If it must not be Stade, I recommend Altenbruch near Cuxhaven. Here you can also see the ships coming from the Ciel Canal or going there. That is far more than from the Ciel Canal to Hamburg. Cuxhaven is easy to reach by train. Altenbruch has also a train station but I do not know whether the train stops there. In Altenbruch you have the Hotel Deutsches Haus (http://www.deutsches-haus-altenbruch.de
). From there it is about 1.5 km to the river Elbe. There is the buoy bath. There are some benches to sit. On the dike is a bistro. The shipping channel is only a few meters away. From there you can see very early the ships at a distance.
I wish you many good photos