Firing blind

[Zorgl]

Hello everybody. I play at full realism, except that when there is contact it is automatically located on the map. And one thing i'm wondering, is ; how can I lock a target without using the periscope ? I'ma kind of a coward and don't like having my periscope up. I can enter the AoB and speed (I calculate manually) in the TDC, but I never get the estimation on my tactical map. I believe it's because I can't enter the range. Help ?

Also, what's the use of TBT ? Byt the time you get in range of seeing an enemy ship with it, it can see you as well, with the submarine being above water !