PORTLAND – The Navy’s mainstay Arleigh Burke destroyers are subject to structural damage under higher-than-anticipated loads in rough seas, necessitating nearly $60 million in upgrades for the entire class of ships.

Nine of the DDG-51 ships have suffered internal structural damage to their bows, which rise and fall, slamming into the water during stormy weather.

A Navy spokesman, who put the total repair cost at $58.9 million, suggested defense industry reports of “serious structural defects” were overblown.

“All DDG 51-class ships retain their full operational capabilities and can perform all operational commitments,” Lt. Cmdr. John Schofield said Wednesday from the Pentagon.

Repairs will ensure that the ships fulfill their projected 35-year service life.

There will be 52 of the $1 billion guided-missile destroyers in service once the USS Sampson is commissioned on Nov. 3, and another 10 are being built at General Dynamics’ Bath Iron Works shipyard in Maine and Northrop Grumman’s Ingalls shipyard in Mississippi.

The shipbuilders are strengthening the bow structure on ships that are under construction, and recently delivered ships are getting repaired after post-shakedown cruises. The remainder of the ships in the fleet will be repaired during future docking opportunities.

Bath Iron Works, which built the first Arleigh Burke destroyer, was not aware of the problems until 2003, more than a decade after the first ship went into service, Jim DeMartini, a shipyard spokesman, said from Bath.

The ships were built to the Navy’s specified standard, but it turns out that real-world sea conditions exceeded the standard, he said.

“What you’ve got here is a situation in my opinion with Mother Nature’s ability to create conditions in the real world that go beyond our ability through scientific or engineering methods to predict,” DeMartini said.

The damage, discovered between 1993 and 2003, includes dents of shell and deck structures of the bow “and was only discovered under close inspection,” Schofield said.

The problems were first reported by Jane’s Defence Weekly. Repairs will consist of reinforcing bulkheads and other structural components, officials said.