Sharkskin: Small Ridges Create Huge Efficiency

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For decades, engineers have been concerned with movement efficiency based on the shape and smoothness of an object. The conventional rule was the smoother an object was, the more efficiently it would move through a fluid. Within the past 10-15 years or so, that has been starting to change. Sharkskin holds the secret to creating greater hydrodynamic and efficient machines.

While the sharks shape is amazingly hydrodynamic, its skin is anything but smooth. The well known "sandpaper" texture of sharkskin is created by many small scales called dermal denticle which translates to  "small skin teeth." These scales are adorned with longitudinal grooves which reduces drag and results in water moving more efficiently over their surface. Why would this make them more efficient?

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As water flows over smooth surfaces fast moving water begins to break into turbulent vortices. The water flowing towards the surface of the object is moving slower than the water that is flowing further away. When these different velocity fluids mix, they create the vortices which slow down the object. The grooves in the sharks scales channel the water and pull some of the faster moving water to mix with the slower. The result is less speed discrepancy between the waters and thus less turbulence.

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This principle has been most famously used for Speedo's Fastskin suits which has strategically placed bumps and ridges which behave like the sharks scales and boasted a 3% improvement in speed. During the 2000 Olympics, 80% of medal winners wore the suit and 13 of the 15 swimming records broken where by athletes outfitted with it. The suit proved so efficient that it was later banned after the 2008 Olympics because it became viewed as a form of "technological doping" and did not allow the competition to be determined by the athletes performance.

 The technology has also been applied to the hulls of ships and the blades of wind turbines. The hulls of ships and the blades of turbines are surface coated emulates the physical characteristics of sharkskin. The coating allows for more efficient movement through their fluid environments, water and air respectively. The ships are able to travel greater distances using less energy, and the turbines will be able to create more energy from less wind.

Nest post, we will explore the marvelous antimicrobial property of sharkskin.