Realistically, what did rigging for silent running do?

[Erich dem Roten]

I mean realistically as in what did U-Boats do differently that meant they were rigged for silent running. I know they would stop any sort of work that made excess noise, like projects going on in a workshop for instance. But short of that, was there really anything else to it?

I ask because when I go silent in SH3 nothing seems to change other than the fact that pumps/repairs (i.e. banging hammers and wrenches), and torpedo loading are all put on hold.