Departed Kiel and used river to Brunsbüttel, but got CTD when approaching the first city, Rendsburg, near the island.
I have a "safe-ish" loadable save on the river a few KM past the gate into the river, but got a CTD again at the same location.
In both cases, my max TC was 16x.
EDIT:
Used an older save just outside the Kiel Pen, and made it though the river past Brunsbüttel.
I'd guess the other save wasn't safe after all...
-Ed