Welcome to Subsim.
IIRC (cos doing this from memory) you can remove the Compass/Bearing Overlay by going into the Player Sub folders inside the main SH3 program folder (example \data\Submarine\NSS_Uboat7b) and backup/delete the TGA called NSS_Uboat7b_shp.tga.
This is the overlay file and you will need to do the same for all the player boats.
Best to backup/save them elsewhere, just incase.