A Navy ship had "negative results" searching for a "pinger" that would signal wreckage of the sunken cargo ship El Faro, the National Transportation Safety Board said Tuesday evening.
The USNS Apache is still searching, but switched Tuesday to using side-scan sonar towed behind the search ship.
The Apache's crew began searching Friday using a "pinger locator" that's also towed and is designed to home in on sounds from a beacon-like device planted on El Faro's voyage data recorder, the ship equivalent of an airplane's "black box."
The crew stopped trying to locate the pinger Monday, said an update emailed by Peter Knudson, an NTSB spokesman, but it's not clear why no signal had been found. The Apache has been searching a 10-by-15 nautical mile area near the Bahamas where the ocean is about 15,000 feet deep.
The lack of a signal "may be affected by the orientation of the vessel as it lies on the sea floor or the current condition and functionality of the El Faro's pinger," the statement said.
Time was running short, anyway. The pinger was powered by a battery meant to operate for 30 days after El Faro sank Oct. 1 near the eye of Hurricane Joaquin, meaning it wouldn't have been expected to transmit past this week.
The sonar search is expected to continue for about two weeks.
NTSB scheduled another update on the search for late morning or early afternoon Wednesday.