[swdw]

Originally Posted by TorpX

The difference between 20 and 19.5, or between 21.5 and 20.75 may seem trivial, but it takes 8 times the power to obtain 2 times the speed, so the difference is greater than it appears at first glance.

Actually, this is how it should be. Even though the boats were diesel electric, the load on the generator will affect the RPM. On a VERY basic level it's effect is similar to friction. Increased load makes the engines work harder to maintain RPMs. There's a point where the load is great enough, the RPM's drop off slightly. The harder you are charging, the more load you are generating, so the engines have to work harder to run the generators. This will drop your speed. Think of top speed difference in a car going flat and level and driving uphill. You can't reach the same top RPM going uphill, and it takes more fuel to hit the max RPM you can achieve under the increased load. Surprised that, with all the other physics left out of the sim, this effect is seen at all.