Well, it did make a difference. Sailed my Tambor around the west cape of Australia and CTD'd. Loaded up again and sailed almost to my destination (N. of P.I.), encountered fishing boats and sampans, sinking them with my deck gun. Encountered a split freighter and exchanged surface fire (taking some damage) in the process of closing in at periscope depth to sink it and ... CTD.
Well, that's better than before.
Now, about the officer's quarters. I was told that I had the wrong version of that, as well. I have version 1.39. I thought that was the latest. I downloaded the compatibility patch, as suggested but am holding off adding the 1.39 plus patch until I test FOTRSU some more.
Still ... progress is progress.