appended you will find the detail of the first kilometers of the donaukanal.
You will see at schwedenplatz the twin city liner, now in winter leaving on saturday, sunday and holiday at 10:00 and returning at 18:30. Be carefull, the twin is driving fast!
Here the map: http://maps.google.at/maps?q=schwedenplatz&hl=de&ll=48.211877,16.379414&spn=0.005555,0.012274&sll=48.116835,13.87012&sspn=2.849383,6.28418&t=h&hnear=Schwedenplatz&z=17
Also take care of the fast streaming ( max 6-8km/h ) and always paddle with the stream.