“Whenever we have done hull
material trade studies for our air
cushion vehicles, surface effect
ships and planing boats, we have
almost always ended up with welded aluminum,” Moore said. “It does
require more care in design and
manufacture, but it provides the
best balance between performance,
cost, durability and maintainability
for our class of high-performance
marine craft.”
Composites
At the Huntington Ingalls Industries
(HII) Composite Center of Excellence in Gulfport, Miss., very large
composite structures are taking
shape. According to Jay Jenkins, the
HII site director at Gulfport, the
deckhouse and hangar for the DDG
1000 has been fabricated in
Mississippi and is being shipped to
General Dynamics Bath Iron Works
in Maine to be mated with the hull
of the future USS Zumwalt.
With composite structures, less
topside weight improves stability
and has speed and fuel efficiency
benefits, and it does not fatigue and
will not crack or corrode.
“Life-cycle costs are dramatically less,” Jenkins said.
“Composites also allow a lot of
options for shapes, and give you the
ability to place systems in the structure, such as anten-
nas, as you fabricate it,” said Donny Dorsey, director of
operations for HII’s Gulfport facility. “You can’t do that
with steel or aluminum.”
HII uses the Vacuum Assisted Resin Transfer
Molding process involving carbon fiber fabric, balsa
wood, synthetic foam and a resin system.
“We place layers of carbon fiber cloth over the balsa
core, then seal with a plastic vacuum bag connected to the
resin system. When we evacuate all the air and pull a vacuum on the bag, it draws resin in,” Jenkins said. “When
the material is saturated the resin undergoes a chemical
transformation and cures while inside the vacuum bag.”
If more ballistic protection is needed, Jenkins said
Kevlar fiber or similar material could be incorporated
into the composite for greater protection.
The Gulfport facility has built four ships of the Osprey
class of minehunters for the U.S. Navy as well as composite mast enclosures for the San Antonio class of amphibi-
AUSTAL USA
The Navy’s Joint High Speed Vessels (JHSVs) will feature all-aluminum construc-
tion. Because it is lighter than steel, aluminum structures can be easier to move
and lift during construction. A module for the second JHSV is shown being moved
at Austal USA’s Mobile, Ala., shipyard Oct. 31.
ships were hit by multiple missiles, for example, they
would have been severely damaged regardless of what
they were made of. Detailed investigations into the most
notorious incidents, loss of HMS Sheffield during the
Falklands War in 1982 and the missile strike on USS
Stark in the Middle East in 1987, confirmed that burning of aluminum was not a factor in either case.
“Metals melt, but they do not ‘burn,’ at least in air
at normal atmospheric pressure,” said Rob Moore,
vice president of engineering at Textron Marine &
Land Systems, Slidell, La. “It would be nice if there
were a low-cost, lightweight structural material that
didn’t melt, burn or produce toxic gases when exposed to high temperatures, but such materials only
exist in science fiction. Selection of the most suitable
structural material depends on many factors, and no
one material is going to be the best choice for all
applications. Steel has its place, but so do aluminum,
titanium and composites.
