Sailing drone launched as high endurance submarine hunter
NATIONAL HARBOR, MD – The Navy could use one of the world’s oldest technologies to defeat one of the newest by launching autonomous sailing drones to find and track enemy submarines.
Saildrone markets its unmanned surface vessels – the company calls its vessels “unmanned” – fitted with a composite rigid-wing sail, as a persistent reconnaissance platform capable of carrying sophisticated sonar equipment. Drones, which power their keel-mounted payloads with solar power, can stay at sea for long periods of time to perform a range of missions, according to Brian Cannon, Saildrone’s vice president of ocean mapping.
“We use the wind to navigate them, mainly collecting ocean data, atmospheric and oceanographic observations, but we can also put a payload in the keel and do things like fishing surveys or single beam mapping.” Cannon told USNI NEWS in the Navy. The League’s 2021 annual Sea-Air-Space Symposium in National Harbor, Maryland, where Saildrone was on display for the first time.
“From a defense perspective, we use them to search for seamounts that could pose a danger to underwater navigation,” he said. “It’s a very inexpensive way to get out into an area where someone thought they saw something; we can go out and say if it’s there and stay clear or if it’s deep enough for a submarine to pass safely.
Any of the Saildrone models could carry passive acoustic sensors and transmit signals to a manned surface vessel, Cannon said. The larger versions can tow a sonar array or other underwater sensor to chase enemy submarines. It can also search near the surface or the surface of the water with hydrophone sensors or cameras to perform anti-drug missions, he said.
The company, headquartered in Alameda, Calif., Built 100 of the 23-foot Explorer drones. . Thirty of the ships actively ply the waves from the Arctic to the tropical Pacific Ocean, map the seabed, measure schools of fish, monitor shark mating behavior and conduct other data collection missions, said Cannon.
The fully electric unmanned sailboat sports solar panels on its sail and deck that charge its batteries and power the payloads. A small propeller is primarily used as an auxiliary power generator that spins while the boat sails, Cannon said. Explorer has endurance of up to a year at sea.
A teleoperator defines a corridor inside which the drone can navigate and draws waypoints. The on-board computers do the rest, in particular by optimizing the pace and controlling its orientation in relation to the waves.
“Usually it’s a predefined plan that they execute and if they deviate we will know,” he said.
The Coast Guard has already tested the feasibility of deploying autonomous sailboats for persistent maritime domain awareness in remote areas of the ocean.
In 2020, six of the 23-foot versions of the Saildrone left Hawaii for a month-long demonstration of their endurance. Several one-week tests presented operational scenarios, including general monitoring of surface traffic; detect illegal, unregulated and unreported (IUU) fishing; search and patrol; and port security. The drone fleet successfully provided information to Coast Guard units during testing without incident.
With the success of Explorer, Saildrone decided to “take the next step and ask what else we can do with these,” Cannon said. That brainstorming resulted in the 72-foot Surveyor, which had a 50-foot mast, an auxiliary diesel engine and “the same capacity as a survey vessel for ocean mapping,” he said.
Surveyor has keel-mounted sonar up to 7,000 meters and a shallow water multibeam echosounder that can collect very high resolution maps of shorelines. The motor is needed to boost solar power to run the power-hungry sonar, Cannon said. The motor can also be used for propulsion in calm wind but is mainly used to charge the on-board batteries.
Surveyor sailed from San Francisco to Hawaii in July and mapped the entire 28-day transit over a hitherto unexplored ocean.
“Only 20 percent of our oceans are mapped,” Cannon said. “We need a lot more of these vehicles that can go out and map those parts of the ocean that I don’t mean people don’t care about but aren’t a priority.”
Saildrone recently launched a 33ft prototype called Voyager which can do both shallow water bathymetry and maritime domain knowledge. Like its big cousin, Voyager will carry radar, an Automatic Identification System (AIS) transceiver and high-resolution 360-degree cameras. Cannon said the company over the past five years has captured 100 million images of the ocean’s surface and objects floating on it. In a previous RIMPAC exercise, drones were able to capture images, identify vessels and transmit that data via satellite, Cannon said.
The idea is “to be able to have another asset with your eyes on the water to patrol certain areas, so that the ships can go and do what the ships do best,” he said. “Same thing with ocean mapping… we’re not trying to replace ships. These ships are very expensive and having them come and go slowly, like mowing your lawn, to map the ocean is a very expensive way to do it when we can do it that way.