The answer is very simple.
You need a Nvidia GTX 470, ATI 6850
or better.
With these Cards, you should be able to play fluently (more than 24 FPS) at a resolution of 1680 x 1050 with 4x AA and 16x AF. Assuming you also have a 2 or 4 core CPU with more than 3 GHz and enough memory.
It goes also with some older graphics cards like the GTX 275, GTX 285, ATI 5850/ 5870. But you must take a look at the Price, these cards are also not cheap and have the older technology.
I know, thats very heavy, but this is the standard for modern ship simulators.
If your system is strong enough, you can optimized the graphics with the driver software of the graphic card.
For ATI cards you can take a look here:
http://80.95.161.114/shipsim/forum/index.php/topic,19579.msg266905.html#msg266905
Regards
Thor