[Krupp]

[/quote]
Setting your speed manually to 2 knots will give you about 12 hours under warter, that should be enough IMHO.[/quote]


12 hours is not even remotely enough. Here's some stats from original diagram USN Fleet submarines manualthingie.

Maximum Time Submerged and Cruising Range vs. Submerged Speed Knots

knots--miles(peace-time)-- miles (war-time) --hours(peace-time) -hours(war-time)
2 ------73 --------------100-110 ------------36 ----------------55
3 ------69 --------------100-105 ------------24 ----------------38
4 ------55 --------------83 -----------------14 -----------------24
5 ------40 --------------64 ------------------8.5 ---------------14.5
6 ------30 --------------48 ------------------5 -----------------9
7 ------20 --------------31 -----------------2.6 ----------------4.8
8 ------14 --------------23 -----------------1.6 ----------------2.6
9 ------9 ---------------15 ------------------1 -----------------1.5
10 -----10 --------------X--------------------X-----------------X


In game, the Porpoise class can do submerged travel (with 3 knots) about 33 nautical miles in 11.5 hours. After that the recharging took only 1 hour (from 9% to 100% battery charge).

Something is biased, and without TT Tweaker, we can't adjust those I guess.