If you want to photograph ships on the move, head to the eastern end of town to the beach.
From there, walk along the breakwater to the end which forms part of the harbour entrance.
From here, you can watch them coming and going in and out of the port and you will also catch them coming out of the bay, approaching the port.
On Google maps, look for Bd Albert 1er and Bd Clemenceau.
Better yet, put this into Google maps:
"office de tourisme de l'agglomeration Havraise"
From there, you need to walk out on the long thin wall that points SSW.