But, Gibb, would the song really urge people to "knock" cargo into the hold? Since "knocking" things usually involves a stick or a fist, what kind of cargo would be light enough and/or rigid enough to be "knocked" into a hold so routinely that it would be immortalized in song?

Particularly when "man" makes perfect sense, and the chantey has nothing to with cargo, including stowing it.

And since working sailors could easily inmagine real people, like the bosun, captain, mate, and that moll's fancy man, that they'd just love to knock down. (And, in one version, "kick him around.")

"Blow the man down" means to knock somebody over with a gale-force blow.

But as I wind up saying all too often, people will read into words whatever they want. Perhaps a red stoplight really means "go," because red is an vivid, energizing, empowering color, while green means relax and think of springtime. ZZZZzzzzzzz.

You're ubndoubtedly right about the alleged connection between "Blow the Man Down" and the Black Ball Line being exaggerated. But skippers on rival lines might have discouraged use of the "Black Ball" version aboard their vessels.

Sure, the Black Ball version by definition must have been "especially associated with the Black Ball Line," but the number of other versions shows that "Blow the Man Down" in general was not.