What I see that Harwich/Felixtowe area is well covered by AIS reception from those who supply FREE AIS receivers like Marine Traffic, Fleetmon, Shipping Explorer etc.
BTW, if any shipspotter would like to join network and apply for free receiver please contact any of those suppliers.Of course, your area must be attractive(not yet covered by AIS reception).New members are always welcomed especially those living near busy ports,channels or on high altitude above sea level.
Wish you luck.