I had this discussion with someone from a shanty group, Steve. Yes, they were work songs and I would certainly concur that no-one purposely put any harmonies in. However, harmony happens whether it is meant to or not. Get a group of a dozen or so people singing and, whether by design or accident, some will be harmonising. May be because there are some notes they cannot reach. May be because that is what they hear. Could be many other reasons. But he was insisting that shanties should be in pure unison because that is how they were sung. That was probably as they were intended but I doubt that is they way they came out!

Nowt to do with the thread of course but an interesting enough aside I think :-)