Sciencegeek is right, you have to hear the hitches to get a clear idea. The melismata that Lloyd referred to are often indicated in Sharp's transcriptions, but these are not what Hugill usually called "hitches." "Yodeling" may be the best word for one kind of hitch, usually at the beginning of a solo (as in GregB's example), but the "yodel" is usually just a grace note or two, not tuneful like actual yodeling. The other kind of hitch is a falsetto upturn at the end of a word, usually at the end of a solo line.

I think that singers trying to imitate Stan sometimes use more hitches than he ever did, but it was undoubtedly an individual shantyman's preference as to when and where. Stan wrote that the hitches usually appeared in the solos only.

Without using the word "hitches," a writer in the American magazine Harper's Monthly unmistakably mentioned them as a shanty characteristic as far back as the 1880s.