Just to add to this thread, for comparison, the part of one of James Runciman's stories where a similar shanty is claimed--

In the story "An Old Pirate," published 1885, one of the characters "hummed the shanty,"

So where they have gone to, there's no one can tell—
   Brandy and gin and a bottle of rum;
But I think we shall meet the poor devils in hell,
   Brandy and gin and a bottle of rum.
...

We went over the bar on the 13th of May,
   Brandy and gin and a bottle of rum;
The Galloper jumped, and the gale came away,
   Oh ! brandy and gin and a bottle of rum.

After this, the narrator states:

"I had heard the wicked shanty on board a collier brig, as it happened, but my version was corrupt. The gruesome song which Mr. Louis Stevenson lately printed is also corrupt. In fact, Mr. Stevenson's verse is so artistically horrible that I rather fancy he composed it himself."

Although the solo verses of both these versions sound contrived to me, I could envision the chorus as representing a shanty that once existed. This is just my imagination, albeit based on some knowledge of chanty forms -- but I think it sounds like a shanty for the old fashioned spoke windlass. The "heave" would come, as I envision it, on the second "ho" and on "rum." (That is as opposed to a halyard or the brake windlass style, where the pull/heave would be on "Yo" and "bottle." If such were an actual shanty from the hypothetical old days (late 18th - early 19th century), I'd expect the solo parts to be more of a sort of incidental gibberish (which is why these versions sound too "composed" IMO).