Quote:
Originally Posted by CaptBones
As I'm sure you realize, the correlation between propeller RPM and propeller HP (and therefore ship speed) is not a straight-line relation; 282rpm/21kts is not equal to 67rpm/4.99kts.
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Not just for propellers. I was just reading a similar set of equations concerning race cars. One of the big problems is drag. Hydrodynamic drag increases as the cube of the velocity, meaning that it takes 9,261 times as much power to maintain 21 knots as it does to maintain 1 knot. it only takes 1,331 times as much power to maintain 11 knots. That gives almost 7 times as much power needed to maintain full speed as it takes to maintain half speed.
This is true no matter what type of propulsion is being used.