Where does the phrase steady as she goes come from?

This is, originally, a maritime reference. Ships were given maiden names because of the life-and-death relationship between sailors and their ships. It may seen archaic to some today, but, the idea is that "you take care of her and she'll keep you alive". So, that is the "she" part, the ship. "She" is going through the difficult waters, (synonymous with a difficult situation), you, (synonymous with the sailor), are to keep things "steady" as "she goes" through them. {Reference British Naval History, United States Naval History, Dutch Naval History}