"There are countless versions of Blow the Man Down. The one here is from the Burl Ives Songbook and tells of the Blackball Line. The Black Ball Line was founded by a group of Quakers in 1818. It was the first line to take passengers on a regular basis, sailing from New York, Boston and Philadelphia on the first and sixteenth of each month. The Blackball flag was a crimson swallow-tail flag with a black ball."

Lost the site. But this is the pertinent part.