In his Feb 6 email, San Francisco Chanteyranger Peter Kasin says this:

If you are confused by the two spellings, "chantey/chanteys" is the U.S. spelling. "Shanty/Shanties" is the UK/Ireland spelling, as well as in a number of other countries.

Don't know if that's true, but that's what Peter says - and he's the only formerly professional chanteyranger I know.