Interesting.
Does algae attach to rust? Joe?

Scotty

"jlrogers±³©" wrote in message
m...
http://www.wired.com/news/technology...,66833,00.html
A new environmentally friendly coating based on sharks' skin may
soon help
the U.S. Navy increase ship speeds while saving fuel.

The coating doesn't go anywhere near the engines -- it will be
applied on
the hull of ships below the waterline, where all manner of algae,
barnacles
and other wee beasties attach themselves, slowing ships and reducing
their
maneuverability.

"Aircraft carriers can't get up enough speed to launch their planes
if
there's too much marine growth on their hulls," says Anthony
Brennan, a
University of Florida professor of materials science and engineering
and the
lead developer of the shark-inspired coating.
Putting an aircraft carrier into dry dock to clean the hull is
expensive and
time-consuming, said Brennan. Water inlets for nuclear-powered ships
and
submarines are also constantly getting plugged up with algae,
barnacles and
other matter.

"Navy ships spend the majority of their time in harbors, and that's
when
marine growth can really build up," he said.

Of the $550 million to $600 million the Navy spends annually on
powering its
ships and submarines, at least $50 million stems directly from drag
due to
marine growth fouling the vessels' hulls, said Stephen McElvany, an
environmental quality program officer in the Office of Naval
Research's
physical science division.

Existing antifouling paints such as tributyltin, or TBT, kill algae
and
barnacles when they latch on. TBT is being banned worldwide by the
International Maritime Organization, or IMO, the U.N. body
responsible for
overseeing shipping-related issues.

TBT has caused deformations in oysters and sex changes in snails,
according
to Susan Sang, a wildlife toxicologist for the World Wildlife Fund
in
Canada. The chemical also accumulates in fish, sea birds and marine
mammals,
damaging reproductive and immune systems, Sang said.

Although military vessels are exempt from the IMO ban, the Navy
stopped
using TBT many years ago in favor of copper-based paints that also
kill
organisms that latch on.

"Copper-based paints are less harmful than TBT, but are still
toxic," said
Sang.

The Navy is funding research at the University of Florida in hopes
of
obtaining a nontoxic coating that will reduce routine cleaning of
fouled
ships, McElvany said. Currently, every one or two years divers
operate
specially designed scrubbing machines and clean ships while they're
in the
water.

"It's a costly operation," McElvany said.

To find a way to persuade algae to move on rather than killing them,
Brennan
and colleagues turned to nature. Sharks don't have algae or barnacle
problems despite being underwater all their lives. Shark skin is
made up of
tiny rectangular scales topped with even smaller spines or bristles.
This
makes shark skin rough to the touch. This irregular surface makes it
difficult for plant spores to get a good grip and grow into algae or
other
plants.

"It's like trying to walk across a bed of nails when some nails are
longer
and unevenly distributed," Brennan said.

Using a combination plastic-and-rubber coating, Brennan replicated a
version
of shark skin that is made up of billions of tiny raised,
diamond-shaped
patterns, visible under a microscope. Each "sharklet" diamond
measures 15
microns, or 15 thousandths of a millimeter, and contains seven
raised ribs
that resemble different lengths of raised horizontal bars.

In lab tests, the coating -- provisionally named Gator Sharkote --
reduced
by 85 percent the settlement of spores from a very common and
detrimental
type of algae called Ulva, a green seaweed often seen on the sides
of ships.

"The only place the spores land right now is where we have a defect
in the
pattern," Brennan said.

The coating makes use of the fact that algae spores actually check
out a
surface before gluing themselves on. McElvany calls the coating
"kind of
magical" because the spores don't like the pattern and move on.

But one pattern might not be good enough for all types of marine
growth.

"Marine plant spores are unbelievably adaptive and will change their
shape
to attach on to surfaces," said Brennan.

Sharks cope with this easily enough because their scales move and
flex as
they swim. In research recently patented, Brennan and his colleagues
have
made the diamond-shaped pattern dynamic, or changeable, under the
influence
of a low-power electric current.

The ribs on the surfaces swell and shrink, in effect flexing in and
out from
the hull surface as the current varies. That may also be useful
because the
movement could prevent the accumulation of silt and other debris on
the
hulls, which is often a precursor to plant and barnacle growth, he
said.

The new, dynamic version of Gator Sharkote is currently being put to
the
test against critters found in oceans off Florida, England, Hawaii,
California and Australia. Coating Navy vessels with some version of
Gator
Sharkote is still many years away, said McElvany, but the results
from the
basic research so far have been "pretty amazing."

There may also be important biomedical applications, Brennan said.
Testing
has shown that the dynamic version of the coating impedes the
attachment and
growth of animal cells, which may make it useful on medical implants
such as
catheters and heart valves. Currently, cell and tissue growth on
these
implants often reduces or impedes their function.

"Our whole concept is a surface design that we can tailor to the
application, whether in the ocean or human body," Brennan said.


jlrogers±³©
Beaten by George W. Bush! Now that's funny!