Online videos of Branson duck boat tours from recent years show life jackets stowed beneath the roof of the boats, within arm’s reach of an adult. But few if any patrons were wearing them on those trips.

The Coast Guard requires life jackets to be available for each passenger on a boat, including duck boats, but allows the crew to decide when to instruct passengers to put them on.

Jim Pattison Jr., the president of Ripley Entertainment, which acquired the Ride the Ducks attraction in Branson last year, said the boats were always stocked with life jackets, but that people were not required to wear them. The weather was calm when the boat left the dock on Thursday. Mr. Pattison said this was the first such accident at Ride the Ducks, which was started more than 40 years ago.

In an interview, Mr. Pattison said the company had policies in place to keep boats off the water during dangerous weather, but he was unsure of the exact threshold for aborting a tour. “I was told that it was calm” when the boat went out on the water, Mr. Pattison said. He said the boats typically spend 15 to 20 minutes in the water on a circular route through Table Rock Lake.

“This is a real tragedy, and we can’t say enough about how devastated we are,” Mr. Pattison said. “It’s hard to think about.”

Duck boats are modeled after DUKWs, which brought materials ashore during the invasion of Normandy and hauled howitzers during the landings in Iwo Jima. In the decades since, duck vehicles have been used to transport tourists in places like Philadelphia, the Wisconsin Dells and Branson.

Such boats have had mixed safety records over the years, both on water and land. In Philadelphia in 2010, a duck boat that stalled in the Delaware River was struck by a barge being towed by a tugboat, killing two people. On land, pedestrians and a motorist were killed in recent years in accidents involving the vehicles in Philadelphia and Boston. In 2015, a duck boat collided with a bus in Seattle, killing five people.