This is a reasonably slavish copy of Peter Bellamy’s rendering of this song, which I think was based fairly closely on how Sam Larner sang it. It’s also known as “Pretty Polly” and “The Cruel Ship’s Carpenter”, but Sam Larner called it “the ghost song”, so I’m sticking to that. It’s an extraordinary tune, which took a fair bit of learning.
The lyrics are unusual, particularly in the English tradition; it’s a murder ballad (not a particularly thriving genre on this side of the Atlantic), but one with a supernatural ending. The belief that a ship could not make way if there was a murderer on board was widely held – see also “William Glenn” – and in any case made a good plot element. The apparition of Polly at the end seems quite corporeal; I get the impression that the idea of ghosts as insubstantial phantasms is quite a modern one, perhaps only dating back to the rise of spiritualism. To judge from songs like the Wife of Usher’s Well or the Suffolk Miracle, pre-modern ghosts might appear and disappear unpredictably, but they would seem quite solidly human in between times.