Well, when I heard Dave van Ronk do "Salty Dog" in 1971 or so at the Main Point in Bryn Mawr (near Philadelphia), he said he had learned the song from Rev. Gary Davis. When he asked Rev. Davis what it meant, the reply was, "Dave, maybe I'll tell you when you're older." By the way, I think van Ronk's version is one of the best.

Aloha,
Mark