I've told this before, but it fits in here. Many years ago when Stan Hugill was recording what became Shanties of the Seven Seas, in Cecil Sharp House, he needed a chorus, and I got drafted in, because I was a regular at a neighbouring folk club.

Anyway, he wanted us to be authentic and it was a stereo recording (which was a bit of a novelty), so for the capstan shanties he had us walk round in a circle, as if we were pushing the capstan round; and for the anchor hauling we were lined up along with a (electric) cable and so forth.

The point is, the rhythm of a shanty comes from the work being done. And many of the shanties would have been used for different type of work at different times, and the rhythm would have varied accordingly.

And yet again there are some shanties that would also have been sung away from work, as forebitters, or in the pub ashore. I imagine when they sang them there they'd probably have sung them a bit differently from when they were working, and very likely faster, so perhaps singing them faster in a folk setting isn't as untraditional as all that.