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The Honolulu Advertiser

By William Cole

Posted on: Sunday, July 12, 2009

Navy ship grounding detailed

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Here are a few more details of the Feb. 5 grounding of the guided missile cruiser Port Royal in 14 to 22 feet of water off Honolulu International Airport's reef runway.

The Advertiser ran a story Tuesday about the grounding circumstances based on the Navy's Safety Investigation Board findings on the accident.

The 567-foot ship was under way at 8:45 a.m. on its first day of sea trials after $18 million in repairs in the shipyard. The fathometer, for determining water depth, was broken, according to the safety board.

At 12:01 p.m., the Voyage Management System's primary input at the chart table was shifted from a forward Global Positioning System to forward Ring Laser Gyro Navigation.

The Voyage Management System, a digital navigation system that does away with paper charts, dead-reckoned the ship three times and replotted the Port Royal 1.5 miles from its previous position. Ring Laser Gyro is an inertial navigator.

Ship logs indicate a position error between GPS and the Ring Laser Gyro for the duration of the ship's time at sea. The Voyage Management System plotting was based on the inertial navigation and not the required GPS, and the error was not noted by any watchstanders, the report states.

"The quartermaster of the watch continued to plot fixes as satellite fixes when (Voyage Management System) was aligned to receive (Ring Laser Gyro) input," the safety board said. "The bridge team did not recognize the input difference on the (Voyage Management System) display, and relied on VMS without question."

The report said that when the input was switched, the Voyage Management System "indicated numerous positional difference alarms that were not addressed."

Why or how the navigation system was changed is not addressed in the report, which notes a 3,600- to 3,700-yard ship position shift to the east.

That evening, small boats were operated to return aviation assessors to shore.

At about 8:03 p.m., the Port Royal was soft aground, with its bow's underwater sonar dome on the reef, the report said.

The safety board report said there were several factors that led to a Ring Laser Gyro position error, including no evidence of a 72-hour calibration, and the fact that the last reset was four days earlier, meaning the system was not getting new GPS data. There was a "large position error" with the GPS interface not enabled, the report said.

The board, however, rejected navigation equipment error as the cause of the mishap.

"Other means were available to assess the ship's position," the report said. Those included "distinct visual aids" such as the airport control tower. Or, as one commentator on the earlier Advertiser story put it: "There is no substitute for the Mark One Eyeball."