Type VIIA decks awash / exhaust?

[IonicRipper]

I noticed the Type VIIA switches to electric motors when i go decks awash but VIIB and above sticks to diesel motors until i go deeper.
Does it have something to do with exhaust location? It looks like the VIIA's exhaust port is on the side of the hull (unless im mistaken) but not the type VIIB/C's...

[Subnuts]

The real-life Type VIIAs actually had diesel exhausts about a foot higher than the later model VIIs. :confused:

[Commander Mysenses]

Try both boats in the same sea state, to rule out the effect of swell.