Trying to dig up some references to overlapping, to see what's there to be interpreted.

1906. "Sailors' Songs, Collected by Annie G. Gilchrist." Journal of the Folk-Song Society 2(9): 236-249.

Mr. Bolton refused to give me the rest of the words! "Shangadore" is a corruption of "Shenandoah "-the American river of that name. …this well known American chanty, …The tune appears to be of negro
origin; it is at least of negro character…. The tune is a difficult one to bar correctly, from the evident tendency of the chorus (as I understand in chanties generally) to overlap the solo….


1927           Gordon, Robert W. "Folk Songs of America: Work Chanteys." New York Times (16 Jan. 1927).

About boat-rowing songs in Georgia. Gordon notes that the leader sang in tenor, response in lower key. Lines overlapped "with curious effectiveness."

1906    Masefield, John, ed. A Sailor's Garland. London: Macmillan.

Of the chanties proper, the capstan chanties are the most beautiful, the halliard chanties the most commonly heard, and the sheet, tack, and bowline chanties the most ancient. In a capstan chanty the solo man begins with his single line of verse. Before he has spoken the last word of it the other men heaving at the bars break out with the first chorus. Immediately before the chorus has come to an end the solo man repeats his line of verse, to be interrupted at the last word by the second chorus, which is generally considerably longer than the first.