Extending the range

[Leandros]

Reading one of Friedrich Ruge's (German vice-admiral) books recently I came upon an interesting subject. I am not sure if it has been mentioned here. To increase the range on their long-range missions a new technique was introduced. They would cruise with diesel propulsion on one engine and the other on electric, the batteries simultaneously being constantly charged by the one engine in operation. For some reason the electric engine seemed to be more efficient than the diesel one.

As we know this cannot be simulated in SHIII. That said, I feel the operation of the engines, and internal technical equipment, is what is lacking most to be truly realistic. This is one aspect that should be corrected in SH5. For example, the engines can be driven on flank days on end. Surely not an option in those times. Or for that matter going flank in extremely heavy weather for long periods.

[Randomizer]

It is my understanding that this is similar to the configuration finally settled on for snorkelling except that the engine connected to the prop could also put a trickle charge into the batteries as well. Note that the more sophisticated US Fleet Boats used the electric motors for all propulsion, surfaced and submerged and they possessed excellent range.

[Iranon]

Interesting, although I don't quite get it. Afaik you can expect to lose around 10% in the conversion either away, and diesel engines are rather efficient at various power outputs (unlike turbines, which can benefit greatly from being used as a generator since they can run at their optimal speed... this also eliminates the need for complex gearing).

I do get some advantages of diesel-electric propulsion (rather than having diesel engines drive the propeller directly)... you don't need a direct connection between noisy engines and the outside, you can service your diesel and continue running etc.
But I don't really get how you could save fuel this way in a submarine that's built to have diesel engines for direct propulsion. Were the diesels of the time efficient over a narrower range than later ones or am I missing something? I'd be grateful if someone who knows the history and/or engineering behind this could enlighten me.