Hm, one more thing...
I've noticed that you was exploring extensively dependencies between max engine turation(aka RPM) and submarine speeds, right?
Didn't you realize that max engine turation value has nothing to do with submarine performance? Even if you set some lower value , like 100 for example, the sub will still have the same max speed and acceleration performance. What will be reduced is submarine noise signature(as far as AI is considered), animation of propellers rotation and values shown in RPM gauges...
In short, with full speed ahead, you'll have sub which speeding up to ~17.9 knots but with much slower propellers rotation and rpm gauge will show you 100 rpm...