Freezing cold and ringed with treacherous ice, the Arctic isn’t exactly hospitable territory for boats.

As a result, maps of the Arctic seafloor aren’t as detailed as they should be.

But that didn’t keep four vessels from sailing from Alameda, Calif., into the Arctic on an ambitious mission to make more detailed seafloor maps.

The 23-foot-long “saildrones,” as they are known, lacked crews but were packed with instrumentation and the ability to collect data about the ocean. Powered by only the wind and sun, four of the autonomous vehicles successfully completed an 8,000-nautical-mile mapping mission between May and October for the National Oceanic and Atmospheric Administration.

The Northwest Passage connects the Atlantic and the Pacific via the Arctic Ocean along the northernmost part of North America. It’s long been sought as a shorter alternative shipping route between Asia, the United States and Europe. But as melting Arctic ice potentially opens the route, NOAA and others want to know more about the topography of the seafloor to help protect wildlife and keep ships safe.

Saildrone, which designed the autonomous vehicles, collaborated with NOAA survey partner TerraSond on the mission.

When covid-19 travel restrictions prevented the saildrones from launching from Unalaska, Alaska, the boat bots took off from San Francisco Bay instead. Managers tracked them 24/7 as they tooled up the Pacific Ocean, through the Aleutian Islands and the Bering Strait, and to the Canadian border.

Along the way, one drone’s sonar failed. The vessel was repurposed as a moving weather buoy instead.

The other vehicles used single-beam echo sounder technology to map the seafloor at 65 and 164 feet.

Partway through their mission, the team realized that subsistence hunting among the Indigenous communities of Alaska North Slope was beginning early and retooled their mission.

There were other challenges, such as concerns about the dwindling amount of sunlight in the far north. But the orange saildrones survived and are on their way back to California after making new contributions to seafloor mapping.