From the Memoirs of Elkanah Watson, pub. 1856. The author relates a scene from 1777 (!) in South Carolina.

As evening closed in, we embarked in a good ferry-boat, manned by four jolly, well-fed negroes, to cross Winyaw Bay, a distance of four miles. The evening was serene, the stars shone brightly, and the poor fellows amused us, the whole way, by singing their plaintive African songs, in cadence with the oars. We reached Georgetown in the evening.

"plaintive" again :)

Anyway, this is interesting to note how at the earlier date they were "African" songs (presumably not in English language?). See upthread for Pinckard's 1790s expedition and the rowing song chorus that had seemingly African-dialect words mixed with English. Later it is all English. What I'm hoping to establish is the idea that the style of rowing songs current in parts of West Africa was maintained among African-American rowers in the New World. All this is by way of setting up ONE ASPECT of the work-song context from which "chanties" may have emerged: distinctly African-styled practice of singing while rowing. This is not to say that the melodies, for example, were necessarily maintained "from Africa," but that the paradigm and form persisted.