When the 78-foot wooden ketch Notre Dame des Flots sails into New York harbor in August, people will rejoice. For packed into the hold will be many barrels of Muscadet-Sur-Lie, a “bright and crisp” white wine from Nantes, France. A music and dance festival, sponsored by a French (who else?) wine bureau and called Muscadet, The Impressionist Moments, will take place on Aug. 12 at South Street Seaport’s Piers 16 and 17, featuring barrel rollers, live dancers, musicians, freshly prepared seafood dishes, and, of course, the wine itself. The wine will be available for sale; the performances are free. “This is a celebration of the tradition, during the Impressionist period, of bringing wine by boat to Paris for the waterside cafés, which were called guingettes,” said Tanja Yokum, a spokesman for the Conseil Interprofessionnel des Vins de Nantes. The vessel will continue to Montreal for a festival on Aug. 17. Another vessel, Cardinal, will load wine and head for New Orleans for a similar guinguette celebration on July 30.