GAINESVILLE, Fla. --- University of Florida engineers have
developed an environmentally friendly coating for hulls of
ocean-going ships based on an unlikely source of inspiration: the
shark.
UF materials engineers tapped elements of sharks’ unique scales to
design the new coating,
which prevents the growth of a notoriously aggressive marine algae
and may also impede
barnacles, according to preliminary tests.
If more extensive testing and development bear out the results, the
shark-inspired coating
-- composed of tiny scale-like elements that can actually flex in
and out to impede growth
-- could replace conventional antifouling coatings. These coatings
prevent marine growth but
also leach poisonous copper into the ocean.
The copper paints are wonderful in terms of keeping the ship
surface clean, but they are
poisonous and they accumulate at substantial rates in harbors,”
threatening marine life,
said Anthony Brennan, a UF professor of materials science and
engineering and the lead
developer of the coating. By contrast, there are no toxins
associated with our surface.”
Brennan’s project is being sponsored by the U.S. Navy, the world’s
largest maritime ship
owner, which has contributed at least $750,000 to the effort so
far.
According to the Navy, algae and barnacles on hulls increase drag,
slowing ships and reducing
fuel efficiency. Of the $550 million to $600 million the Navy
spends annually on powering its
ships and submarines, at least $50 million stems directly from
fouling-related increased drag,
said Stephen McElvany, a program officer in environmental quality
in the Navy’s physical
science division. The Navy hopes to find both a more effective and
environmentally friendly
technology than the copper-based paints.
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.
Brennan realized that sharks remain largely free of plants and
barnacles despite spending
their entire lives submerged. That contrasts, for example, some
other large-bodied marine
species such as whales, which attract marine growth.
Sharks have placoid scales, which consist of a rectangular base
embedded in the skin with
tiny spines or bristles that poke up from the surface the reason a
shark’s skin feels rough
to the touch. Brennan decided to try mimicking that surface with an
artificial coating to see if
it would also have antifouling properties.
His first product: a combination plastic/rubber coating that a
microscope reveals is made of
billions of tiny raised diamond-shaped patterns. Each sharklet”
diamond measures 15
microns, or 15 thousandths of a millimeter, and contains seven
raised ribs that at close
examination resemble different lengths of raised horizontal bars.
Laboratory tests show that the coating prevents a very common and
detrimental type of
algae, called Ulva, from becoming established because the algae’s
spores have great
difficulty attaching to the diamond-shaped configuration.
It normally sticks to everything, but we have reduced spore
settlement by 85 percent,”
Brennan said. The only place the spores land right now is where we
have a defect in the
pattern.”
That’s a major advance, as the algae is a major problem for nuclear
submarines, carriers
and battleships because it accumulates on inlet ports used to cool
nuclear reactors. It can
severely inhibit the vessel’s ability to operate,” Brennan said.
McElvany called the finding exciting,” saying Brennan and
colleagues’ research is both
unique in their approach and exciting in terms of their efficacy”
in deterring the Ulva spores.
The big hurdles that remain are to develop textures, patterns or
chemistry on the surface
that will also inhibit the settlement of a wide variety of the main
marine foulers, such as
barnacles,” he said.
The UF team, which also includes UF research scientist Ron Baney
and numerous graduate
students, hopes to achieve that goal with its latest version of the
coating. 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 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.
Both the original and newer versions of the coatings are being
tested in
