Barnacles. They may look innocuous when you see them on the undersides
of breaching whales, but they increase drag on the underside of a ship
significantly, reducing its speed by up to 10 percent and increasing
fuel consumption by up to 40 percent.
For the Navy, which spends a lot of time and fuel sailing ships, this is a problem. In fact, the Navy is forced to spend $1 billion a year on extra fuel and the cleaning of its ships.
So it’s developing an autonomous robot inspired by the grooming behavior of sea creatures (PDF), and it’s currently undergoing tests by the Office of Naval Research for deployment in 2015 across the U.S. Navy’s fleet. The robot, which is something like an underwater Roomba, is described as a “robotic hull biomimetic underwater grooming,” or Hull Bug.
In general, “fouling” of ships affects the world’s entire fleet of ships, and is a major drag– literally!–on the fuel efficiency of vessels of every size. Traditional approaches to keeping barnacles and other “biofilms,” or collections of living gunk, off ships and submarines involve toxic paints laced with large amounts of copper. Not only do these paints pollute the harbors where ships spend most of their time, they’re a headache to dispose of when dry-docked vessels are sandblasted every decade.
Hull Bug represents a completely different approach to keeping ships free of crud: It’s not terribly powerful, but the idea is that it would be so easy to use, it could be deployed almost continuously, to gently sweep biofilms and baby barnacles off the underside of a ship. (The alternative are less-frequent cleanings carried out by divers equipped with spinning brushes, an expensive and difficult proposition.)
Hull Bug is inspired by the “grooming” behavior common to just about every crustacean on the planet. Hermit crabs even have a special pair of legs devoted to just this purpose:
The Hull Bug is relatively small: it’s less than three feet long, weighs 50 pounds, and uses a simple bulldozer attachment to keep a hull clear of material. But its most clever features are how it navigates and adheres to the ship.
On the Hull Bug’s underside is a cavity with a spinning propeller that creates a “captured vortex” that generates negative pressure against any surface. It’s a way for Hull Bug to remain firmly attached to the underside of a ship that’s way more efficient to a traditional thruster, and it’s one of the reasons that Hull Bug can operate solely on batteries.
Hull Bug also has a fluorometer–it sees fluorescence–on its front surface which allows it to “see” the parts of a ship that it has yet to sweep. In this way, it can cover the entire surface of a hull in the same way your Roomba cleans your floor.
As of 2010, the Office of Naval Research renewed the contract of Hull Bug’s maker, Sea Robotics, for an additional three-year test run. If it can be perfected in that time, it could have application well beyond the Navy. “Basically any boat over 45 feet which is in the water all the time can benefit from this kind of technology,” said Don Darling, President of SeaRobotics.
Aside from the challenges of working in an underwater environment, scouring the bottom a hull is substantially more complicated then vacuuming your living room floor. Hull Bug must use onboard sensors and its own algorithms to “provide obstacle avoidance, path planning, and navigation capabilities.” Hull Bug is essentially a fully autonomous submersible that must also figure out how to efficiently traverse a complicated three dimensional environment consisting–the contours of a ship.