New US Navy destroyer’s seaworthiness, stability questioned

FILE - In this Oct. 31, 2013 file photo the Navy's stealthy Zumwalt destroyer is built at Bath Iron Works, in Bath, Maine. The Navy's largest destroyer cuts an imposing figure: massive in size, with an angular shape, hidden weapons, and an unusual hull that fell out of favor a century ago in part because it can be unstable. How this unusual hull shape works in rough seas will be answered when the ship heads to sea in December. (AP Photo/Robert F. Bukaty, file)

BATH, Maine (AP) — The largest destroyer built for the U.S. Navy cuts an imposing figure: massive, with an angular shape, hidden weapons and antennas, and electric-drive propulsion. But underneath the stealthy exterior resides a style of hull that fell out of favor a century ago in part because it can be unstable.

The Navy will soon learn how this modern take on the “tumblehome” hull holds up when the first-in-class Zumwalt heads out to sea in December for builder trials in the rough-and-tumble North Atlantic.

Amy Lent, of the Maine Maritime Museum, which works closely with the shipyard, said taxpayers needn’t worry because the Navy and shipbuilder Bath Iron Works have “tested the hell out of it.”

“This is an enormous investment. There’s so much at stake. They’re not slapping something together and sending it out to sea,” she said. “I think they’re pretty confident. They know what they’re doing.”

Designers chose the hull style associated with pre-dreadnought battleships, but this warship looks nothing like one from President Theodore Roosevelt’s “Great White Fleet.”

The inverse bow juts forward to slice through the waves. A composite deckhouse hides radar and antennas, giving it a clean look. Sharp angles deflect radar signals.

Typical of tumblehomes, though, the hull slopes inward above the waterline, giving the Zumwalt something of a pyramid shape. The shape can cause problems in certain conditions, critics say.

Concerns have been voiced in the ship-design and shipbuilding communities about the warship’s overall stability — and any instability could be exacerbated if there’s battle damage, said Matthew Werner, dean at the Webb Institute, which teaches naval architecture and marine engineering in Glen Cove, New York.

But the hull’s sloping sides contribute to the Navy’s goal of stealth. The Navy contends the 600-foot-long, 15,000-ton behemoth will look like a small fishing boat on enemy radar.

“It’s a true engineering challenge. They’re trying to make a ship with stealth characteristics that requires certain shapes. To do that they have to compromise,” Werner said.

Norman Polmar, a naval historian, analyst and author who is sometimes critical of the Navy’s decisions, said he has no qualms about the Zumwalt’s seaworthiness after a large-scale model was built to prove the concept.

The Navy has built a modern version of the tumblehome that utilizes computers to aid in stability, much like the Air Force used computers to transform a flying wing — the B-2 bomber — into a stable aircraft. “The technology today makes that concept doable and much more efficient,” Polmar said.

The ship is 50 percent bigger than the current generation of destroyers but has advanced automation to reduce the crew size. It’ll use turbines similar to those used in a Boeing 777 to create electricity to drive the ship. It’ll have new radar and sonar, and powerful guns with rocket-propelled projectiles.

The Navy, which views the ship as an important part of the Obama administration’s Asia-Pacific strategy, can’t afford a flop after the cost of the first ship ballooned to at least $4.4 billion and construction fell behind schedule.

“The Navy has validated the ship’s design through extensive computer modeling and simulation, as well as scale model testing in various sea states, speeds and weather conditions. We are confident the design is safe, that the ship is seaworthy, and its operating parameters are known and understood,” said Capt. Thurraya Kent, a spokeswoman.

Bath Iron Works will be testing the ship’s performance and making tweaks this winter. The goal is to deliver it to the Navy sometime next year.

By David Sharp, The Associated Press

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