"I remember hearing it sung at the Bay of Islands (N.Z.), about 1877, when there were quite a dozen Yankee whalers at anchor refitting. Ranzo was a gay dog who made love to the skipper's daughter, and finally marrying her, got the berth of chief mate aboard her father's vessel."
And here's a nice vignette. A lade named Alice Hope Watkins recalled a childhood voyage on the clipper "Royal Dabe" in the early 1870s (Brisbane "Courier-Mail," Jan. 1, 1921):
"To wake in the night, hear the thud of hurrying feet, shouting voices overhead, as to know blank terror, till the comforting roar of 'Ranzo, Boys, Ranzo!' brought a sense of security, despite creaking cordage, and the buffets of wind and water. Never were there happier children!"