Navy Fishing for Sub Design Ideas

The tiny boxfish looks like a cartoon character with its peculiar shoe-box shape and bright yellow body with black spots. It lives in a rigid shell, unable to bend its body because its scales are fused together.

It seems an unlikely candidate for military research, but this tiny wonder is the very model the U.S. Navy hopes to use to design a new miniature submarine that will scour the ocean bottom, operating efficiently even in turbulent waters.

The sub could have myriad uses, whether to comb for underwater mines, conduct scientific research or hunt for wreckage from airplane crashes.

“Fish are phenomenally maneuverable compared to anything that is man-made,” said Jeff Walker, a biology professor at the University of Southern Maine who is studying the boxfish to better understand how it swims and moves its body.

“It’s a lofty goal for a human-made vehicle to achieve the performance of a fish.”

The Office of Naval Research awarded Walker a three-year, $90,000 grant to work with a team of engineers on the project. The Naval Undersea Warfare Center in Newport, R.I., will be in charge of designing the sub, also known as an “autonomous underwater vehicle,” or AUV.

The AUV should be able to remain stable while working in waters shallower than 1,000 meters, said Robert Gisiner, who is overseeing the project at the Office of Naval Research. Existing AUVs, he said, are not good at handling underwater currents greater than 1 knot.

“What we’re interested in creating is an underwater [machine] that has the abilities of a biological organism that you can’t get in standard structures now,” Gisiner said.

The boxfish is related to the better-known puffer fish and lives primarily in tropical waters around coral reefs in the Pacific Ocean.

Working in a cramped laboratory at the University of Southern Maine, Walker is studying three juvenile boxfish that he has named King Kong, Nessie and Jaws. A high-speed digital camera records their activities and downloads the images onto a computer, where the movements and speed can be precisely measured.

The boxfish is no bigger than a couple of matchboxes stacked one on top of the other. But it is a perfect research specimen because it is so maneuverable and can turn on a dime, almost like it is rotating on an axis.

Boxfish fins look like folding fans and act as paddles. By paddling one of its pectoral fins forward and the other backward, the fish can make a 360-degree turn with barely any movement--just like a person in a stationary rowboat paddling the oars in different directions to turn around.

“The turning radius of this fish is essentially zero,” Walker said.

Walker is chronicling the fish’s exact turning radius and the speed at which it turns around. Later, he will determine the usefulness of the fins on the top and bottom of its body. After all, there would be no need to include top and bottom fins on an underwater vehicle if they serve no useful function.

He will also place the fish in a wave tank and determine how it acts in turbulent waters.

Walker isn’t the first scientist to study fish locomotion to further the design of unmanned submarines. “RoboTuna” is an underwater vehicle whose tail is designed after the tail of a bluefin tuna. “Robo-Bass” has fins on its side that are modeled after the fins of a small-mouthed bass.

Nobody has given a name to the machine that will be built based on the boxfish. Whatever the result, Walker’s work illustrates the relationship between biology and engineering.

“It’s an odd connection between biologists and engineers,” Walker said. “But I think it’s a fruitful one.”