Help with radar escort tactics on full realism. (SH3 GWX)

[predattak]

So.. it's March 1941 and everybody and their mother has radar.
At first i thought..well it's march.. maybe only some convoys have it but no, all convoys have at least one radar escort.(in most cases 3 out of 4 escorts have it)
They see me through the most horrible weather out there in the middle of the night giant storm (full sh*t show) they come at me perfectly and hunt me down. Every time.
I have to keep at least 18 Km range from the convoys if i don't want to be seen.

How do i even approach convoys without being detected?
How do i get an accurate course of the convoy if i can't go close enough to at least spot the damn smokes? 4 bearing method doesn't give accurate results because the convoy sounds are everywhere.
Tactics would be great since i'm quite new to this.
The more the better!