Here's another nice source that mentions riverboat songs that may be connected wih our chanties. These were observed in 1853 by Frederick Law Olmsted, in his A JOURNEY IN THE SEABOARD SLAVE STATES.

While going up the Red River to Shreveport, LA, he jotted down these. The Black boat-hands sang, (p608 ff.)

"Ye see dem boat way dah ahead.
CH: Oahoiohieu
De San Charles is arter 'em, dey mus go behine
CH: Oahoiohieu"
[etc -- several more incidental verses]

This song ALSO looks to me like "The Sailor Fireman." It has the right rhythm, and the chorus is close enough. The chorus also reminds me of another river song, "Lindy Lowe", and playing with the vowels in the word "Ohio."

Another song quoted seems to have a phrase similar to "Jonny Come Down to Hilo":

"Ime gwine away to-morrow.
   Oh, John, come down in de holler
Ime gwine away to marry
    Oh, John, come down in de holler"
[etc]

Several verse lyrics are reminiscent of "Shallow Brown".

Elsewhere in the book (pg 26) the author describes a funeral service in which, as people were filling in the grave, an "old negro" "raised a hymn which soon became a confused chant" in call and response fashion "in the manner of sailors heaving at the windlass."
   
On pg 394 there's some yodeling and "rolling the cotton down" of a sort!