I definitely have come across the term 'sweet ship' in reference to a ship not possessing the normal bilge stink of sailing vessels, due to carriage of aromatic cargoes. Sorry I can't look up the reference just now - deep into research of revolutionay period French navy tonight!

edit: this seems a similar example to what I've encountered in a novel:

She was a sweet ship; and the air below, though stuffy, had no taste of bilge in it. ...

http://www.blackmask.com/thatway/books171c/whitwo.htm