ARTICLE

July 2004

Navy Gradually Embracing Composite Materials in Ships

by Roxana Tiron

The U.S. Navy gradually plans to incorporate composite materials into the construction of new ships. Although experts agree that composites offer lighter-weight materials that are easier to maintain, the Navy has been wary to pay the higher cost, arguing that traditional materials such as steel can do the job, are less risky and more affordable.

Nevertheless, the Navy claims that its next generation destroyer, the DD(X), will be the service’s first major commitment to composite construction. Northrop Grumman Shipbuilding Systems, the DD(X) prime contractor, is beginning work on a composite deckhouse.

In its selection for the Littoral Combat Ship, the Navy eliminated Raytheon’s design—based on the Norwegian Skjold ship with a composite hull. A senior Navy official told National Defense that the decision does not mean the service is being too “conservative” and walking away from composite ships.

During the selection process, some speculated that a fire, which destroyed the composite Norwegian minesweeper Orkla two years ago, would play a part in the Navy’s consideration.

The official argued that the two selected designs, by the General Dynamics and Lockheed Martin teams, have composite elements.

Composites have gained more clout in the past decade, but they have been used in and on Navy platforms since the 1940’s when the U.S. Navy pioneered the use of fiberglass composites for small boats, said Gene Camponeschi, program manager for composites research at Naval Surface Warfare Center at Carderock, Md. Since then the Navy has used composite materials for the MHC 51 class of mine-hunters and submarine bowdomes.

Secondary applications now being made with composites include rudders, propellers, stairways, handrails, valves and armor.

Among the most complex are the composite mast-enclosures on the San Antonio-class amphibious ship, the LPD 17.

The Navy’s main reasons to use composites on its ships are the reduction in maintenance and weight, said Richard Vogelsong, a scientist at the Office of Naval Research.

Composites generally are made out of two or more different materials combined to form a single structure with an identifiable interface. One of the earliest known composite materials is the adobe brick in which straw—a fibrous material—is mixed with mud or clay—an adhesive with strong compressive strength.

Composite materials are stronger and stiffer than metal, and for the same strength are lighter than steel and aluminum. They also are less susceptible to corrosion.

Ships made of composites are estimated to cost 10 percent to 20 percent more than steel ships, said Jay Foley, vice president of strategic planning for Northrop Grumman’s shipbuilding sector.

“The raw materials are more expensive,” he said. “The training for our construction mechanics is more expensive.” Northrop Grumman has made considerable investments in its Gulfport, Miss., facility to be able to support the composite work and better the manufacturing processes, said Foley during a tour of the facility. The company invested approximately $50 million to modernize the facility for composite work.

Foley said he expected as many as 1,000 people to work at the shipyard in the next two years. “Our challenge is to find, hire and train people,” he added. Northrop Grumman builds ships for both the U.S. Navy and the Coast Guard’s Deepwater program.

The company has found that, even though the Navy has encouraged shipyards to invest in composite manufacturing technology, the sea services have yet to commit long-term funding.

Despite the cost premium, composite ships end up saving money in the long run by cutting down on maintenance and repairs, Foley said. “If I had a pot of money to buy things and another pot to maintain them and I could not mix the money, I would be concerned about the acquisition cost.”

Cultural considerations also come into play. “Intuitively, people who have built ships out of steel or aluminum for decades want to build them out of steel and aluminum. They know how to build them. They know how to price them. They know how to fix them. They know how to attach things to them,” he said.

Composites come with their share of problems. They are flammable, and once aflame they create toxic smoke. These safety-related issues are part of the reason why the Navy has shied away from composites.

“They do not have a lot of familiarity with composites at this point, so it is perceived as higher risk,” said James Sabo, the technical director at the South Carolina Research Authority.

The Navy has researched the risks, said Vogelsong. According to him, ONR has developed certain materials to protect composites from fire, he said.

“Hopefully, we would shut off the source of fire, shut down the fuel, the same way you would do on a regular ship,” said Foley.

One advantage of composites is that they do not transmit the heat from one side of the structure to the other. Foley said risks can be mitigated by the way the ship is built, how the fire system is installed and how well the crew is trained.

Meanwhile, for composites to be more widely accepted, the industry and the Navy still have to improve the process of joining composites with metal structures. They also have to figure out how to inspect and repair those composite structures if necessary.

“The problems tend to arise when you combine manufacturing processes, such as combining metals and composites,” said Vogelsong. “The manufacturing process associated with composites would play a big part in the acceptance of the ship-design community.”

Different shipbuilding processes also are required with composites since they are not purchased, assembled or inspected in the same way that steel is, said Camponeschi.

For example, composite parts are co-infused or bonded rather than welded and ultrasonic inspection versus X-ray inspection techniques are used when composites, he explained.

On the upside, composite materials can make a ship less noisy, less detectable by radar and can help reduce the crew’s workload. For example, the DD(X) will have embedded arrays and no rotating antennas, said Foley. Composites contribute to the overall stealth of the ship, he said.

“You can make the ship stealthy in the original design and keep the ship stealthy, because composite materials do not lose their shape,” Foley explained. Those materials keep their width for over 30 years, which would be the entire lifetime of the ship.

“In a composite structure, you can do the maintenance from the inside ... where it is not raining, or snowing,” Foley asserted. “You get half the size of the crew, because you do not need all the maintenance and [so] you can have much more room inside the ship.”

The use of composites provides more flexibility in the design of a ship, said Barry Heaps, the director of production manufacturing at Gulfport.

“It gives you the ability to increase your parameters, because it is lighter, [and] then you have a menu of selections at your finger tips,” he said. “Do I want to carry more fuel? Do I want to carry more weapon systems?”

Because composites would reduce the topside weight of the ship, some question whether ballast would be necessary to stabilize the ship.

“We do not know, because the design is not mature yet,” said Foley. “Ballast would probably not be required. However, it depends on what systems the customer decides to install in there, what radars, what gun, where the magazine has to be, how much navigation equipment he wants to put up high in the ship.” Should ballast be needed, it can be accommodated in the design, he added.

“By enlarging the size of the fuel tanks and carrying more fuel, by enlarging the size of your weapons magazines, by making the berthing areas more substantive down below in the ship, you would have that wiggle room in the design to make the ship more capable,” Foley said.

Heaps argued that a much lighter ship would allow the Navy to make up the weight with enhancements such as new weapons systems.

“I think that the customer would fill that space up with more stuff that he can put in the ship to offset the requirement for ballast,” said Heaps.

With composite materials, designers have more flexibility, because they can strengthen the ship exactly where needed, said Foley.

Northrop Grumman is working on a series of research and development programs to look at an all-composite high-speed vessel and catamaran.

The company also is trying to convince the Coast Guard to select an all-composite Fast Response Cutter for its Deepwater program. Only ships that are up to 350 feet in length, or smaller, are good candidates for all composite hulls, said Foley. At press time, Northrop was awaiting a Coast Guard decision on the FRC.

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