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Few creatures spawn more fear than sharks. But these complex fish also have provided inspiration for several useful technologies. One new idea has captured the interest of the U.S. Navy.
Shark skin has been used by many cultures as sandpaper. It's kept shipmates safe in slippery-when-wet conditions. Swimsuits modeled on shark skin are said by Speedo to reduce drag by up to 4 percent.
Now, research by two separate groups could lead to synthetic shark skin that would make ships and submarines faster and less expensive to operate.
If the research pans out, submarines -- already stealthy and shark-like -- could become even more so.
The problem
The growth of barnacles, mussels, algae and other organisms adds to fuel costs for the military and shipping industry, increasing drag by up to 15 percent, scientists say. In the industry, it's called bio-fouling.
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The Navy spends about $600 million each year to power ships and submarines. At least $50 million of that cost is directly related to bio-fouling, says Navy scientist Stephen McElvany.
Paints laced with deadly biocides curb the problem, but they are also toxic to other marine life.
Some fish, and also whales, are fouled by hitchhiking marine life. But not sharks. Scientists have figured out that the secret to clean sharks is in the complex design of their scales.
Amazing scales
Shark scales are made of a hard material called dentin. Basically, the scales are tiny teeth. They all point backward, so a shark would feel smooth if you dared to stroke it from head to tail, but rough if you ran your hand the other way.
Studies have found that the scales act as armor for a shark and also create tiny vortices that reduce drag to make them faster. The scales also allow sharks to swim silently compared to other fish that generate considerable noise when they ply the water.
The design has proved useful to humans in many ways.
Norwegians applied real shark skin to the soles of their boots to prevent slippage on wet ship decks. In the 2000 Olympics, swimmers began wearing full-body suits modeled on shark skin.
What's good for the shark ...
Importantly, shark scales flex individually, constantly changing and limiting the amount of exposed surface area on which organisms can attach, scientists have learned.
Ralph Liedert of the University of Applied Sciences in Bremen, Germany has developed a synthetic shark skin of elastic silicone that similarly reduces the contact surface, making it harder for barnacles to gain a foothold.
While simpler in design than shark scales, the ship skin reduced bio-fouling by 67 percent in tests, Liedert will report this week at the Society for Experimental Biology's annual meeting in Barcelona.
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Mussels and barnacles make some of the strongest adhesives known (other scientists try to mimic the properties to make better household glue). But the glue of a barnacle, Liedert found, can only penetrate so far into a rough surface, explaining why the scales prevent them from sticking.
With the fake skin applied, a ship moving at 4-5 knots becomes self-cleaning, removing most organisms, Liedert found.
Military interest
In separate work funded in part by the U.S. Navy, scientists at the University of Florida have developed a similar coating, made of tiny diamond-shaped scales that flex in and out to impede the growth of organisms.
The coating was tested in a lab using a common algae. The algae's spores had a very hard time attaching to the surface.
"It normally sticks to everything, but we have reduced spore settlement by 85 percent," said Anthony Brennan, a University of Florida professor of materials science. "The only place the spores land right now is where we have a defect in the pattern."
While the high-tech skins could reduce costs for the shipping industry, they could prove a strategic advantage for the military.
McElvany called the finding “exciting" but said there are still challenging research hurdles to clear before the technology could be deployed.
"If achieved, this improved coating could not only be exempt from future environmental constraints and regulations, it would also provide increased fuel efficiency and velocity of Navy vessels," McElvany said
http://www.livescience.com/technology/050715_shark_skin.html
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