Well then, I can only explain what to do then.
Open the individual Data\Submarine\NSS_Uboat{XX}\NSS_Uboat{XX}.sim with SH3ditor and change the following;
IMPORTANT!! First create a backup of the .sim file you're about to edit!
6: unit_Submarine -> obj_Hydro -> Debug
Mass needs to be 0,1 lower than Surface Displacement
gc_height = variable** (2,5 works for all subs but is particularly ideal for VII)
This setting affects side-rolling, so it doesn't feel as if the submarine is on rails. Higher number means more rolling. A good rule of thumb is to set this close to (Surface Draught /2). That is Surface Draught divided by two, rounded up to nearest 10th.
6: unit_Submarine -> obj_Hydro -> Debug -> Surfaced
Draught needs to be increased by 0,3 (type II, VII and XXI) and 0,2 (type IX)
6: unit_Submarine -> obj_Hydro -> Debug -> Surfaced -> Drag
UD=0,25 (0,20 for a "light" version)
Do this for all the playable submarines, and the fix is complete. Alternatively only mod the ones you're going to use, like I would if I weren't releasing it for download.