Loaded with more than 6,000 cargo containers, the ship Ever Living prepared for the final leg of its journey through the newly expanded Panama Canal when things hit a snag: The last of the massive steel lock doors failed to open all the way.

The pilots controlling the ship and the captains of the tugboats tethered to huge vessel opted to continue guiding it through the narrowed passageway, passing nerve-wrackingly close to the side of the locks to avoid running into the stuck door.

“These are things that shouldn’t happen,” tugboat captain Mauricio Perez said. “Sometimes the only thing we can do is pray.”

A little over seven months after authorities launched a much-ballyhooed, $5.25 billion canal expansion to accommodate many of the world’s largest cargo vessels, they have yet to fully work out a significant kink: With little margin for error, ships are still scraping the walls and prematurely wearing out defenses designed to protect both the vessels and the locks themselves.

The Associated Press traveled on a recent voyage by a tugboat guiding the Ever Living through the canal’s Cocoli locks toward the Pacific Ocean. Along the way there were multiple places where the black rubber cushion defenses were visibly worn down, hanging into the water or missing entirely. In one spot a pile of dislodged bumpers sat on the side of the locks, apparently waiting to be hauled away.

Even before the canal opened in late June, tugboat pilots had expressed concern about what they said was insufficient training for maneuvers that are now required — and that are a radical departure from the previous system.

In the old locks, which are still in use, ships get tethered to powerful locomotives on both sides that keep them centered in the canal. In the new locks, that responsibility falls to the tugs, one tied to the bow and another to the stern.

Especially at first, pilots on the bridge of the cargo ships and tug operators would sometimes deliberately nudge up against the barriers as a way to properly align the vessels. That has lessened somewhat, but the battered bumpers are evidence that not all passages are smooth.

“The fears and dangers remain, although the boats are going through,” Perez said. “Throughout the entire maneuver, there are critical moments.”

The Panama Canal Authority attributed the malfunction of the lock door during the AP’s transit to a failure in a water-level sensor caused by vegetation and debris accumulated from neighboring Gatun Lake. It said the problem has been fixed.

According to the authority, between June and January there were only 15 incidents that resulted in damage to locks or ships, or about 2 percent of the 700 total transits through the new waterway. Officials say the first seven months have been a learning process but they are optimistic.

Manuel Benitez, deputy administrator of the canal, said it has been “pretty positive the way our people have been able to navigate that (learning) curve.”

And the incidents reported “have not been of a magnitude that could affect the operation of the locks,” he said. “The ships have not run aground; they continue their routes.”

Still, shipping companies have multimillion-dollar vessels at stake, and any delay due to an accident can cost them money. In perhaps the most serious incident involving the new waterway, a Chinese vessel struck a lock wall a few weeks after the June inauguration, gashing its hull and delaying its itinerary.

The Canal Authority declined to say how much money is being spent on repairing the new bumpers or whether such repairs have been forced ahead of schedule.

Captains who navigate the canal told AP the defenses were anticipated to last at least a couple of years before wearing out. Pilots have argued they should be replaced with a system of floating bumpers like those used in some European locks.

Authorities say they intend to continue to operate with the current system of defenses, though they don’t rule out changes as part of future upgrades.

“Thanks to the expertise of our practices, these incidents are happening less and less,” Benitez said.

Some experts say it’s still early to make a final judgment on the locks’ safety.

“It seems there is a consensus between authorities and captains to pay more attention (to) the issue of the defenses,” said Paul Bingham, vice president of the Boston-based Economic Development Research Group.

“I do not know if it is a design flaw or evidence of how the walls of the locks may need to be better protected,” he said via email. “It is possible that the operations of the tugs in controlling the vessels inside the lock chambers need to be improved as well.”

There have been notable improvements in operations. Average transit times have dropped to 2 ½ to 3 hours, according to the tugboat pilots, compared with 4 hours when the locks first opened. With experience, captains have become more comfortable taking ships straight down the center of the locks, especially when weather conditions are favorable.

But it’s still a delicate operation.

As the 1,098-foot-long Ever Living maneuvered into the 1,400-foot lock chamber, sailors and dock workers tied the ship off right up against the walls to keep it in place while it awaited passage to the next level. The tight space left precious little room for the tugs ahead of and behind the vessel, and tug captains still fear their boats could be crushed against the walls if things get out of control during a squall or high winds.

“They are betting on our professionalism and on improvisation,” Perez said.

Captains also regret that no alignment wall was built at the Pacific entry to the Agua Clara locks, which would help with lining the vessels up and offer protection from strong currents. This is where the Chinese vessel had its accident.

“It is like threading the eye of a needle,” said pilot Alvaro Moreno.