Prop size

[AstroDiver]

Having dropped off my lower unit of my Suzuki, I removed the prop. It's a three blade 14 x 20. The Suzuki shop manual has pitch sizes listed as: 17, 19, 21 and 23. The motor is a 2002 DF115.

A few years ago, I was wondering why my boat would not get very much speed? From the size prop that came with the boat, which way would I go to get more speed? I think the fastest I even got the boat was 34 MPH? I was told that I should get better than that. Would an increase in speed mean less mileage? Or more?
I may just stick with what I have seeing that SS props are so expensive.

Thanks for any help.

 

[BarryB]

Generally, at WOT (with the boat devoid of extra gear, people, etc.) , your engine should turn at the high RPM end of the specs posted for your engine. That way, when you load down the boat, you will still hit the lower to middle range of RPM at WOT.

Too large a prop will load down the engine, too small a prop will cause over-reving. Find the sweet spot and don't fret about an extra MPH or two.