudderless System

[0224] Conventional rudders are continuously deployed in the water, so that they create friction and drag not only when being manipulated so as to change the direction of the vessel, but also under normal operating conditions. This friction and drag has a substantial detrimental effect on the speed of the vessel.

[0225] In contrast, and looking now at FIGS. 16-26, attack craft 5 provides forward and aft steering elements (or spoilers) 225 that are projectable from, and retractable into, the outer skin of hollow tubular structure 205. In this respect it should be appreciated that each of the spoilers 225 can be projected an adjustable amount outboard from hollow tubular structure 205. Furthermore, command module 100 can be provided with various control systems which permit each of the spoilers 225 to be operated in a coordinated fashion or, if desired, independently from one another.

[0226] In one preferred form of the invention, sixteen spoilers 225 are provided: four spoilers 225 at the front of each BTF 200 and four spoilers 225 at the rear of each BTF 200, with spoilers 225 being disposed at the "12 o'clock", "3 o'clock", "6 o'clock", and "9 o'clock" positions. This arrangement allows spoilers 225 to apply left, right, up and/or down forces (or any combination thereof) to the front and/or rear of each of the BTFs 200 while attack craft 5 is underway.

[0227] Spoilers 225 provide numerous significant advantages over conventional rudders.

[0228] For one thing, spoilers 225 provide substantially no drag when the vessel is underway and no directional changes are needed-this is because the spoilers then reside flush with the outer skins of the hollow tubular structures 205. Spoilers 225 impose drag on the vessel only when they are extended outwardly from the skins of the hollow tubular structures 205, whereby to provide the forces necessary to maneuver the vessel-and they are thereafter returned to their inboard (i.e., flush, and no-drag) positions as soon as the maneuver is completed and the vessel returns to standard forward motion.

[0229] Additionally, and significantly, the provision of the spoilers 225 on the fore and aft portions of hollow tubular structures 205 permits the application of more dramatic turning forces. More particularly, by setting a fore spoiler to turn in one direction and a corresponding aft spoiler to turn in the opposite direction, significant turning forces can be quickly and easily applied to the vessel using spoilers of relatively modest size. Thus, course corrections can be effected quickly, making the vessel extremely agile, while permitting the turning friction of the spoilers to be applied only for short durations.

[0230] Spoilers 225 can be used for turning left or right (see FIGS. 16-19), for adjusting the trim (i.e., the up/down attitude) of the vessel (see FIGS. 20-23), and/or to enhance deceleration of the vessel (see FIGS. 24-26).

[0231] Spoilers 225 can be flush plates that protrude from the outer skins of the hollow tubular structures 205 and cause friction when needed to change direction. Alternatively, the spoilers 225 can be made of an elastomeric material that can be inflated with air, fluids, etc. and which protrude from the outer skins of the hollow tubular structures 205.

Fuel Tanks 220

[0232] Fuel tanks 220 are housed inside BTFs 200, preferably in the center section 230. Fuel tanks 220 preferably comprise double-walled tanks made of a flexible bladder material (e.g., a flexible bladder disposed inside another flexible bladder). This arrangement allows for a fluid (e.g., seawater) to be pumped into the outer bladder in order to compensate for the consumption of fuel from within the inside bladder, thereby ensuring that the buoyancy of the attack craft remains constant.

Center of Gravity

[0233] The center of gravity for the attack craft 5 is intended to be as low as possible, in order to maximize vessel stability. This is achieved by positioning heavy components such as the engines 210 and the fuel tanks 220 within the BTFs, thereby lowering the vessel's center of gravity so as to be as close as possible to the midline of the BTFs. In this respect, it will be appreciated that turbine engines 210 and fuel tanks 220 constitute approximately [2/3] of the total vessel weight and, due to the construction of the attack craft 5, this weight is disposed entirely below the waterline. This leads to enhanced vessel stability.

Connecting Struts 300

[0234] As noted above, the connecting struts 300 attach BTFs 200 to the command module 100. As also noted above, the struts 300 are designed to be fixed to the BTFs 200 and pivot on the command module 100 to allow attack craft 5 to assume different configurations (FIGS. 4, 7 and 8), whereby to permit the command module 100 to sit different distances from the water. As seen in FIGS. 27-36, the struts 300 comprise hydraulic or electric jack screws 305 connected to load arms located within struts 300, whereby to move struts 300 relative to command module 100. In this respect, it will be appreciated that FIGS. 27-29 show struts 300 in a position corresponding to the attack craft configuration shown in FIG. 4. FIGS. 30-32 show the struts 300 in a position corresponding to the attack craft configuration shown in FIG. 7, and FIGS. 33-36 show struts 300 in a position corresponding to the attack craft configuration shown in FIG. 8.

[0235] Since struts 300 extend into the water, it is important to keep the struts as thin as possible so as to minimize drag.

[0236] It should also be appreciated that the structural integrity of the struts 300 relies primarily on the strength of the load arms located within the struts acting in conjunction with the outer skin of the struts, while using minimal internal frames. This is important, since the struts 300 need to have large areas of uninterrupted volume in order to permit engine intake to pass uninterrupted through the interior of the struts.

Fly-by-Wire Controls

[0237] In one preferred form of the invention, sensors are located on the hull-like bottom surface 110 of the command module 100 and continuously measure the distance of the command module from the water surface. A computer automatically adjusts the disposition of the struts 300 so as to maintain the command module a desired distance above the water surface. In this respect, it will be appreciated that, particularly when the attack craft 5 is operating at high speeds (e.g., 80 knots) in open water, it is important to keep the command module 100 from coming into contact with the surface of the water (and particularly important to keep the command module 100 from coming into contact with the irregular sea swells commonly found in the open sea).

[0238] Thus, for example, in standard seas, the attack craft 5 can be placed in the configuration shown in FIG. 4, so that the command module 100 is safely out of the water and the vessel has modest radar, infrared and visual signatures.

[0239] However, in high seas, while operating at high speed, the attack craft 5 can be placed in the configuration shown in FIG. 7 so that the command module 100 stands well out of the water and is free from the affect of swells.

[0240] Furthermore, depending on sea conditions, the attack craft 5 could be in a configuration somewhere between those shown in FIGS. 4 and 7.

[0241] Attack craft 5 is also designed to operate in stealth mode, by lowering its physical profile. In this case, the attack craft 5 can be placed in the configuration shown in FIG. 8, so that the command module 100 sits just above, or actually in, the water, reducing its radar, infrared and visual signatures. This mode can be very useful when the attack craft 5 is being used for reconnaissance purposes and/or to deliver small teams of special forces behind enemy lines and/or to extract the same.

[0242] Thus, in one preferred form of the invention, the attack craft 5 is normally operated in the configuration shown in FIG. 4, with the command module 100 completely out of the water, but the command module being as low as possible so as to have a reduced profile. However, in high seas and at high speed, the attack craft 5 may be operated in the configuration shown in FIG. 7, so that the command module 100 stands well clear of any swells. And, when desired, the attack craft 5 can be operated in the configuration shown in FIG. 8 so as to assume a stealth mode.

[0243] Or, the attack craft 5 can be operated in a configuration somewhere between those shown in FIGS. 4, 7 and 8.

[0244] Preferably, speed sensors feed speed data to a main computer, which adjusts the sensitivity of the steering controls so that, while travelling at low speeds, the controls are more reactive and when travelling at high speeds, the controls are less reactive. In other words, the main computer preferably adjusts the sensitivity of the steering controls so that (i) large movements of the steering controls (e.g., a joystick) are required at high speeds to make modest changes in the disposition of the spoilers 225, and (ii) small movements of the steering controls are required at slow speeds to make significant changes in the disposition of the spoilers 225. This construction eliminates the possibility that a modest movement of the controls at high speed will result in a catastrophic change in the direction or attitude of the craft.

Extendable BTF Boom

[0245] If desired, BTFs 200 can be provided with an extendible boom. This boom is deployable from the after end of the BTF, and is preferably flexible. The extendible boom can serve two purposes.

[0246] First, the extendible boom can have controllable surface protrusions along its length that can be enlarged or contracted so as to allow drag to be applied to the boom, thus further stabilizing the BTF in a manner similar to the tail of a kite. The protrusions cause drag that stabilizes the vessel in both the horizontal and vertical planes. The protrusions can be controlled by elastic bladders which are inflated so as to increase size (and hence drag) as desired, or a mechanical device located at the end of the boom that provides mechanical drag resistance, thereby increasing stability.

[0247] Second, the extendible boom can also house sonar, listening devices, magnetometers, gravity interruption sensors, etc. that can be used for the identification of submerged objects. By mounting these devices on the end of an extendible boom, the devices can be isolated from the remainder of attack craft 5, so as to minimize interference with device function.

Super-Cavitating Air Channels: "Air Trap Fins"

[0248] As described above, the present invention comprises a high speed SWATH boat with pontoon-type underwater hull friction reduction. Creating an air skirt around the hull of the buoyant tubular foil (i.e., by propeller-generated supercavitation and by injecting air through the hull and into the flow of water) displaces water from around the hull, allowing air to come into contact with the hull. Water has 800 to 1000 times more friction than air, so the air skirt dramatically reduces friction as the hull moves.

[0249] It is advantageous to keep the air bubbles traveling horizontally along the hull as much as possible, so as to decrease surface friction. Ideally, air needs to be maintained about the hull so as to act like a cushion and friction reduction means. At 50 knots, a 60 foot long structure passes through the bubble region in one second, so it is important to keep the air against the hull-even a 1/10 second increase in bubble life results in substantial friction reduction for the buoyant tubular foil. The following are various ways to do this:

[0250] 1. The hull is provided with many air outlet holes 310 located horizontally along the tubular foil 200, providing a plurality of horizontal air outlet channels.

[0251] 2. The hull is provided with long horizontal air trap fins 315 that allow air to be channeled along the length of the hull and not allow all the air to immediately escape outwardly and off the hull.

[0252] 3. The air trap fins 315 may be contoured (FIG. 37) so as to force the air bubbles to follow a tortuous path to escape from the hull.

[0253] 4. The air trap fins 315 may be disposed in a spiral around the hull in a helical manner, e.g., like a screw (FIG. 37), so as to allow air to be trapped and constrained against the hull as the air bubbles defuse along the channel.

[0254] 5. The air trap fins 315 may be of a scallop-type design (FIG. 37), providing air channels adjacent the hull of the buoyant tubular foil.

[0255] 6. The air trap fins 315 provide a water flow boundary around the circumference of the underwater hull (FIGS. 37B and 37C), providing a decrease in water density around the boundary water layer, from dense water to an air and water mixture. The height of the mechanical air trap fins 315 determines the water density boundary layer. The height of the fins 315 can be proportionally adjusted depending on the length of the hull.

[0256] 7. The air trap fins 315 run for a portion or an entirety of the length of the hull and may be radially distributed on all surfaces (FIGS. 37B and 37C).

[0257] 8. The air trap fins 315 may be radially distributed, except for the [1/4] to [1/2] bottom section of the underside of the hull (FIGS. 37 and 37D), in order to allow the bottom of the hull to ride on dense water and the remaining hull surfaces to be in an air/water bubbles stream. This provides better stability for the craft, due to the lack of compressibility of dense water supporting the craft.

Single Propeller Cavitation

[0258] In an alternative embodiment shown in FIG. 38, the marine vessel propeller system comprises a single propeller 530 placed at the bow of a buoyant tubular foil 500. The propeller 530 is sized and configured such that in operation the propeller creates and dispenses rearwardly a stream of supercavitated water which envelopes the marine vessel, which preferably is provided with air trap fins, as previously described, and operative to prevent immediate escape of the supercavitated water from the foil 500. Again, steering may be provided by spoilers as previously disclosed herein or, alternatively, rudders as shown in FIG. 38.

Submarine or Torpedo Embodiment

[0259] In the foregoing disclosure, there is disclosed a novel fleet protection attack craft 5 which generally comprises a command module 100 for carrying crew, weapons and payload (including passengers), a pair of buoyant tubular foils (BTFs) 200 for providing buoyancy, propulsion and steering, and a pair of struts 300 for supporting command module 100 on BTFs 200.

[0260] It is further within the scope of the invention to provide a novel submersible water craft, such as a submarine and/or a torpedo and/or an unmanned drone, which utilizes a single buoyant tubular foil, generally of the sort disclosed above, as the body of the submersible water craft (e.g., submarine, torpedo, unmanned drone, etc.).

[0261] In one form of the invention, and referring to FIG. 39, a single buoyant tubular foil, such as a body 500 of a torpedo, may be provided with a warhead 510 (e.g., detonator and high explosives) and provides for buoyancy (including negative buoyancy where desired), propulsion and steering 515, as is known in the art. More particularly, in this form of the invention, buoyancy is preferably provided by ballast tanks 520 contained within the body 500 of the torpedo. Propulsion is provided by at least one front-pulling propeller 530 of the sort disclosed above, and an electric motor contained within the body 500 of the torpedo, with the front-pulling propeller or propellers 530 providing an air skirt (supercavitation) around the body 500 of the torpedo during movement of the torpedo through water, in the manner previously disclosed. Again, steering may be provided by spoilers as previously disclosed herein or, alternatively, rudders as shown in FIG. 39.

Front Pulling Propeller Mechanism

[0262] It should be appreciated that with the preferred form of the present invention, a front pulling propeller mechanism is used to both (i) pull the buoyant tubular foil (BTF) though the water, and (ii) generate the friction-reducing air curtain which engulfs the trailing BTF. Thus, the same element (i.e., the front pulling propeller mechanism) is used to simultaneously provide both propulsion and the supercavitating friction-reducing air curtain. As noted above, each of these aspects provides significant improvements in propulsion efficiencies, with (i) the front pulling propeller mechanism biting into virgin water, which enhances the propulsion action of the propeller mechanism, and (ii) the front pulling propeller mechanism providing the supercavitating friction-reducing air curtain which reduces hull friction as the BTF moves through the water. Uniquely, the front pulling propeller mechanism is used to simultaneously provide both of these functions.

[0263] Significantly, the same approach is used regardless of whether the BTF is part of a SWATH surface vessel, or the BTF is the hull of a submarine or other submersible vessel, or the BTF is the fuselage of another form of submersible vehicle such as a torpedo or unmanned drone. In other words, with the preferred form of the present invention, the front pulling propeller mechanism simultaneously provides its dual function (i.e., propulsion and the supercavitating friction reducing air curtain) for the elongated hull structure (i.e., the BTF) which trails the front pulling propeller mechanism. In this way, the elongated hull structure is moved through the water with great efficiency and hence significantly increased speed.

[0264] It will be appreciated that it is important that the front pulling propeller mechanism be configured (e.g., blade shape, blade size, number of blades employed, counterrotation of the blades if more than one blade is provided, etc.) and operated (e.g., blade rotation speed, etc.) for both efficient propulsion and efficient air curtain generation. In this latter respect, it will be appreciated that the propeller mechanism should generate an air curtain of sufficient size and volume to engulf all (or substantially all) of the perimeter of the trailing hull structure (i.e., the BTF). In this respect it will be appreciated that not all front pulling propeller mechanisms will generate the supercavitating friction-reducing air curtain desired in the present invention. By way of example but not limitation, a propeller rotating relatively slowly will generate minimal supercavitation function (which may be a desired design feature, such as on a ballistic missile submarine which may give a priority to noise reduction). By way of further example but not limitation, a relatively small propeller may throw off a bubble stream, but the bubble stream may not be large enough to engulf the perimeter of the trailing hull structure and provide the desired air curtain about the outer surface of the trailing hull structure. Thus it will be appreciated that attention must be paid to the configuration of the front pulling propeller mechanism (e.g., blade shape, blade size, number of blades employed, counterrotation of the blades if more than one blade is provided, etc.) and to the operation of the front pulling propeller mechanism (e.g., blade rotation speed, etc.) in order to provide the desired supercavitating friction-reducing air curtain for the trailing hull structure. Appropriate design and operational parameters will be apparent to those skilled in the art in view of the present disclosure.

[0265] In one preferred form of the invention, the front pulling propeller mechanism comprises a pair of counterrotating propellers to efficiently provide both propulsion and the supercavitating friction-reducing air curtain, with the propellers having a diameter which is approximately X percent of the diameter of the trailing BTF, and a rotation speed of approximately Y revolutions per minute (rpm).

Non-Military and Civilian Applications

[0266] In the foregoing description, the attack craft 5 is described in the context of its use for military applications. However, it should be appreciated that the craft 5 may also be used for other, non-military applications, such as security applications (e.g., police, immigration and drug enforcement purposes), public safety applications (e.g., sea rescues), high-speed servicing and re-supply applications (e.g., for servicing oil drilling platforms), high-speed water taxi applications, private pleasure craft applications, etc.

Modifications of the Preferred Embodiments

[0267] It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.

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