convoy interception training mission - HELP.

[misfitdreamer]

hi all,
i'm still very early in understanding the full mechanics of operating a fleet boat.. and before i set out into campaign or single missions i want to make sure my skills are at least somewhat honed. i've been therefore trying to tutorial missions over and over again and my first success was learning how to manually target (yay! :p) but now i'm quite confused by the convoy interception. i'm confused as how to determine range and bearing of radar and sonar contacts.. and more importantly - how to remain undetected. it seems i'll travel submerged for quite a bit and then when i rise to periscope depth to visually check on the convoy.. the escorts have already picked up on a whiff of me and the convoy has started zigzagging or have started running around crazy.

i'm stumped. i need advice.. what should i do for this mission?
anything would be great at all.

if it helps, for the time being i'm playing on low realism settings.. the only one's on being disabled free cam and manual targetting.