USA: Dolphin skin inspires research aimed at keeping hulls clear of marine freeloaders.14th Nov 2002 Story: www.newsday.com
Surprising new lessons in dolphin anatomy and polymer chemistry may be teaching researchers a thing or two about how to keep ship hulls free of tubeworms, barnacles and other aquatic freeloaders.
Dolphins are well known among anatomists for the extraordinary hydrodynamic properties that allow them to reach sustained swimming speeds of 20 mph or more. Now a chemist is taking her inspiration from another exceptional dolphin feature - its unique skin topology - to combat the underwater "biofouling" of ship hulls, long considered an aggravation by the Navy and the shipping industry alike.
Karen Wooley, a professor of organic and polymer chemistry at Washington University in St. Louis, said marine organisms normally lock into place on ship hulls or pier pilings through secreted protein adhesives. These glues operate on the nanoscale level, a sub-microscopic realm that affords them Lilliputian footholds.
Speaking to science writers last month at a Council for the Advancement of Science Writing conference hosted by Washington University, Wooley explained that her work focuses on understanding molecular-level interactions between biological systems and synthetic materials, whether harmful or beneficial. Her challenge for combatting biofouling, then, has been to devise a polymer on the proper scale to prevent adhesion by such marine organisms.
Neil Gallagher, a professor of naval architecture at Webb Institute in Glen Cove, pointed out in a phone interview that a biofouled ship can lose up to 10 percent of its power after four or five years from the additional drag. The aquatic annoyance not only requires the expenditure of increasing amounts of fuel just to maintain the same speed, but also can expose spots on the hull to corrosive seawater, further increasing the cost of ship maintenance.
Biofouling and related seawater corrosion can similarly damage the metal surfaces of more static structures such as buoys, piers, jetties, intake pipes and offshore oil platforms.
Gallagher said workers generally haul a ship out of the water every two years to remove accumulated marine life by sandblasting or spraying with a high-pressure water jet before they reapply a protective coating. Early sailors used lead, lime and arsenic in their attempts to protect ship hulls, until chemists developed more effective anti-fouling paints based on metals such as tin and copper.
These coatings slow down the process by poisoning attached organisms ranging from barnacles to algae, but studies have shown that the metals, especially tin, leach into the surrounding water and persist there, where they pollute the environment. Tin in particular has been blamed for poisoning other marine life such as oysters and dog whelks.
"You have a paradox here," Gallagher said. "You want to make the surface of the ship poisonous so that marine organisms won't attach to it. But by its very nature, it's toxic."
Reflecting this concern, the International Maritime Organization - a United Nations agency - has called for a worldwide ban on applying tin compounds such as tributyltin, or TBT, to ships by 2003 and for their complete removal by 2008. In the United States, the Environmental Protection Agency has forbidden boaters from applying tin-based anti-fouling paint to the hull of any vessel less than 25 meters in length, or 82 feet, unless its hull is aluminum.
The regulations have spurred a wholesale shift to copper-based paint instead, with an estimated yearly price tag of $600 to $1,000 to coat the hull of an average-sized 40-foot yacht, based on informal surveys of Long Island marina operators.
"Let's say if you have no paint on the bottom, and if it's in the peak of the summer when the water's warm, you can have the entire bottom covered with little barnacles in four weeks," said Peter Needham, vice president of the Coecles Harbor Marina on Shelter Island. "Then you've got a mess on your hands."