[TEC] Tweaking submarine ranges

[LukeFF]

I'm trying to adjust the submerged engine performance for RFB, but I've run into a bit of a wall here. First off, a quote from the Fleet Type Submarine manual:

Navy type engines are generally rated higher for emergency use than would normally be the case with commercial engines. The economical speed for most Navy type diesel engines is found to be about 90 percent of rated speed. For this speed the optimum load conditions have been found to be from 70 percent to 80 percent of the rated load or output. Thus, we speak of running the engines at an 80-90 combination which will give the engine parts a longer life and will keep the engine itself much cleaner and in better operating condition. The 80-90 means that we are running the engine with 80 percent of rated load at 90 percent of rated speed.

Now, the problem is that SH4 seems to have some sort of optimum engine efficiency built in at around 50 percent of rated speed. I've tried tweaking the range on the Balao, for instance, to be 15000 nautical miles at 18 knots (that 90 percent thing). However, that results in a fuel efficiency of around 41000 miles at 10 knots! Does anyone know how to get around this problem? I've tried, for instance, to put the maximum range at 5000 miles at 5 knots, but this just results in a "maximum range not available" message from my navigator.

Any help with this would be much appreciated. Thanks!