This topic has been discussed extensively in the 393 newsgroup. Autoprop, maxprop, Kiwi prop and Gori. There are 92 messages dealing with this subject. You might find your answer there. Below is an example:
> I wouldn't get to concerned about it.
> 1. My autoprop propeller
has (only when motoring) a large
> over the MaxProp. The self pitching feature on the autoprop brings
> large boost of efficient, I recall
claims of 20%. While that does
> not translate into a full 20% faster at the same RPM
> at the highest boat speeds, I would expect I would require fewer
> to achieve the same boat speed. Looking at your numbers my boat is
> 16% faster at the same RPM, which is certainly in the ballpark.
> 2. There are lots of other variables between our boats. Even for
> myself, I get different results now. For some reason my boat is
> even faster at the lower RPM's than it was originally (I have a
> problem where I cannot get the speed down to 5, looking into
> throttle control adjustments ), yet my top speed has been reduced.
> (no surprise my top speed is lower, after bringing over 800 pounds
> of stuff onto the boat since I bought her)
beneteau393 : Beneteau393 Group