I have just returned from one of my photo tours of NW Europe (see trip report later) but for reasons I will not go into here, I went out Dover-Calais rather than my usual Dover-Dunkirque.
The "Cote de" class of ship on this route are useless for cross Channel photography!
The stern deck is either obstructed by the foot passenger loading ports or has perspex type sheeting (presumably for wind protection) preventing any decent shots. In addition, there are no seats and although the next deck up appears to be unobstructed, it is reserved for truck drivers only and the stairs padlocked.
Returning from Dunkirque on the "Seaways" class was far better.