Tuesday, December 1, 2015

WORLD New U.S. Navy Destroyer’s seaworthiness, stability questioned

 

 

The largest destroyer ever built for the U.S. Navy cuts an imposing figure. But underneath its exterior is 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 trials in the rough-and-tumble North Atlantic.

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

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

The ship’s inverse bow juts forward to slice through waves. A composite deckhouse hides radar and antennas, lending a clean look, and its sharp angles deflect radar signals.

As is typical of tumblehomes, the hull slopes inward above the waterline, giving the Zumwalt something of a pyramid shape, which 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 — especially since any instability could be exacerbated if damage is sustained during battle, said Matthew Werner, dean at the Webb Institute, which teaches naval architecture and marine engineering.

But the hull’s sloping sides contribute to the Navy’s goal of stealth. The Navy contends the 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 concerns about the Zumwalt’s seaworthiness after a large-scale model was built to prove the concept.

“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 will use turbines similar to those on a Boeing 777 to create electricity to drive the ship. It will also have new radar and sonar, and powerful guns with rocket-propelled projectiles.

“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.

The goal is to deliver the ship to the Navy sometime next year.

 

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