I have read alot of uboat books. My favorite one was
Iron Coffins.
As far as torpedo dept; I set my torps 1 meter from ships keel depth. If weather is rough I run the torpedo a bit shallower.
I do know snorkel is available if you use TDWs UI mod. Not sure about torpedoes since I am only in 41. I did access to a new electric torpedo not to long ago though.