Originally Posted by Nos4r2
That works, but then you're going to have the most economical crusing speed/RPM with the prop that gives you the highest top speed-unless you can find a prop that slips significantly less at cruising RPM.
Not in my experience of comparing two props on the vipermax.
It originally came with a 21" which was running towards the bottom end of the WOT range.
I bought a 19" off of ebay and tried this. Whilst giving me any more Top speed at WOT is actually gave me less speed at 3000rpm. If memory serves me it was about 3 knotts different. They where back to back trials in the same sea conditions.
No serious difference in acceleration either.
So with 2knotts faster speed at 3000rpm and 250RPM lower WOT I'd have to deduce that I'd be getting more miles per gallon at my usual cruising speeds with the 21"er.