Don.
The engine telegraph is an old fashion way of controlling the engine output and the wording of the orders transmitted bears evidence of that. The old marine language both in English and German did not distinguish between diesel, electric motor and steam engine, hence maschine or engine was used for the main engines in both languages generally. In the submarine language we did make a difference between diesel and e-motor. The output and rpm (often called wrongly speed) relation of a dieselengine is following a graph put up at the testbed where the engine is connected to a waterbrake which follows the propellerlaw. The engineroom crew following the engine telegraph orders follows approximatly such a graph by adjusting the HP fuelpumps injection volume in relation to the rpm. Today this is done automatically by the governor.
Beide Maschine 10 weniger, I guess this means the propellers, regardless the powers source.
There could be situations that you would need as much power ( bollard pull) astern as possible when submerged, like sitting on the seabed and getting stuck in the clay, getting entangled in some object like u-boat net etc. In the days before schnorchel you would of course use the E-motors. On the surface likewise due to grounding, ice etc. you would need bollard pull rather than speed, anyhow the dieselengines have to give max.output or the max bollard pull, not speed.
Tore
