This comes as investigators focus on why the Seastreak ferry's engines may have failed in Wednesday's accident.
About 70 people were injured when the ferry crashed into a pier.
Its engines have a data recording feature that investigators will try to access.
Investigators interviewed the ferry's captain, Jason Reimer, for nearly three hours on Thursday, and he told them there was a mechanical failure onboard, he was unable to put the ferry in reverse when he tried to dock and the engines later died.
Sumwalt said the ferry captain told investigators that as the vessel approached the dock, he moved from a central console to one on the starboard, or right, side of the vessel, as was customary. When he tried to put the ferry in reverse, it didn't work, Sumwalt said. He quickly switched back to the center, but reverse didn't work there either, he reported.
At the time the ferry smashed into the dock, it was going about 13 mph, which is fast for the usual crawl into the slip but not necessarily for turning into the area, experts said. After the impact, the boat was able to dock normally.
The ferry had recently undergone a major overhaul that gave it new engines and a new propulsion system, and officials are looking into whether they played a role.
The ferry's engines were made by a company in Michigan, and representatives are going to the scene to help extract any data from them. There also were video cameras on board, and investigators are trying to determine whether the footage will help them determine what caused the crash.
Sumwalt said investigators also have interviewed the crew and first responders and will be on scene for about five more days.
"There's still a lot of work that needs to be done," he said.
Investigators have called for any amateur footage of the crash, because data have been scarce. They set up an email address, witness(at)ntsb.gov, for people to send images. They already have received some footage from a first responder and a passenger.
Even under normal conditions, safely landing such a large vessel is a sensitive endeavor that requires deep skill.
In 2003, 11 people were killed when a Staten Island Ferry crashed into a pier after its pilot passed out at the wheel. In 2010, three people were badly hurt and about 40 were injured when the same ferry hit the same pier because of a mechanical problem.
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