FOURAS, France — With Champagne, fireworks and a presidential blessing, a painstakingly built replica of the frigate once used to bring French troops and funds to American revolutionaries is setting sail for Boston. Lafayette set sail on March 21, 1780, arrived 38 days later in Boston, and played an important role in the revolutionaries’ ultimate defeat of Britain. Using captains’ logs and manuscripts from the era, maritime experts and historians ensured that workers used the same construction materials and methods as those used to build the original. Volunteer crew members will sail the frigate, with “Hermione” carved across its stern, across the Atlantic. Firing its cannons, the ship left the La Rochelle port earlier this week for a test run, escorted by sailboats and watched by thousands of cheering supporters on shore, some waving American flags. “I wanted to push this experiment to its logical extreme, so I prepared a full 18th century wardrobe based on after-death inventories I found in the Paris archives and artwork from the period,” he said.