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Scientists Discover Why Sharks Can Swim So Fast

Posted by timothy on from the goosebumps-might-help-evade-them dept.

MediaSight writes "Shortfin mako sharks can shoot through the ocean at up to 50 miles per hour (80 kilometres an hour). Now a trick that helps them to reach such speeds has been discovered — the sharks can raise their scales to create tiny wells across the surface of their skin, reducing drag like the dimples on a golf ball."

2 of 103 comments (clear)

  1. This has been known for many years by Anonymous Coward · · Score: 5, Interesting

    Back in the 80s we switched from polishing the bottom of our race boat to a glass like finish to spraying it with a gel mixture (as in gel coat, not jello) full of small oblong granules. We found that by spraying it a certain way we could get the particles to more or less line up in the orientation we needed. Careful polishing after the fact gave us the finish we were looking for without destroying this new, textured surface. We did this directly in response to an article I had read about how a sharks skin allows it to move quickly through the water. The article went further to say that this also applied to most all scaled fish.

    This modification allowed the boat to break the surface tension of the water more easily when launching from a standing start and added several miles an hour to our top end speed. In a game where every mile an hour might cost 1000s or 10s of thousands of dollars this was *the* most effective modification we had ever done to the boat and one that to this day we joke about because it took our competition many years to figure out.

  2. WTF?? - Ah! by IcyHando'Death · · Score: 5, Interesting

    I was dubious about this science when I read the article, but I learned something in the end.
    From the article:

    The team created artificial shark skin with a 16 x 24 array of synthetic scales, each 2 centimetres in length and angled at 90 to the surface of the "skin".
    They then placed the arrangement in a stream of water travelling at a steady 20 centimetres per second.

    Shark scales are tiny - the crown is barely visible to the naked eye. So these scientists have scaled them up (so to speak) at least 2 orders of magnitude. With fluid dynamics the scale of a model can change everything, especially in the range of sizes they are working with here. I thought they should have substituted a more viscous fluid for the water in order to get a useful model. I thought maybe this was just preliminary work and they'd do a better study if their results suggested that it could be valuable."

    But before flaming the Slashdot editors for trumpeting this study as a "discovery", I did a little Googling and quickly wound up at Wikepedia learning about Reynolds numbers. Turns out you can model turbulence pretty accurately as long as the Reynolds number stays the same. In this case the Reynolds number is proportional to both the size of the shark scales and the velocity of the water flow, so it can be preserved while the scales are made larger if the velocity is reduced proportionally.

    Which is exactly what they did. They're studying sharks swimming at 80 km/hr.

    80km/hr = 8,000,000 / 3600 cm/sec = 2200 cm/sec

    Or, about 100 times faster than the flow rate they used in their model. Neat.