A cappella renditions of songs sometime do not fall into strict meter. I am not that familiar with chanties, but I can see where they could be sung without strict meter when performing work chores like the windlass. The YouTube reference presented excellent variations of the song.

The versions of Shenandoah I have heard all seem to be metered in 4/4 time, especially when accompanied by instruments. When multiple instruments are playing, it is almost imperative that a strict meter is followed.

There are many examples of songs, like ‘Barbara Allen’ that can be performed in either 3/4 or 4/4 meter. This is totally up to the performer.