The passenger lists for ships sailing out of Hamburg in the 1800s are available online. Johann Holtorf sailed with a ship called the Steinwärder, which sailed on 3 November 1856. The following is an excerpt from Steinwärder’s passenger list. Johann’s name is listed as Joh. Oldorf, age 28, landmann (farmer) of Bramstedt, Holstein. It is not exactly easy to decipher, but with the eye of faith…

Although the details of the voyage are not visible on this selection, according to the Ancestry records the ship type was “segelschiff” (sailing ship), the accommodation was “ohne angabe” (not specified), the captain was Arens, H. E., the shipping line was Joh. Ces. Godeffroy & Sohn, and the destination was Sydney. The only picture I have been able to find on the internet of the Steinwärder is the following, from the State Library of South Australia, which shows that it was a three masted barque of 320 tons.

There is a fascinating description of conditions on such migrant ships at this website.