Also, as to the Channel and the grid NW of the coast of Cornwall...
If it's 1939 why not go for it, the channel is survivable in 1939 if not exactly easy, and the approaches to the bristol channel are definitely a great hunting ground if you like sinking tankers, odds are however that if you pass the strait of Dover you won't even get as far as the Atlantic on account of having run out of eels... and then you'll have to run the channel again on the way back..
oh well that's life in the Ubootwaffe
P.S. There's a brief guide to running the channel in the GWX manual
