Hey there, Gaby! I hope you're doing well and I hope that you'll see this at some point.
I was able to find a passenger registry of a Heinz Gercke from Germany to Australia between 1897 and 1963. Unfortunately, Ancestry.com requires a payment to see the list, but they do offer a free trial you could use to see it. You can follow this link to see what I found (http://tinyurl.com/hl89duy).
Also on Ancestry.com, I found phone registries for Heinz Gercke in Berlin and Hamburg, but these I'm less sure could be your father. (http://tinyurl.com/zy7xbvv)