La fille à l'envers (1974)

As a young girl living in an institution for girls where the nights are restless, Iphis decides to accompany her godfather who is going on a cruise on a yacht. To avoid the problems that would be caused by the presence of a young woman on board, Iphis, dressed as a boy, pretends to be the nephew of the man who is actually her godfather. Seeing her advances rejected by her uncle, Iphis, thanks to her disguise, seduces in turn the sailor, the son of a friend, a pretty girl hired as second mate and the real sailor. This removes all scruples from the uncle for the rest of the voyage.