about the "big circle" look here
http://www.uboat.net/articles/id/51
its basicly just a radio direction finder for the uboats (dont think it works in SH3 though)
and for the deck gun try to aim a little bit below the water line (shell will still "fly" a little under water) it will cause a little bit more flodding
and "realistic ship sinking times" just makes ship sinking times longer
and i belive you have to stay in visual to get the renown
hope this helps
