So I successfully left the port..
I also was monitoring Vorpostenboot strugling to get out of the harbour over my binocs. On his third attempt he managed to escape the wall but then he found another trouble in his path:
In this picture he was probably brushing a net with his starboard side untill he sank himself..
(He is just behind that Hansa freighter on the picture)This event surely explains why there is no escorting vessel around this harbour and why we need mines/net map updated..