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Skin reduces drag: shark

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Shortfin mako shark / Mark Conlin / LicensePD - Public Domain

The skin of sharks reduces drag by having a scales with longitudinal grooves.

“In 2011, Dr. George Lauder’s lab at Harvard took some Mako sharkskin they had bought at the local fish market and put it in a flow tank to test how much the dermal denticles on the skin reduced the friction drag on their flexible robotic foil. They wanted to know whether all those bumps on the shark really made a difference in speed, so they tested the flow of water over the skin of a rigid foil and of a flexible one; with the denticles and without. It turns out they really do matter, increasing self-propelled swimming speed (SPS) by an average of 12.3% in the flexible foil.” (Zygote Quarterly)

Read more about the reduced drag of shark skin in Zygote Quarterly:
While a shark’s coarse shape is famously hydrodynamic, shark skin is anything but smooth. The very small individual scales of shark skin, called dermal denticles ("little skin teeth"), are ribbed with longitudinal grooves which result in water moving more efficiently over their surface than it would were shark scales completely featureless. Over smooth surfaces, fast-moving water begins to break up into turbulent vortices, or eddies, in part because the water flowing at the surface of an object moves slower than water flowing further away from the object. This difference in water speed causes the faster water to get "tripped up" by the adjacent layer of slower water flowing around an object, just as upstream swirls form along riverbanks. The grooves in a shark’s scales simultaneously reduce eddy formation in a surprising number of ways: (1) the grooves reinforce the direction of flow by channeling it, (2) they speed up the slower water at the shark’s surface (as the same volume of water going through a narrower channel increases in speed), reducing the difference in speed of this surface flow and the water just beyond the shark’s surface, (3) conversely, they pull faster water towards the shark’s surface so that it mixes with the slower water, reducing this speed differential, and finally, (4) they divide up the sheet of water flowing over the shark’s surface so that any turbulence created results in smaller, rather than larger, vortices. (Courtesy of The Biomimicry Institute)
About the inspiring organism
Med_isurus_oxyrinchus_shortfinmako Mako shark

Learn more at
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Bioinspired products and application ideas

Application Ideas: Decrease fuel consumption in water craft, increase performance in swimsuits, reduce friction inside pipes.

Industrial Sector(s) interested in this strategy: Transportation, manufacturing


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