I have some problems during manual targetting. I do use WO's help when I'm on the surface, but since it happened only once or twice, I have to do all the calculating from PD, so WO is unavailable

I have problems with calculating speed. Everytime I try it gives me or a to low speed or unbelivebal high speeds. I think it is due to my own speed. Is there a good method?
And from what distance do you usually launch the torps?
I have a ton of questions, but these problems are hampering my game experience!
Thank you a lot for the patience and the help.