Harbor Wing Technologies of Seattle and Pearl Harbor, Hawaii, is about to start building a 50-foot autonomous oceangoing trimaran that the company hopes will carry a host of sensors for the U.S. Navy.

So far, Harbor Wing has received $7.3 million for research and development of its unmanned autonomous sailing vessels through congressional earmarks to annual defense budgets. The Navy has not signed on to the company’s plan, but two Navy research agencies and Space and Naval Warfare Command have expressed interest in the vessels, said Mark Ott, Harbor Wing’s vice president and boat designer.

The 50-foot-long trimarans, to be called X-3s, would be powered by wind, an innovative “hard wing airfoil sail” and photovoltaic cells. They would be commanded by a computer, steered by algorithms and guided by Global Positioning System satellites. In the company’s vision, these “autonomous unmanned surface vessels” would be able to operate at sea for months at a time. They would follow instructions programmed into their computer memories, or they could be sailed by remote control in much the same way UAVs are flown over Iraq and Afghanistan by pilots located in the U.S.

When equipped with optical and infrared cameras, radar, sonar and other sensors, the vessels could provide the Navy with a long-endurance, lower-cost alternative to fuel-guzzling powerboats, helicopters and fixed-wing aircraft now used for surveillance and reconnaissance, Ott said. Unmanned sailing vessels are ideal for missions that range from spotting drug runners to listening for submarines to fighting irregular warfare, he said. A scaled-down version — a 30-foot catamaran — completed sea trials off Hawaii in 2007. Now, Harbor Wing has completed designs and is preparing to build the first full-size X-3.

The Navy has experimented with unmanned vessels for decades. It developed unmanned minesweepers as early as the 1960s. More recently, the Navy has tested a variety of unmanned vessels for intelligence, surveillance and reconnaissance missions; coastal patrols; and port security. And it has considered using them against pirates.

In the Navy’s 2007 “Unmanned Surface Vessel Master Plan,” the service lists seven missions for crewless boats, including mine countermeasures, anti-submarine warfare, electronic warfare and maritime interdiction support. And while the master plan focuses mainly on unmanned engine-powered vessels, it states that unmanned sailing vessels might be “well-suited to particular niche requirements.” To detect drug runners, for example, a string of X-3s might be deployed in suspected trafficking areas to spot suspicious ships. They could beam video, infrared images, radar data and other intelligence back to U.S. command posts. Similar tactics could be used to counter piracy, Ott said.

Harbor Wing says X-3s might also be used to keep an eye on areas that have been cleared of mines to ensure that new mines are not planted. And they could be used for range control to ensure that ships, whales or other intruders have not wandered into target areas when missiles, torpedoes and guns are being fired.

Infrared and electro-optical cameras along with a radar and communications antennas would be mounted atop the X-3’s 60-foot mast. Live images and data would be transmitted to larger ships, aircraft or shore bases via line-of-sight radios or satellite uplinks, providing real-time intelligence, Ott said.

One reason for the trimaran design is to provide a highly stable platform for the cameras and other sensors, he said. The vessel would be 40 feet wide, and its sheer width would make it less susceptible to rolling with the waves. When driven by a 20- to 25-knot wind, an X-3 can accelerate to about 15 knots and then rise up on its hydrofoils. “You instantly double your speed on the foils,” Ott said. The X-3 is designed to reach about 30 knots. “You don’t want to operate it in that mode” as a matter of routine, he said. “But it can be useful if there is an emergency and you need to get somewhere quickly.”

Even when there is no wind, the X-3 will have electric motors powerful enough to drive the boat up onto its hydrofoils for short bursts, he said.