Thanks, Gibb. This gives me the chance to blather on.

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.

As for the halliard shanty, here's my theory:

A sailing vessel large enough to require a crew of at least a dozen or so men is preparing to leave port in the year 1820 or so. One group is heaving anchor at the capstan, singing some song or another that has a chorus. The paractice of singing at the capstan is not universal but is not considered odd or peculiar either.

While one team heaves the anchor, another team is pulling on halliard to raise sail. It is usual for there to be a leader in such a group who calls out something trivial, like "One! Two! Three! Haul!", the sort of cry that no writer would consider to be of the slightest interest.

At some point, the leader of the halliard gang gets tired of "One! Two! Three! Four!" and starts to call out something arbitrary but amusing because it isn't just counting, something like, "Sally Brown, O Sally Brown O!" and everybody hauls at the end.

Because the capstan gang is singing, the leader at the halliards decides at some point to sing too. He sings something like "Sally Brown, O Sally Brown O!" to a simple rising and falling tune, almost the simplest possible. At some point, maybe that day, maybe the next time a yard or sail had to be handled, during a pause for breath between hauls, somebody else decides to chime in with a line like "Way-ay-ay-ay!" Eventually the leader develops his tune a little further and eventually a second refrain gets added.

Just why that should have happened is not clear, but if it hadn't, maybe the halliard shanty would still be thought of as a mere "chant." The four-line structure could have encouraged the development and importation of more or less stable verses as the "chant" became a real "song."

By the end of the voyage, at least one shanty has been composed. The chants of cotton-screwers may have inspired the first shanty or not: they certainly contributed to the practice.

This could easily have happened more than once in a period when more than one gang had to work at once so as to get a big clipper underway. That polygenesis would help explain the rather sudden rise of shantying and the rapid rate at which individual shanties seem to have appeared. An important contributing factor was the singing that was already semi-customary at the capstan. Thus the first halliard shanty developed in the spirit of a singing contest.