 Originally named "Mark Twain" Steamboat when the park opened in 1955, the stately, 5/8-scale stern-wheeler was the first functional riverboat to be built in the United States for fifty years.Other Disney riverboat attractions now appear at Walt Disney World, Tokyo Disneyland and Disneyland Paris.Passengers wait for the 150-ton, , riverboat, which departs every 25 minutes, inside a sheltered area in the Frontierland section of the park.