Sea shanties used to have a rhythm appropriate to the work being undertaken while they were sung. Then the "slowing down to lethargy" effect took over ... (I once sang "Lowlands away" at the English National Festival in the company of Stan Hugill and he said it was OK until I slowed down on the last line).

But on the other hand, John Prentice does an interestingly slow and haunting version of "The leaving of Liverpool"