GONZALES — A monumental miscalculation happened somehow in the early morning darkness along the Mississippi River just southeast of Donaldsonville on October 12.

The pilot of the tugboat Kristin Alexis, pushing a large barge up the river, ran the top of a towering crane into the Sunshine Bridge, severely damaging the critical span and disrupting cross river traffic flows for months.

Critical support beams on the metal truss bridge built in the early 1960s were crunched, and commuters and commerce using the bridge daily went from a 10-minute trip to a more than hour-long detour during a shutdown that stretched on for a month-and-a-half.

Beginning Monday, the public will begin to learn what the U.S. Coast Guard and National Transportation Safety Board investigators have been uncovering in the months since the crash.

The agencies are holding a week-long public hearing that is required as part of the formal marine casualty probe opened into the incident. Due the initial estimate of bridge damage — more than $5 million — the Coast Guard must have a formal investigation, which is triggered whenever the damage exceeds $1 million.

The crash involves Marquette Transportation Co., the Paducah, Kentucky-based tug owner, and Cooper Consolidated, a stevedoring company based in the River Parishes that owns the crane barge.

Twenty-four witnesses have been subpoenaed to testify at Lamar-Dixon Expo Center near Gonzales, including the master captain and pilot of the tugboat. 

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Lt. Rachel Ault, spokeswoman for the Coast Guard in New Orleans, said the hearing is a step by the agency, which regulates the nation's maritime industry, before it issues findings and makes recommendations for possible regulatory changes or sanctions against the individuals or companies involved in the incident.

"The Coast Guard is trying to figure what happened and what should come as a result of what happened," Ault said.

The NTSB is focused on the safety implications of the crash and whether broader policy recommendations should be made.

Federal investigators have held information close to the vest so far, and many questions remain about what happened. These include  who was operating the tugboat, what the pilot knew about the height of the bridge and the crane barge, known as the Mr. Erwin and why  the crane was being directed under a side span of the bridge that is 23 to 24 feet lower than the main span.

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The Sunshine Bridge has an arch built into it, so the sides are lower than the center. According to river gauge and other data, the span under which crane was being pushed was about 128 feet above the water at the time of the crash.

The Mr. Erwin is a former coal mining crane used in Columbia that is able to gather 132,280 pounds of material in a scoop. Cooper Consolidated bought the crane in November 2017 and refurbished it, the company says.

The exact height of the crane is unclear, but company officials have said previously the barge's crane arm was down and none of their employees were operating it at the time of the crash.

Marquette and Cooper Consolidated are major players in Louisiana in the nation's inland marine industry. The industry's cargo-moving vessels ply the Mississippi and other major waterways winding through the country's mid-section and coastal waters and deliver an estimated 650 billion tons per year of agricultural, industrial and other bulk freight.  

Marquette, which has 400 Louisiana employees, handles about 15% to 20% of that traffic nationally. Company officials say they do it safely compared with the huge volumes they handle. But the company has had high profile crashes recently in the state.

In May 2018, one of Marquette's 130 tugboats on the Mississippi River system, the M/V Steve Richoux, ran six barges carrying cement into the Mardi Gras World facilities at the public Robin Street Wharf in New Orleans. A Coast Guard investigation remains open but not enough damage occurred to require a formal investigation, Ault said.

In an interview on Friday, Marquette Transportation President Damon Judd apologized for the inconvenience the Sunshine Bridge crash caused to residents who rely on the bridge, calling it a "serious and unfortunate event."

"We take the safety of our operation very seriously," said Judd, who is expected to testify on Saturday.

He declined to get into the details of the crash, citing respect for the investigative process. However, he did say the company has found no evidence that the use of drugs or alcohol, pilot fatigue or mechanical failures in the Kristin Alexis tugboat were a factor in the crash.

He added the company has also found that the incident did not result from a lack of safety policies and procedures at Marquette.

"Things go wrong when you have an incident like this, and our entire safety management system is designed to try to help prevent the risk of human error," Judd said. "But ultimately we rely on licensed mariners and the judgments they make in the wheelhouse of our vessels as they deal with navigating what is a very dynamic system on the inland waterways."

The Marquette crew was moving the crane barge for Cooper Consolidated under what's known as a "fully found charter agreement," where Cooper employees had input into what the tugboat was doing.

"Typically," Judd said, "the way those work, the customer is directing the boat what to do and we, Marquette, as the operator, are responsible for crewing and operating the vessel at that customer's direction."

The first witness up Monday is Desmond Smith, the then-master captain of the tugboat who had overall responsibility.

The pilot, Eugene Picquet III, of Gretna, is set to testify Tuesday. The pilot is basically the second in command whose job includes handling shifts operating the tugboat. 

Judd said Smith and Picquet are no long employed by Marquette. Attempts to reach the men have been unsuccessful.

Follow David J. Mitchell on Twitter, @NewsieDave.