PPK:
If you zoom out far enough you should see your own icon. But that means your drawing accuracy might become a problem. Well, you ought to plot for longer than 3m15sec anyway and average the plots.
But if that isn't enough, you can allways drop a waypoint on the map and subsequently ignore it. Just set your own course with the compass dial and the waypoint will still be there... with a green line pointing to some spot. That's where you are now. (and you can confirm that by pressing ctrl-leftclick, then the map pans to get your icon under the cursor.)
Your suggestion added as EDIT is indeed valid. That would make a relative motion plot (your sub stays in the center of the drawingcircle, while you plot target range on true-bearing to target). But that 'speed of relative motion' and 'direction of relative motion' needs to be vector added to your own speed vector to become the absolute target speed and course. It's a bit more complicated than how it is done in Paul Wazzoo Wassermans or Dantenoc's 'The Hunt' tutorial but definatly historical accurate. Since they didn't have a moving map GPS plottes in the uboats. iirc Don1reed wrote a small tutorial on this once, but becarefull, he made an error with the speed scales. Also his pictures are gone. But maybe it's still of some use to you:
http://www.subsim.com/radioroom/show...euvering+board
When in doubt, consult chapter 6 of this book about radarplotting and the maneuvering board.:
http://www.nga.mil/portal/site/marit...c24fd73927a759