Irishenglish,

I went straight to the source, and here's what Stan Hugill writes in "Shanties from the Seven Seas".

"The older Packet ship words were: Away you Santi, my dear honey... or Away you Santi, my dear Annie... Sometimes too one would hear 'Away you Johnnie, my dear honey' or 'my fair man' (Bullen), but in the main 'Santi' was sung. Now no one as ever given a real reason, or meaning, for this word; it just appears to be a meaningless name of some sort. I thought so too, until I came across a version giving 'Away you Santa, my dear Anna' and the explanation become clear – the mysterious 'Santi' or 'Santa' being nothing more than the two first syllables of our friend 'Santi-anna' or 'Santa-anna' or, as it was usually written, 'Santiana'!"

Santiana is another chantey, the subject of which is the 19th-century Mexican general Santa Aña. So, according to the author of the chantey bible, Santi is a mustachioed Mexican military man.

Jerry