Get III loaded then download GWX 3.0 its the standard!

Realism out the yazoo.
Then go to SHIII mods section and get real life boats and debris mod that adds men in lifeboats paddling away from ships you sunk! Then add the Water effects mod that adds water running down the side of your U-boat.
They are both great and I play both regularly although GWX 3.0 is hard to beat.