Great to have a lot of voices here.

A couple things I encourage here:

1) Though I am very often guilty of "vagueing up" my statements, particularly when I'm unsure... let's to to specify time period when we talk about things, when possible. A couple decades in either direction could make a huge difference (e.g., a couple decades ago, I wasn't using the Internet). I personally I looking for "Ground Zero" of what I think was a "new" phenomenon --post-Cheerly Man. Perhaps it was not, but still I've got to "zoom in" to see.

2) Let's use previous writers' thoughts as springboards or reference points, but not accept their assumptions. Let the evidence speak fresh.

mikesamwild--
By "Yellow Girls" do you mean the shanty AKA "Doodle Let Me Go"? That may be something to pursue.

And I am sure it was a fusion, but then again, what is not? The tunes may very well be of Irish derivation. The challenge will be distinguishing what precedents are most relevant to the historical context. The melodic influences on, say Jamaican stevedores, may have included Irish polkas, since what is "Jamaican culture" --or any culture-- but a fusion of past influences?   This influences become relevant when they suggest something of significance at that historical moment.

In my working sketch, the most important aspect of it all at this "moment" was a paradigm for singing while working. The non-Black commenters have remarked on Black work-singing as if it were a practice distinct from their own. My contention is that there was something culturally remarkable about African-American work-song practice. One aspect, for example, was the feature whereby a gang of workers might have an individual who *only* sings (and gets paid for it!). Another aspect is the specific *form* of these songs.

So I've an open bias towards looking to African-American work-singing for some answers, at this point. This does not mean I think "chanteys are African"; on the contrary, I think they are fusion. However, my hypothesis is that the "new phenomenon" of "chanties" was based in what at the time was a work-song practice of the African-American community.

Looking for antecedents --in a different world than The Complaynt of Scotland -- we have for example the account (published 1800) of Scotsman Mungo Park, who visited the area of Africa that is now Mali in the 1790s. He observed of the people there that, "They lightened their labour by songs, one of which was composed extempore, for I myself was the subject of it."

That was in Africa. Here's an observation from the New World a decade later, on the island of Martinique, in BELL'S COURT AND FASHIONABLE MAGAZINE, May 1806:

"The negroes have a different air and words for every kind of labour; sometimes they sing, and their motions, even while cultivating the ground, keep time to the music."