Here is another 18th century image of a boat with a lug sail.  This is, I think, by the brothers Ozanne, and is of a boat in Cherbourg.  I have been looking through La France Maritime au Temps de Louis XV et Louis XVI: Gravures et dessins des frères Ozanne.  Peintures de Joseph Vernet by Alain Boulaire (ISBN 2-911468-75-9).  I haven’t made an effort to read the French text, yet.