From my own time in the Merchant Navy and my contact with a real shantyman (Bless you, Bert Gray, where ever you are) I recall, his contention was that "Drunken Sailor" was a virtuoso piece for shantymen, always started with a few standard verses then used as a platform to show off the shantymans skill at improvising verses, especialy about fellow crew mwmbers and with lots of "local colour" and in jokes, and in his (Bert's)honour, on the rare ocassions I sing it, I have tried to do the same.