I think that your family stories, as family stories often do, are probably doing you a disservice. Firstly your grandfather could not have come from anywhere in the SS America in the 20s or at least the early 30s, simply because she was not built until the late 30s, owned by the United States Lines. In addition she was on the regular passenger run from Southampton to New York and certainly never went anywhere near Russia, although she was requisitioned during WW2 and then went to a lot of other places as a troop ship. She returned to regular passenger service in 1945 and was finally sold to the Chandris Lines in the late 60s and renamed the S.S. Australis.

Your grandfather also never fled from behind the "Iron Curtain" in the 20s or 30s. This was an phrase coined by Winston Churchill in a speech, given in Fulton, Missouri if I remember rightly, in 1946/47 to describe the spread of Communism in Eastern Europe. He said (may not have the words exactly right, but close)"An iron curtain has come down across Europe from the Baltic to the Balkans ..."

I would suggest that your first line could be to find out which of any languages was his mother-tongue - although it is true there were quite a lot of German speaking Russians in the Ukraine. Assuming he was a naturalised US citizen his naturalisation papers could have more detail, marriage certificate? Your father's birth certificate? You indicate that your father is still alive, perhaps he could give a few more pointers. I hope this might help but I honestly think you are very unlikely to get much help unless you can narrow your search down a bit. Good luck.