Try around AM17, AM18 there is a shallow patch of water there, shows up as a white patch. I've caught more than a few convoys comming through there as they head to the North approch to the channel. Another is the BE 30's for the South approch to the channel. Another convoy route is through DT 20's, 50's and 80's, the Freetown/Liverpool and Freetown/Gibralter route.
If you have a Type IX hang around BB 70's and 80's quad South of Halifax, good convoys there but watch for the air cover, or the Upper CB 10's, 20's and 30's. There is also 2 Passenger liner routes about 35Klm apart that run through the upper CB's comming out of New York. I've caught one liner on the South track and an hour later caught one on the North track.
Good Hunting!