Well T-tone, I think it is a work song used by sailors. The earliest records of this practice.
1. 1066 one of the monks with duke william as they left Normandy wrote that the sailors sang chants as they raised the sails.
The Normans were of Viking origin (Norse men)
2. an earlier instance c400AD another monk (could be Bead) wrote of saxon sailors singing chants as they hauled ropes and nets.