Once one puts narrative in a song, it gives it some stability and discourages any improvisation aside from superficial variations... unless there is co-exists the memory of the genre as one meant for improv.

The following specimen uses the Solomon Grundy ~narrative again (seen above in L.A. Smith).

I know nothing of the author. It's a pseudonym, and the book is fiction. It's set first in the 17th century and then jumps to the 19th; Fitzerse is a time-traveller. "Ranzo" is first included in the 17th century part, and then comes back. The words, while typical enough, don't obviously match any prior publication that I know of. The author might just as well have cribbed them from a piece of writing as heard them sung by sailors directly.

Fitzerse, Alfred [pseudonym]. The Trance of Fitzerse: A Tale of Two Centuries. London: The London Literary Society, 1888.

pp 37-38
//
        The incidents of the voyage, with very few exceptions, were such as have often been related of others. The utmost order prevailed. The weather was favourable, though at times the wind was high and the sea rough. Alfred Fitzerse was not long in making friends with all on board, and growing accustomed to this new life. He was greatly interested in the manners and customs of the sailors, whom he found, in general, to be good-natured men, though somewhat rough and overbearing towards each other. What struck him most was their cheerfulness, by which he thought they had fairly earned their common title of jolly tars. Whenever they were called upon to act in concert, they always supported each other by singing some song, the refrain of which was the signal for a united effort. One such song in particular impressed itself upon his memory, and it may be interesting to some who read these lines:

“Ranzo was born on a Sunday,
   Ranzo, Boys, Ranzo !
He went to school on a Monday,
   Ranzo, Boys, Ranzo !
He ran away on a Tuesday,
   Ranzo, Boys, Ranzo !
He went to sea on a Wednesday,
   Ranzo, Boys, Ranzo !
He was rated mate on a Thursday,
Ranzo, Boys, Ranzo !
   He was cast away on a Friday,
Ranzo, Boys, Ranzo !
   He skipped the deck on a Saturday,
Ranzo, Boys, Ranzo!”

   The sailors could not give any coherent account of the origin of this song. They said they had picked it up from one another, and that they supposed Ranzo, if such an individual had ever existed, was some Portuguese sailor of whom his shipmates had made a kind of hero.
//


Pp287-8
//
While we were still engaged in conversing upon indifferent matters, my ear caught the strain of another song the sailors had started on deck and I thought I would go and listen to it. On reaching the place I was nearly thrown off my balance by what I heard, acting as it did in the way I have found any sudden reminiscence of my former state to do upon my mind. Could I believe my senses? There was the whole history of Ranzo, the mythical Portuguese, from his cradle to his watery grave, recited in the same sing song strain which I had often heard on board the “Trustwell.” The same emphatic chorus, too, confirmed it, as the singers hauled together with a will:

Ranzo, boys! Ranzo!

   “That's an old song,” I remarked to the third officer who was standing by. “Do you know where the sailors picked it up?"
   "Hard to tell that,” said he. “Old Blowhard there would say, if you asked him, that Shem, Ham and Japhet had sung it in the Ark when Adam was an oakum boy in Chatham Dockyard."
//

The text also quotes "Haul the Bowline" in the 19th century episodes.