True sea shanties would never be heard onshore or on the off time. They are the work songs of the sailing ship, waulking songs are work songs as is prison work songs, railroad songs & cowboy songs but they're not shanties. The only places I've heard (so this is IMHO) of shanties outside of this realm would be in the Georgia Sea Islands where songs for rowing & cargo loading were included in this & in the West Indies & neighoring islands where they included again rowing songs as well as house moving songs. Sea songs sung for the sailors enjoyment & not used for work were called forebitters (of course many shanties could be adapted to fit many work situations). A shantyman was said to be as good as 10 men on a line & though he may not have been paid outright his position would be a position of far better than most any other member of the crew.
Barry