Derpy: '"Blow the man down" refers to taking down the main sail of a ship.'

As much as I would like to agree with Derpy, and even suggest the original words were or meant Strike the Main(sail)Down. It doesn't hold up to a sailor's scrutiny.. "Blow the Man Down" is a halyard shanty; the purpose of which is to raise sail. "Blow" is a shout which would achieve the greatest exertion at a single point in time. Qi or Ki in oriental parlance.

I believe Blowing the man down has two referents. The song originally was a forebitter, not a shanty at all. The original refers to Ratcliffe Road or in most versions Paradise Street. The first destination of most sailors in port, where as often as not the "Flash Packets" would relieve Jack Tar of his hard earned pay by fair means or foul, effectively striking the sailor down.

In a later period when the packet ships were competing with steam the harsh discipline exacted by officers in striking men down is doubtless the referent. The Black Ball Line being particularly noted for this type of behavior.

Interestingly some earlier posts in this thread refer to Mickey Finn. Mickey Finn was a legendary roustabout and riverboatman cited in "Davy Crockett's Almanack" published in the 1830s. Packetboat service started on the Erie Canal and western rivers around 1825. The one story I specifically recall about Mickey Finn is "Trimming a Darkies Heal", A particularly nasty bit of work about a very evil fellow.