prone aluminum plates Yards replacing corrosion

prone aluminum plates Yards replacing corrosion

The crack in the hull of an aluminum high-speed catamaran last December in Hawaii triggered an investigation by the vessel's builder, its owner and the U.S. Coast Guard to determine the cause. Similar problems soon became apparent in other vessels recently built on the U.S. West Coast. The unexpected consensus: Some aluminum plates made of 5083-H321 composition used for recent vessel construction were found not to be resistant to corrosion in a saltwater environment.

In the past, builders of aluminum vessels had successfully used both 5083-H321 and 5083-H116. Although the two grades of aluminum differ somewhat in their physical characteristics, both have been generally referred to as marine grade and used in saltwater environments.

After December's discovery, the shipyards moved quickly to fix all damage, including replacement of undamaged but nevertheless noncorrosion-resistant aluminum as determined by testing.

Nichols Bros. Boat Builders' initial response was typical. A boat it had built for service in Southern California was found to have cracks in the middle of 3/16-inch-thick aluminum plates mainly in the engine room and water jet pump room.

"We brought the boat back into our yard and ran a double shift," said Matt Nichols, president of Nichols Bros. "We had to lift the deckhouse off, and replaced with all new material some longitudinal stringers, plates and anything attached." The work, he said was "taken care of by us at great expense, but the customer is extremely pleased."

At Kvichak Marine Industries, the response was equally fast to resolve the problems when the first reports came of defoliation and cracking of the aluminum hull on the Hawaii catamaran.

The Coast Guard's Puget Sound Marine Safety Office identified Nichols Bros., Kvichak Marine and Norsco Marine as the shipyards affected, and Reynolds Metals Company, Alcan Aluminum Corp. and Integris Metals as suppliers of the material.

The extent of the problem is still unknown. In a lawsuit, Nichols Bros. contended "the problem could affect at least 25 vessels built by several shipyards and their total value could exceed $50 million."