Researchers look for ways to keep sea life
from finding a home on Navy vessel hulls
By EDWARD LUNDQUIST, Special Correspondent
“A fully fouled hull can result in
nearly 40 percent increase in fuel
consumption to maintain design
speed,” said Arthur A. Webb, sec-
tion head of Marine and Industrial
Coatings Synthesis with the Center
for Corrosion Science and Engi-
neering at the Naval Research La-
boratory (NRL). “Any accumula-
tion results in increase in fuel con-
sumption. A general rule of thumb
is that every 10-micron increase in
hull roughness results in 0.5 per-
cent increase in propulsion needed
to maintain speed.”
That is why the Navy has been
very interested in different kinds of hull coatings that
Hull coatings must prevent corrosion and preserve
the integrity of the ship. Most Navy ships have a layer
of epoxy primer underneath to protect the metal hull,
then a coating of a copper-based paint that has anti-fouling attributes.
Some anti-fouling hull coatings, such as Tributyltin
(TBT), have “biocide” chemicals that are toxic to
marine life. They work well, but can damage or destroy
certain types of sea life.
While TBTs are no longer used in new construction,
they are not uncommon on merchant ships today. The
Navy never adopted TBT paints, but even ablative copper-based coatings that have been common on Navy
ships for more than 30 years can leach toxins into the
Webb said new NRL-developed solvent-free, rapid-curing resin system coatings are self-polishing, with a
variable polishing rate that can be tailored depending
on where and how the ship will be operating.
“If a ship operates in warmer waters, we can tailor
the polishing speed to match the desired performance
for that environment; and we can tailor the polishing
Cleaning ship hulls when in port requires divers, underwater hull-scrubbing systems or even a dry dock, and that can be time-consuming and expensive.
■ A fully fouled hull can result in a significant increase in fuel consumption to maintain design speed.
■ Researchers are exploring different kinds of hull coatings that
deter fouling by sea life.
■ The Navy wants a surface that is “sleek, durable, nontoxic,
corrosion-preventing, nonfouling and cost-effective.”
The U.S. Navy is putting out the “unwelcome” mat for barnacles and other marine organ- isms. By studying what barnacles, oysters, sea
worms, mussels, algae and other sea organisms like
and do not like, the Navy aims to create an inhospitable environment on ships’ hulls where the sea life
will not settle down.
The bottom of a ship in a harbor is a magnet for
such creatures. Before the mooring lines are secured,
all kinds of sea life are checking out the underwater
hull looking for a surface to homestead. And they are
always ready to move in and put down roots.
But they are not welcome because plants and organisms that grow on the bottom of a ship can cause all
kinds of problems. Some create hard shells that can
increase hull drag that requires more ship propulsive
fuel consumption. Even bacteria, larvae and microscopic plants create drag.
The Navy devotes considerable resources to cleaning hulls when in port, but this requires divers, underwater hull-scrubbing systems or even a dry dock, and
that can be time-consuming and expensive.
The service spends an estimated $5 million annually
cleaning the underwater hulls of Navy ships.