"Roll" in shanties is often the seaman's pronunciation of "row": insertion of an 'l' for a vowel was quite common practice to provide an elision, so that 'row along' could become 'roll along', and could spill over where next word did not begin with a vowel. Forget whose suggestion I once came across that this was a shanty for rowing ashore on the liberty boat, which would make sense of the rest of the litany of what 'wouldn't do us any harm', i.e. while ashore, culminating with the 'night with a whore'. The ad hoc ref to the boat as a 'chariot' could be a spill over from the song's supposed spiritual origins [see above], emphasising the agreeably 'holy' nature of a brief spell ashore in the men's industrious lives.

This is probably, I am only too conscious, one of those over-elaborate 'folk derivations' which we all know we should beware of [like brass trays called 'monkeys' & cannon balls!]; but one that nevertheless appeals to me as a 'just maybe'.

~M~