Ok so it seems mine isnt broken then, it just doesnt add many ships. I do occasionally see ships in the open ocean or just typically a long way from land but they are very occasional even in some of the major shipping areas I have flown so far.
In the end I have since added the free mod "Global AI Ship Traffic" from flightsim.to and now I can see ships everywhere. Flying between dover/calais on my last flight I could see about 5 ships which would be pretty typical of that area. It seems both the free mod and the Seafront/Orbx pack work ok together so Im going to stick with the Orbx addon to see if it improves but I will be more hesitant with future purchases I think after this one and a few others recently that haven't been as good as I hoped.