According to C. Eric Banister's Johnny Cash FAQ: All That's Left to Know About the Man in Black,
"Port of Lonely Hearts" [...] offered an early glimpse at Cash's willingness to experiment with his sound by overdubbing a second vocal line, providing harmony as well as a call-and-response part. “Port of Lonely Hearts,” like several other songs from early sessions, would later be released after Cash had made his move to Columbia.[13]
Cash also recorded a few songs about boats as a means of escape. Initially, in "Port of Lonely Hearts," the narrator is dejectedly waiting for his ship to come in, preferably with a girl on board. He's determined to wait as long as it takes for love to arrive so he can leave the port of lonely hearts with the one he loves.
— John M. Alexander. The Man in Song: A Discographic Biography of Johnny Cash[14]