Prop Selection ? 22 X 14.5 four blade

[ppmeis]

36 foot, aft cabin, single Lehman 120. What size prop are other owners running ? I have a damaged 22 X 14.5 four blade (ran it all last year) also have a 22 X 15 three blade as backup. What are you other guys running ? Before i damaged the 4 blade I was running about 1750 RPM at around 8 - 9 knotts, nice and smooth, seemed like good economy but wondering if anyone has better ideas. thanks, pete.

[jleonard]

What tranny ratio do you have?
What is your WOT rpm? Is this with a calibrated tachometer?

I have a 40 with a Lehman 120. 1:91 to 1 tranny ratio. 20 x 16 4 blade prop. On a good day I can get about 8.3 knots at 2500 rpm (WOT) with a calibrated tach.

EDIT: At 1750 rpm I am doing about 6.5 /7 knots

[psneeld]

36 foot, aft cabin, single Lehman 120. What size prop are other owners running ? I have a damaged 22 X 14.5 four blade (ran it all last year) also have a 22 X 15 three blade as backup. What are you other guys running ? Before i damaged the 4 blade I was running about 1750 RPM at around 8 - 9 knotts, nice and smooth, seemed like good economy but wondering if anyone has better ideas. thanks, pete.

While no expert..something doesn't sound right. Your 120 is rated for 2500 RPM and at 1750 RPM I'm reading you are putting out around 80hp. I have a hard time believing you get 8-9 out of 1750 RPM when my and other 40's are only getting 6.5 maybe 7 knots. If you are...then back it off even more as your hull speed is way less than 9 knots and your economy will be better.

What was your max RPM at full throttle?..should have been close to 2500.