Gray's Paradox
     In 1936 Gray brought to light a problem that had never occurred to scientists before. It had been well-known for centuries that dolphins exhibited extraordinary speed in the water. Accounts of these playful animals racing ships were available in the early 20th century (Kramer 1960). The question that Gray focused upon was how they could attain such speeds. With a rudimentary estimate of the physiological power of a dolphin Gray was able to arrive at the conclusion that this power was mathematically insufficient to achieve the speeds mariners had observed dolphins to reach (Bechert 2000). Hence the paradox. 
     New light was brought to the problem some 25 years later when Kramer (1960) hypothesized that compliance of dolphin skin would delay water flowing over the skin in becoming turbulent, thus dramatically reducing drag and solving Gray's Paradox.  Some 30 years after Kramer's hypothesis was proposed, several studies finally proved its underlying principles to be correct using methods unavailable in his time.  However, 
it was also found that Kramer's hypothesis really explains only a small fraction of Gray's Paradox. The major factor that accounts for dolphins swimming at "inexplicably" fast speeds is an error in Gray's calculation. By assuming dolphins to perform at the same physiological levels as humans, Gray made the paradox seem much greater than it truly is (Bechert 2000). Thus, given their power outputs, dolphins swim at more normal speeds than Gray calculated. 
     If you were wondering what this has to do with shark skin, please be patient.  While dolphin skin appears to have little drag reducing capabilities, another pelagic marine animal can apparently do great things with its skin.  Shark skin has been shown to have drag reducing properties that industry is only now beginning to take advantage of.

 

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