Get hold of a copy of Stan Hugills book "Shanties from the Seven Seas"
ISBN 0-913372-70-6
Available from Mystic Seaport Museum, inc.
75 Greenmanville Avenue,
Mystic, CT. 06355.
(priced at $19.95 some years back, & worth at least double)
It contains a wealth of info regarding shanties, their history, and how they were used. Much other interesting stuff as well.
Beg, borrow, or better yet, buy a copy!