Scientists disprove claims that olympians’ swimsuits reduce drag thanks to shark skin-mimicking technology
A lot of fanfare was made at the 2008 Beijing Olympics, when Micheal Phelps swam his way into the record books by winning 8 gold medals for the United States. The swimsuit company Speedo was especially vocal about the part they had played in his victories. They were responsible for Phelp’s “state-of-the-art” swimsuit, which, they claimed mimicked the drag-reducing roughness of shark skin, thus giving him the competitive edge. Speedo might not be able to make such claims anymore, however, because a new study, published in the Journal of Experimental Biology, demonstrates that the performance enhancing abilities of these swimsuits are nowhere near comparable to that of shark skin.
Dr. Johannes Oeffner and Dr. George V. Lauder from Harvard University used a flapping foil robotic device to determine the self-propelled swimming speed (SPS), a measure of performance, of real shark skin from two shark species, a silicone riblet material mimicking shark denticles, and the Speedo “shark skin-like” swimsuit fabric, Speedo® Fastkin FSII. They also used sanded down shark skin, devoid of denticles, the tooth-like scales found in the skin’s surface, to serve as the control treatment.
The researchers used an environmental scanning electron microscope, a microscope that uses beams of electrons, to take high-resolution images of the materials. The pictures revealed that the “shark skin-like” Speedo material followed the usual template for swimsuit fabric, with parallel seams going along it, albeit with slightly more pronounced seams.
They then filmed high-speed video sequences to analyze the materials’ performance in water and to observe how particles of water flow around the materials’ surfaces. They also recorded the swimming behavior of a one and half-year-old spiny dogfish (Squalus acanthias).
The researchers found that, despite claims to the contrary, the Speedo swimsuit fabric did not increase the swimming speed of the robot. The shark skin, on the other hand, increased its swimming speed by 12.3%, and the silicone improved its swimming speed by 7.2%.
Dr. Lauder is quick to point out that these results do not necessarily indicate that Speedo has been scamming its wearers. He believes that they do increase swimming performance, but not for the reasons we think. “Swimmers who wear these suits are squeezed into them extremely tightly, so that are very streamlined. They’re so tight that this could actually change your circulation, and increase the venous return to the body, and they are tailored to make it easier to maintain proper posture even when tired.”
Previous studies had looked at shark skin performance on a rigid model but not on a flexible one, missing the importance of skin deformation in drag reduction. In those cases, the denticles were thought to slow down sharks. When the researchers in this study used a flexible robot and compared shark skin to sanded down shark skin, they found that the denticle-free skin was considerably slower. The scientists conclude that shark denticles not only reduce drag, but also increase thrust, a completely novel idea.
Biomimicry, a design philosophy that attempts to apply nature’s principles to everyday products, is an incredibly exciting field that has brought us many interesting and innovative new ideas, like mimicking wing scales in butterflies in order to scatter light. A problem does arise, however, when companies use biomimetics to justify charging enormous amounts of money for products that don’t perform the way they should, a practice to which Mother Nature would undoubtedly object.
Oeffner, J., & Lauder, G. (2012). The hydrodynamic function of shark skin and two biomimetic applications Journal of Experimental Biology, 215 (5), 785-795 DOI: 10.1242/jeb.063040