RoboClam may become the first 'smart' anchor

Razor clam (left) and the RoboClam may lead to new anchoring technologies. (Donna Coveney/MIT)

CAMBRIDGE - It isn't cute, like Japan's robot dog. Or endearingly domestic, like those roboticized vacuum cleaners that beetle around the living room in pursuit of household dirt.

But mariners, oil outfits, and the military have big hopes for an unlikely contraption called RoboClam under design at the Massachusetts Institute of Technology.

RoboClam is meant to become the first "smart" anchor, a major departure from the prosaic piece of nautical gear that hasn't changed much in centuries.

In appearance, the RoboClam prototype is a modest rectangle of hinged bronze and steel, about the size of a deck of playing cards. In function, however, the device mimics the considerable burrowing skills of a razor clam - a common mollusk with an uncommon twitchy style of locomotion that MIT researchers have replicated in the RoboClam design.

"We want to make an anchor that can dig itself down to the right position to hold the vessel securely - and then, just as critically, easily reposition or free itself," said Anette Hosoi, the professor of mechanical engineering overseeing development of the robot.

"Present-day anchors are basically just big clunky weights that you splash overboard and hope they lodge into the right spot," she said.

The present diminutive size of RoboClam is just for test purposes; eventually, its engineers predict, the faux bivalve will be built to scales suitable for securing deepwater craft.

The RoboClam effort has received funding from Bluefin Robotics Corp. - a Massachusetts company that makes unoccupied submersible vessels to monitor such things as ocean temperatures and currents - and Chevron, the oil giant with fleets of floating drill rigs. The military is also keenly interested in smart anchors, as well as undersea digging devices that could be used to mark and destroy mines.

Much of Hosoi's research centers on mechanical propulsion systems inspired by nature. Still, why use a clam as a model? The lowly bivalves are more associated with chowder or splashes of Tabasco than high technology.

"We started two years ago looking at all creatures that burrow into undersea strata," said Amos G. Winter, a graduate student who has performed much of the work making RoboClam reality. "Quahogs, crabs, seaworms . . . ."

Armed with a shellfish license and homemade clam rake, and bundled into a cumbersome pair of chest waders, Winter scoured tidal flats near Gloucester, studying the creatures that thrive in the fecund sand and mud.

Razor clams grabbed his attention - for their speed, sleek shape, and stubborn tenacity in holding fast when finally cornered in the muck.

On a measure of anchoring force, Winter said, "razor clams beat everything, including the best anchors, by a factor of 10."

The creature can move through hard-packed sand, or thick sediment, at a "blistering" speed 0.4 inches per second, he said, making the razor clam "the Ferrari of bivalves."

But the speed of the clams posed a mystery.

In lab tests, the MIT researchers were puzzled to find that real-life clams were burrowing at velocities that seemed physiologically impossible, seemingly requiring far more force to push through the sand than the animals could exert.

Flummoxed, Winter videotaped the 7-inch-long mollusks in a custom-built, window-sided box filled with water and soda-lime glass beads - to simulate sand.

He pondered the videos for days before making a surprise discovery - to move, razor clams literally change their surroundings from near-solid sand to near-liquid slurry. Moreover, they push up to go down.

The clam first wiggles a fleshy foot into the sand below and pushes its shelled body upward. This creates a tiny pocket of space under the shell, which sucks in both water and sand. At the same time, it clamps shut its shell with a pronounced twitch that creates more slick slurry, while pumping blood into the extended foot.

"The foot expands into a blood-swollen balloon on which the clam pulls itself down through [previously compacted] sand or sediment that has been turned into quicksand," Winter said in an interview among burbling fish tanks, hissing pneumatic devices, and vials of unnaturally bright liquids at MIT's Hatsopoulos Microfluids Laboratory. With that in mind, MIT researchers designed Roboclam to twitch its metal shell for an instant, a motion that turns the sand in its vicinity into fluid syrup through which it easily slides.

For now, RoboClam remains in the experimental stage, powered by compressed air and reliant on external piston drives for its twitches.

"It opens and closes, and moves up and down, like a real clam," said Hosoi, the engineering professor. "The next step is to design an internal power source" - probably a battery - "that will make it autonomous."

Colin Nickerson can be reached at Nickerson.colin@gmail.com.