Investigators who found the sunken freighter El Faro's "black box" will not be able to retrieve the recorder on the current trip.

The National Transportation Safety Board on Wednesday said there are a number of obstructions that will require specialized deep-water salvage recovery equipment to free the ship's voyage data recorder.

The 790-foot freighter sank last October after losing propulsion while traveling between Jacksonville and Puerto Rico. The ship got caught in Hurricane Joaquin, and sank in 15,000 feet of water near the Bahamas. All 33 crew died.

The NTSB did not say when it would return to get the recorder, but hopes it will be done within the "next several months."

The recorder may hold audio from the ship's bridge that can shed light on its final moments.