Thing is, if the camboose can come ashore and get mounted on a flatcar, then it's not too far a stretch for the seagoing cook shack to have been called a shanty. The cook would then become a shantyman, singer or not:

“The enjoyments of the voyage – these I will describe, as they show something of a whaler's life – in no slight degree depend on the crews having some one skilled in the violin to stir the dance on calm evenings. Generally the accomplishment is considered necessary in the “doctor” (i.e., cook) of the ship; and if the cook is black, the chances are that a fiddle is stowed in his sea chest. We had a beau ideal “doctor” and fiddler, and his enlivening medicine went far to banish scurvy from the ship. The second importance is the “minstrel boy.” He must have considerable range of expression, that he may sing of love, war, and the storm; to soothe us with the sentimental and cheer us with the comic. He must sing with Castillego:

“How could we love, if woman were not:
Love, the brightest part of our lot;
Love the only chance of living;
Love, the only gift worth giving.”

Or, with Dibdin:

“Yet, come but Love on board,
Our hearts with pleasure stored,
No storms can overwhelm;
Still blows in vain,
The hurricane
While Love is at the helm.”

Touching on the known constancy of Jack, and the temptations of this wicked world:

“Some faces are like charcoal, and others like chalk-
All are ready one's heart to o'erhaul;
'Don't go for love me.' ' Good girl,' said I, 'walk;
For I've sworn to be constant to Poll.'”

He will shock our native modesty by singing of the sights prepared in the ballet:

“And she hopped, and she sprawled, and she spun round so queer-
“twas, you see, rather oddish for me;
And so I sung out, 'Pray be decent, my dear;
Consider I'm just come from the sea.'”

He sings the joys of virtuous love thus:

        “No gallant captain of the British fleet,
        But envies William's lips those kisses sweet.”

And of the sterner duties of our hardy profession:

        “Cease, rude Boreas, blustering railer!
         List ye landsmen unto me,
        Listen to a brother-sailor
         Sing the dangers of the sea.”

If need be, he must, handspike in hand, mount the windlass and, in deepest bass, lead the chorus,

        “With a stamp and a go,
        And 'Yo, heave oh!'”

In brief, the “minstrel boy” must have a fitting song for all moods and every occasion. He is an attraction in the carouse on shore, and in the night-watch in calm and storm. Such a treasure we had in our mulatto boat-steerer, Harry Hinton. Brave and faithful, he never shrunk from a duty below or aloft, or a danger in boat or port. He stuck to the Chelsea through good and evil, and was one of the six who remained to drop anchor from our old ship in New London harbor.”

[Davis, William M., Nimrod of the Sea or, The American Whaleman, (New York: Harper & Bros., 1874, pp.29-31)]

[Nantucket Historical Association summary note: Account of voyage; original is Log 354. Used in preparation of William M. Davis "Nimrod of the Sea or The American Whaleman" (Harper 1874)]

Fiction? Non-fiction? "Based on a true story?"