Ooh, this is fun! -- So, we start off, not with the nitty-gritty evidence, but with some sketches of how we might imagine it all happening. I am in total agreement with Lighter's opening statement,

The real mystery of the rise of shantying is probably the invention of the halliard shanty. Any song could be sung at the capstan, and the short-haul and bunt shanties could easily have developed from a single chanted line followed by a single syllable indicating the pull. Such "songs" would not have been noted by writers because they were just one trivial line repeated no more than once or twice.

and with some of what immediately follows. However, here is my imagined scenario of the rest.

First, I'd push it forward into at least the 1830s. There may be evidence I al overlooking that says it would have had to have been earlier. However, I want to argue that that may have been reflecting some of the earlier work-singing ("cheerly man" era, during which, yes, maybe a "Sally Brown" chant had also come into use). In my scenario, it was an *adoption* of chanties, followed of course by further development -- as opposed to an initial development. I don't think the halyard chantey was invented so much as revolutionized by a new method.

In my scene, I envision a small crew in the 1830s, one with a Black watch.   This was a high point for African-Americans in the merchant service; after the Civil War, their numbers had greatly declined. When confronted with the halyard hoisting, the hands found it only natural to raise a song. On shore, these men would never have done labour without a song, which was as much an inseparable tool of work as anything else. In light of the constant labour experience through slavery, work had developed in a way where pacing and coordinated exertion were particularly important. Men were familiar with the technique of working in gangs, as in the cotton-screwing gangs, and they knew with their familiar method they could make short work of this task.

One man, perhaps an ex-cotton hoosier "chantyman," called out, "Stowmy's gawn, that good ol' man...!" To which the others instinctively responded, "WAY storma-LONG john!," giving two coordinated pulls, steadily. The chantyman called "Oh Stowmy's gawrn, that good ol' man!" And again they pulled, "WAY hey mister STORMalong, john."

It quickly came apparent that this was a superior method for raising halyards, and the many previously created songs that fit this style of work -- whether from rowing, cotton-screwing, or loading up steamboat furnaces -- were called into play.