Consider Roger Abraham's book, "Deep the Water, Shallow the Shore," in which he discusses West Indian chanteying. Among the points he makes is that a) there were work chants used for for moving houses [shanties] from place to place and b) the origin of the word goes back to a period when spelling was not regularized.

Bear in mind that the English language has been described as "two cultures divided by a common language." The American group generally spells it as "Chantey" [except for Charley Noble]and the English group
tends to spell it as "shanty" with variations in both groups according to the user's inclinations.