Shouldnt "the ship is not for sale" also work? Ship instead of boat worked on other similar phrases :)
Un bateau n'est pas "a ship", c'est un "boat". "A ship" = "un grand bateau", "un navire" ou "un vaisseau" (le dernier est littéraire).
The reason we are asking is because in other excercises like "je vois un bateau au droite" it was translated as "I see a ship on the right" and the translation with bateau as a boat was marked as wrong!?
Elle semble une bonne question. But even le bateau n'est pas en vente still means "the boat is not for sale".
"On sale", means that there are discount prices. "For sale" means just that it is open to be sold. On black friday, many items are on sale. On any other regular day, items are just for sale.