Hello Bugsy. I read your last post and thought the links below may help you in what you are looking for.
http://www.wikihow.com/Calculate-the...to-the-Horizon
http://www.subsim.com/radioroom/showthread.php?t=229368
This link above involves a discussion by fellow subsim members maillemaker and TheBerbster on target motion anaysis and I think you may find it useful.
Further, TheBerbster also posted an in depth analysis on how to properly perform an attack in the post and link below. The link includes a video which is also useful. The mast height is important here in setting up your attack. He is using Silent Hunter 5 as a basis, however, the targeting applies to the SH series and any other Sim for that matter. The people who put the SH series and other sims wanted the sims to be as realistic as possible. You can always scale back the realism factor while you learn as well.
http://www.subsim.com/radioroom/show...&postcount=108
I hope this helps you Bugsy. It just takes some practice. It gives you an idea of how difficult it was for submarine commanders to plot an attack. If facing inclement weather, it became even harder.
Enjoy your Sims.