SF Ammonia is a steam powered railway ferry on Tinnsjø that connected Rjukanbanen with Tinnosbanen, Norway. The ferry was one of the four railway ferries on Tinnsjø that was used by Norsk Hydro to transport chemicals from Rjukan to the port in Skien. The ferry is one of four remaining steam powered railway ferry in the world, and can still be seen docked at Mæl.