Honestly, if you’re a such a fan of real navigation for U-Boats, give you a favor and buy SH5 to install TWOS!
This is the only one wich gives you the real taste of real navigation.
TDW made a hell of a job there
And Vecko finalized the mod to make it CTD free.
I love SH3, but SH5 is far superior in that matter (real navigation)