Cargo ships are huge polluters—in 2015, as they traveled the ocean delivering everything from smartphones to bananas, they emitted more than 200 million metric tons of CO2, roughly as much as the entire country of Vietnam. Unlike cars, which can easily be replaced with electric versions, ships are harder to decarbonize. But a relatively simple intervention from a new type of underwater robot can help significantly shrink emissions.

The robot, called the HullSkater, addresses one problem—as a ship travels through the ocean, a “biofilm” of algae and other microorganisms attaches to the sides of the vessel. That seemingly small change means that the ship uses more energy to move. “As the layer gets thicker and thicker, you get more and more drag or friction against the water when the ship is sailing,” says Hans Peter Havdal, a general manager at the Sweden-based technology consulting company Semcon, which partnered with a marine coating company called Jotun to design the new robot. The robot has been tested on ships globally and is coming to market now.

[Image: Semcon]

When the ship stops at a port for loading, the remotely controlled robot can travel over the hull, cleaning it with a motorized brush. Previously, cleaning happened much less frequently. “In the past, you had to bring the ship to a dock for cleaning and potentially for repainting,” Havdal says. “If you carry the HullSkater on board, you can launch this cleaning device while you’re waiting for the ship to be loaded. You can maintain the hull, clean it, and hence reduce the fuel consumption.”

Over five years, a single ship using the robot will be able to cut 22,000 metric tons of CO2 emissions—12.5% of its total emissions. (For comparison, that quantity of emissions is equivalent to burning 24 million pounds of coal.) The technology has a side benefit of reducing the spread of invasive aquatic species from port to port.

As the shipping industry looks for other ways to reduce emissions—with an industry-wide goal to cut greenhouse gas emissions in half by 2050, and the industry leader Maersk pledging to completely eliminate them—it may turn to hydrogen-powered ships. One recent report that looked at routes across the Pacific found that almost all trips could run on hydrogen if 5% of cargo space was used to store hydrogen fuel, or if each ship made an additional stop to refuel. If the industry makes that change, the robot could be a useful way to make it possible to carry less hydrogen. “Even if you have hydrogen or electric power, you still want to be energy efficient,” says Havdal.

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