From Uboat.net
.....................Surface......Submerged....Dep th
IIA ................13.0kts....... 6.9kts.........150m
IID.................12.7kts........7.4kts......... 150m
VIIB...............17.9kts.........8.0kts......... 220m
VIIC...............17.7kts ........7.6kts ........220m
VIIC/41...........17.7kts .......7.6kts..........250m
IXB................18.2kts.........7.3kts......... 230m
IXC................18.3kts.........7.3kts......... 230m
IXC/40............19.0kts.........7.3kts.........230m
IXD2..............19.2kts..........6.9kts........2 30m
XX1...............15.6kts.........17.2kts........2 80m