Considering they say there is a 50% drop in fuel use,...... well that would indicate to me that the engine is applying far less horsepower at the same prop speed which on the surface seems hard to swallow
Efficiency is coming from the prop just like one can fine tune/resize/change materials on an application for better efficiency resulting in better fuel economy. The Sharrow design implies it is twice as efficient at moving the test boat at certain speeds which I do agree is either hard to swallow or an amazing feat of engineering.
Done by boat test, I do tend to believe their numbers. With all the thousands of smaller Bayliners out there, someone would shout out the BS after paying 5 grand for a prop if it did not deliver close to what boat test claimed. The big question is, can they be repaired/balanced or does one need to cough up another 5 grand after a bad hit? Maybe paying twice the fuel cost may come out cheaper in the end.