SAN FRANCISCO -- Something didn't seem right to ship pilot John Cota when he inspected the bridge of the freighter Cosco Busan at dawn.

The ship gleamed with state-of-the-art electronic charting equipment and two radar displays that penetrated fog and darkness, but these vital instruments seemed out of whack, he told investigators.

According to Cota, he grumbled to the ship's captain, but the captain's replies reassured him enough that Cota guided the vessel out of its berth at the port of Oakland.

But as the 901-foot ship slipped into a bank of fog, the radar conked out, and the confusion over the electronic charts resurfaced at a critical moment, according to Cota's account. Catastrophe struck moments later.

The instruments are emerging as focal points as the National Transportation Safety Board examines what caused the ship to sideswipe the San Francisco-Oakland Bay Bridge last week, opening a gouge in its hull and dumping 58,000 gallons of sludge-like bunker fuel into San Francisco Bay.

Earlier this week, the Coast Guard ruled out mechanical failure, pointing strongly to human error, including communication problems and "bridge-management issues" among a crew that was new to the ship.

But the NTSB, which took over the safety aspect of the accident, re-interviewed witnesses and participants under oath, and is studying the possibility of equipment problems, board member Debbie Hersman said.

One of the board's first tasks was to re-interview Cota, among the most experienced of the seamen who guide ships through the bay. After lengthy sessions with Coast Guard investigators, he was questioned again for about three hours this week by the NTSB.

Cota has not spoken publicly since the accident -- the bay's worst oil spill in nearly two decades -- killed hundreds of birds and forced the closing of beaches throughout the area. But in news briefings and in interviews with The Associated Press, the NTSB provided many details of the pilot's account.

The NTSB emphasized that Cota's account represents just one side of the story, and it is trying to verify his version of events with other witnesses, records and other evidence.

For instance, the NTSB brought in a private expert to analyze the radar and electronic charting devices, Hersman said. That analysis found no problems with the instruments, she said Wednesday.

"The radar technician looked at the electric chart display as well as the radars -- there are two radars," Hersman said. "He responded that they were performing as expected…We want to corroborate this information with the VDR (the Voyage Data Recorder) that takes samples of the radar every 15 seconds."

NTSB experts are also analyzing the ship's voyage data recorder, which captured radio transmissions and radar images that could validate Cota's account.

In other developments:

-- The Coast Guard has replaced the officer overseeing the response to the spill, Capt. William Uberti. The agency has been criticized for allowing a lapse of several hours between when officials knew the spill was 58,000 gallons -- not 140 gallons as initially reported -- and when that information was made public.

-- Members of the Chinese crew have hired lawyers and are refusing to speak with investigators.

Cota boarded the Cosco Busan -- a relatively new ship, built just six years ago -- at 6:20 a.m. last Wednesday. The container ship, owned by a Hong Kong company, was bound for South Korea.

Fog blanketed the port, so the ship's departure was delayed for about 90 minutes. While he inspected the equipment and spoke with the crew, he told the NTSB, he grew concerned about two automatic radar plotting aids.

The collision-avoidance devices find, or "acquire," physical objects, known as "targets," and track them by placing a digital ring around them on a monitor, said Tom Roth-Roffy, the NTSB's chief investigator on the case.

While waiting to depart, Cota told investigators, he saw "clutter" on the radar, according to Roth-Roffy.

Cota told investigators "some of the targets were not being automatically acquired," Hersman said. But after making some "routine operator adjustments, he became satisfied with the equipment," she said.

Also while waiting to depart, Cota expressed concerns to the captain about a second piece of equipment known as ECDIS, or electronic charting and display information system, he told investigators. The system uses symbols to mark lighthouses, buoys and such objects as bridge footings.

There were discrepancies between the symbols Cota was seeing on the electronic chart's screen, and those on the ship's set of paper charts, according to Cota.

Again, Cota said, he pressed the ship's captain. And again he accepted an assurance from the captain, Cota told investigators.

The fog began to lift, and Cota and the captain agreed they could set out. They pulled away at 7:48 a.m. Visibility was between a quarter-mile and a half-mile, Cota told investigators, and a tugboat pulled the mammoth cargo ship out of its berth.

But before the vessel had even made it out of the channel leading from the port, the fog closed in again, and Cota switched to radar as his primary means of navigation, he told the NTSB.

He aimed the ship for the biggest opening between the towers that support the Bay Bridge, a gap of more than 2,200 feet.

Coast Guard Commandant Adm. Thad Allen said the Cosco Busan was traveling "pretty fast" for the conditions. But the tug captain, whose vessel was now trailing the freighter, told the NTSB the Cosco Busan was moving at about 10 or 11 knots -- "a manageable speed, but you really had to be on top of your game," Hersman said.

As he was turning the ship, the radar again "distorted" and "unreliable," Cota told investigators.

He switched to the electronic charting system, and renewed his discussion with the captain about what certain symbols meant, he told investigators. The captain told the pilot what he believed they represented.

It was about this time that the Coast Guard's Vessel Traffic Service -- the equivalent of air-traffic control for bay shipping -- radioed the Cosco Busan to ask about Cota's intentions.

Cota told them his plan and steamed ahead, though it is not clear he knew where he was going.

Moments later, the bow lookout radioed the bridge an urgent warning: The Cosco Busan was about to strike the bridge. Cota realized it at about the same time and ordered the helmsman to turn the ship hard, he told investigators.

That appears to have averted a head-on crash into the tower, one that could have crippled the bridge and possibly caused more destruction to the ship.

As it was, three tanks were damaged, allowing the bunker fuel -- which environmentalists call "the dirtiest fuel on the planet" -- to escape into the bay.