Sea shanty collector Joanna Colcord in Songs of American Sailormen (1938), pp. 99-100, adds this speculation to the above discussion with regard to "Clear the Track":

"The probability is that some Irish sailor, ashore on liberty in Mobile, sang "Shule Agra" in a water-front saloon. It pleased the ear of the Negroes hanging about outside; and the next day they sang what they could remember while screwing home the great bales of cotton in some Liverpool ship's hold. Negro fashion, they put in the rattling succession of sixteenth notes, and added the "bullgine" for good measure. The crew of the ship heard and liked it, perhaps without recognizing its origin; and took it back with them to Liverpool. There the crew of the Margaret Evans, a well-known American packet ship, lying in the Clarence or the Waterloo Dock, picked it up and fitted in the name of their ship, and took it back to New York, with Liza Lee and the bullgine still in close conjunction with the low-back car, to the puzzlement of future folk-lorists!"

Fun!

Cheerily,
Charley Noble