Doh
I solved my own problem.
In case anybody else has the same one, the tga file which makes up the bearing grid, which you have to name to match the different submarine types has a double underscore in it __ I didn't notice, the game files only have one.
I feel like one of those people who ring tech support, then actually find out that they really didn't plug in the computer
Oh well, my manual targeting can go on apace now
Cheers
Varro