Unlike most other sea creatures, sea lions use their forelimbs instead of a tail for propulsion. They also leave virtually no wake as they travel through the water. With an eye towards applying this design to human technology, George Washington University professor of mechanical and aerospace engineering Megan Leftwich has developed a robotic sea lion flipper.

Leftwich and colleagues started by videotaping swimming sea lions at the Smithsonian's National Zoo. Then, on a frame-by-frame basis, they digitally plotted the relative positions of each flipper's shoulder, elbow and wrist joints as they went through their range of motion. What they discovered was that as the sea lions clap their flippers in towards their body, the trapped water shoots back in a jet, propelling the animals quickly and silently forward.

Based on the joint positions plotted from the video, the scientists proceeded to create an articulated robotic plastic arm (seen below) that moves in the same fashion as a sea lion flipper. Leftwich then performed a 3D scan of an actual flipper, and used it to 3D-print a silicone covering for that arm.

The "skin"-covered arm was subsequently subjected to flow diagnostic techniques to study the effects that skin wrinkles and hairs may have on drag, as well as to establish how much force is required to move such a flipper through the water.

Leftwich is now planning on testing the robotic flipper alongside actual sea lions, in an enclosure at the SLEWTHS (Science, Learning and Education With The Help of Sea Lions) teaching aquarium in California.

Ultimately, it is hoped that the research could lead to designs for stealthy and efficient roboflipper-propelled underwater vehicles.

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