Cardboard boat enthusiasts descend on Salem Maritime National Historic Historic Park in Salem, Massachusetts for The Great Salem Maritime Cardboard Boat Regatta. The regatta is one of several events held during the annual Salem Maritime Festival, celebrating the city’s rich maritime history. A cardboard boat shaped like a rubber duck.The boats in the competition may only be made with corrugated cardboard that is not treated with any sealants. CREDIT: National Park Service. CREDIT: National Park Service.