Easy mod, actually.This is how you to do it. First, you need the Mini Tweaker program. Also, be sure to download my sub.sim Tweak Files.
If you don't have SH3 intalled, you need to create empty folder directories like this:
C:\Program Files\Ubisoft\SilentHunterIII\data\Submarine\
Now, copy all of you submarine files from SH4 into this new, empty SH3 submarine directory.
Next, open the Mini Tweaker program and look for the submarine .sim files in each sub folder located in your SH3 directory.
Minelevation and
Maxelevation settings adjust how many degrees the bow and stern move up and down. Also,
gc_height adjusts the center of gravity... meaning how much the sub will rock back and forth in the waves.
Important- when modding, never leave backup files in your SH4 Library directories. If you do, the new, modded files will not be recognized by the game and the changes will not show. You must move any backup files out of the SH4 Library folder. Backups in the SH3 Library folder doesn't matter.
Good luck.