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To Battle Barnacles, Ships Test Fake Sharkskin

Brian Handwerk
for National Geographic News
July 22, 2005
 
Whether you're a ship or a shark, you need a sleek surface to speed through the sea. Which is why barnacles, algae, and other marine organisms that glom onto hulls or bodies are such pests.

To know what sailors are up against, consider this: Barnacles produce an epoxy-like cement that can stick to Teflon, not to mention hulls and rudders.

Such "biofouling" speeds corrosion and increases drag resistance, reducing speed and maneuverability—at a cost of billions of dollars a year to the maritime industry.

"Any surface that is submerged in seawater could be fouled," said Staffan Kjelleberg of the Centre for Marine Biofouling and Bioinnovation at the University of New South Wales in Sydney, Australia.

Shipwrights once covered wooden-hulled ships with lead, copper, and other metals to thwart biofouling. In more recent times, shipyards have typically painted hulls with toxic paints.

Today, such environmentally harmful products are facing tougher regulation, and scientists are hard at work searching for green alternatives.

Some researchers are seeking more environmentally friendly paints, which could employ chemicals or compounds found in marine plants naturally resistant to ocean pests.

Other scientists are exploring ways to develop marine surfaces inspired by Mother Nature.

Artificial Shark Skin

Antonia Kesel and Ralph Liedert, at the University of Applied Sciences in Bremen, Germany, has created an artificial sharkskin that mimics natural sharkskin's innate resistance to biofouling.

"All marine animals and plants need a reliable strategy against unwanted overgrowth by fouling organisms such as mussels, algae, and barnacles," Liedert said.

"Most fishes use either slimes, toxic substances, or regular skin-peeling as a way to get rid of parasites. However, sharks don't possess these kinds of mechanisms."

Instead, sharks have an outer layer of hard scales that flex against one another and rest on an underlying layer of elastic skin. The structure helps sharks swim efficiently and minimizes the area to which organisms can adhere.

Liedert's synthetic version mimics this composition with silicone, in hopes that the scale structure is what gives sharks their biofouling defense.

Research has "shown that barnacle cement is not capable of penetrating very deeply in the grooves between the microstructures of artificial shark skin," Liedert said. "Therefore, barnacles have only a very little effective contact surface on which they stick."

Liedert's most successful "skin" reduced barnacle settlement by 67 percent in North Sea tests. It also enabled ships to clean off any organisms that tentatively attached themselves, simply by traveling at speeds of just four to five knots (about five to six miles an hour).

Liedert presented his findings at the Society for Experimental Biology Annual Main Meeting in Barcelona, Spain.

Research on similar synthetic skins has been ongoing for years, but success has proven elusive.

"The solution to this problem has been hard to achieve," said Kjelleberg, of the University of New South Wales, "because surfaces submerged in seawater absorb the various chemicals, proteins, and organic material and themselves become modified."

Meanwhile, ecologically friendly paints have been difficult to develop, not to mention expensive.

Liedert reports that the cost of his artificial sharkskin is similar to that of commonly used antifouling paints, though a method of applying the skin to ship hulls remains a lingering technical hurdle.

"It's a bit more complicated than just to paint the ship in the conventional way," he said. "But we are working on a solution."

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