HYANNIS — Two experienced operators were in charge of the Cape Cod ferry that slammed into a jetty Friday night in rough seas and injured 15 people, officials said Saturday.

The cause of the accident, which occurred around 9:30 p.m. near the end of a Nantucket-to-Hyannis trip, is under investigation by the Coast Guard. The ferry’s operator, the Steamship Authority, said Friday night’s high winds and choppy seas may have played a role in the crash, though other vessels operated without problems.

Steamship Authority General Manager Wayne Lamson estimated the ferry was traveling at 32 knots, or about 38 miles per hour, when it hit the jetty.

He said that is the maximum speed for that part of the harbor, but it’s “not unusual” for boats to travel that fast in the area.

“You would have thought there would have been more damage than that, given the speed,” Lamson said in a telephone interview.

Maritime maps show that the ferry, called the Iyanough, typically curls northeast on its way to the harbor and steers clear of the long jetty that juts into Hyannis Harbor.

Lamson said the ferry was not necessarily taken off course. Ferry operators, he said, have “some discretion” to chart a course. “But it was definitely in the wrong place” by the time it hit the jetty, he said.

Public safety and Steamship Authority officials said they would not comment on the cause of the accident until the investigation was over.

“Coast Guard investigators were on board the vessel early this morning. They interviewed the crew. They’re photographing the condition of the vessel, interviewing passengers if necessary,” Lieutenant Matt Baker said during a Saturday afternoon news conference at the ferry terminal. “So it’s a thorough investigation, the goal of which is to learn anything we can, make sure future incidents are avoided.”

Baker had no estimate for how long the investigation might take.

The National Transportation Safety Board, which investigates transportation accidents, said it was aware of the accident and working with the Coast Guard.

Ferry passenger Sarah Villafranco, an emergency room doctor who lives in Carbondale, Colo., was sleeping when the impact of the crash woke her.

It was a “very, very sudden, very severe stop,” she said, and the ferry broke out in “a little bit of just low-level pandemonium.”

When a crew member started calling for a doctor, Villafranco rushed to help a man who had fallen from the upper deck and was unconscious.

All around her, she said, passengers had scrapes and other minor injuries.

“Anyone who had been in any sort of standing position was thrown to the ground by the impact,” she said. “A couple of goose eggs on people’s heads, and a lot of us had whiplash-type soreness in our necks.”

Later that evening, when Villafranco…