ous transport dock ships. The mast structure’s composite
core is made of frequency-selective foam that allows energy of specific frequencies to pass in and out of the mast.
The enclosure protects the radars and equipment inside
from the elements, so they need less maintenance, too.
According to Sten Vallbo, a senior sales executive at
Kockums AB, Karlskrona, Sweden, a unit of Germany’s
ThyssenKrupp Marine Systems, which built the Visby-class all-composite corvettes for the Swedish Navy,
both the Swedish and the Danish navies are operating
steel ships and composite ships so they have actually
been able to compare the maintenance costs.
“They both came to the same conclusion,” he said.
“The hull maintenance cost is 80 percent lower for a composite ship compared to a steel ship in the same size. The
reason is, of course, that they do not have any corrosion
in their composite hulls. The reduced need for maintenance is a contributing factor to reduce the life-cycle cost.
“However, the biggest contribution to reduce life-cycle cost in the case of composite ships is the low fuel
consumption as a result from the low structural
weight. The structural weight for a composite hull is
typically 30 to 50 percent lower than for a steel hull.”
Titanium
The Soviets designed and built entire classes of titanium
submarines. As a structural material, titanium has
increased stiffness and strength when compared with aluminum, and lighter weight and equal or better strength
when compared with steel. Therefore, the areas of ship
design with the highest payoff for the use of titanium are
areas where high stiffness and strength to structural
weight are required, according to Gene Mitchell, the technical warrant holder for welding and fabrication processes with Naval Sea Systems Command (NAVSEA).
It’s very difficult to make the case for the construction of an entire ship from titanium because of the high
up-front costs. But Mitchell said there is a compelling
argument for investing in further research on titanium
for ship structures.
“A number of years ago, NAVSEA developed a notional
surface ship design to determine the significant structural
attributes of a titanium ship for material comparison
studies, so titanium ships are certainly far more than just
‘possible,’” he said. “Typically, in ship design, these attributes are required for the superstructure or deckhouse of
surface ships or for deep submergence vessels.
HUNTINGTON INGALLS INDUSTRIES
The deckhouse of the Zumwalt-class DDG 1000 destroyer is the largest all-composite structure ever fabricated. With
composite structures, less topside weight improves stability and has speed and fuel efficiency benefits.
