No-one on this thread [I haven't checked out the other yet] has mentioned any possible drift in from "See her running thru the water [refrain] I wish I was in bed with the captain's daughter", which occurs in other shanties, e.g. Hob-A-Derry-Dando; and might well have floated in from there, or been regarded as one of those commonplaces for the nightingale to insert when he ran out of ideas on a long job.

~Michael~