The captain of the doomed El Faro asked his bosses if he could change his route the day before the US cargo ship sank near the Bahamas, it has emerged.

The ship's owners TOTE Maritime shed responsibility, telling US Coast Guard investigators Tuesday that Michael Davidson did not need to ask permission before taking a slower route.

El Faro sank when it was caught by Hurricane Joaquin on October 1, killing its entire crew of 33 people, mostly Americans and five Poles.

The ship, in operation for four decades and measuring 790 feet (240 meters) long, was transporting several hundred shipping containers and automobiles from Jacksonville, Florida to San Juan, Puerto Rico.

The families of 10 sailors who died in the tragedy accepted a settlement of $500,000 each, while families of the remaining victims have filed complaints with TOTE Maritime.

But the captain's message to change route was no more than a courtesy, as management does not make such decisions, TOTE vice president of marine operations Phil Morrell told the coast guard investigators.

"He does not need permission to ask, he only has to advise us if he's making a change of course. It's more or less a one-way conversation," Morrell said.

Morrell insisted the ship's route was the captain's "total responsibility," adding that such changes in trajectory, which cause a delay in deliveries, were common for cargo ships.

Investigators with the National Transportation Safety Board found the ship's wreckage some 15,000 feet (4,500 meters) below the ocean surface, but it was missing the black box that could have provided more information about the accident.