Scientists’ research targets ways keep ships barnacle free

By ERIK SLAVIN | STARS AND STRIPES Published: August 25, 2009

YOKOSUKA NAVAL BASE, Japan — While watching a Trident submarine pass through Pearl Harbor in 2002, Anthony Brennan came up with an idea that might one day help the Navy defeat its slimiest enemy.

Muck, barnacles and the multitudes of organisms that attach themselves to ship hulls aren’t just unsightly, they are expensive, too. The extra drag on ships costs the Navy about $1 billion annually in extra fuel and maintenance costs, according to the Office of Naval Research.

Brennan, a University of Florida engineering professor, compared the muck-laden submarine’s smooth, rotund shape to a whale — a creature whose surface readily attracts parasites and barnacles.

Then he thought of sharks, which have very few such freeloaders looking for a ride.

After years of ongoing research, Brennan says he is close to doing large-scale trials on Sharklet, an application that could effectively give a surface ship’s hull a sharkskin coating and prevent buildup without using toxic compounds.

Lab results on Sharklet-patterned surfaces have shown dramatically less organic growth when compared with smooth surfaces typically found on ship hulls.

"If this performs in [tests] in the ocean, there is no limit to the size of ship that it goes on," Brennan said.

The crucial changes to the surface aren’t visible to the naked eye. Brennan says he is trying to perfect the shark scale-like pattern at a size of 2 to 16 microns, which would prevent extremely small organisms from binding.

For comparison, a human hair’s diameter is about 50 microns and a shark’s actual scales are sometimes about 150 microns.

Besides the added efficiency that would come with reduced drag, the Sharklet design itself could possibly make ships more hydrodynamic, Brennan said.

Brennan’s work is one of multiple projects that receive funding from the Office of Naval Research’s program to prevent microorganism buildup.

When organisms form a more persistent biofilm, they can add 20 percent more drag to a ship, according to the research office. A plague of barnacles can push that figure up to more than 60 percent.

For surface ships, the Navy’s current solution is to use copper-based paint. The copper slowly leeches from the hull and kills the organisms trying to attach themselves.

However, it also kills other life in the ocean and taints the water with heavy metal pollution.

Regulatory pressure and anticipated restrictions on toxin-based paints are driving the Navy’s push for new hull coatings, said Linda Chrisey, biosciences and biocentric technology program officer with the ONR.

"Several candidates are in the process of being scaled up for large panel testing at open water sites using a variety of tests," Chrisey said.

Besides Brennan’s work, the research office has keyed in on University of Washington Professor Shaoyi Jiang’s research in testing mixed charges known as zwitterionic compounds. The compounds alternate between positive and negative charges to prevent organisms from attaching.

Because both Brennan’s and Jiang’s projects inhibit bacteria, they could also be used in medical and other applications outside their military uses, ONR officials said.

The research office is funding other projects aimed at stopping biofilm growth as well, Chrisey said.

Some of the technologies in development theoretically could be mixed and matched.

However, there is no set timeline; it will still be years before a new coating makes it to shipyards, Navy officials said.

An electron microscope captures the pattern of Sharklet, a surface technology patterned after a shark’s scales.

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