Prop angle / Motor HP/ Speed Info

[The Bullhead Guide]

I have a Yamaha 80 HP Boat Motor with a 17 prop
I can get up to 35-36 mph and the RPM is about 3,600

What would happen if I put a 19 prop on?
Would I get my RPM up to 5,000 - 6,000?

What about getting up on plane?

[Hot Runr Guy]

Going up in pitch (from 17" to 19") will reduce your rpms, not increase them. Also, increasing pitch will worsen your holeshot, or take longer to plane. But,,,, I'm a little suspect of your rpm #'s, since a 17" at 35mph would tend to be at a higher rpm than 3,600. Which Yamaha 80-hp do you have (year, 2S or 4S)? Is the speed checked by GPS, or the dash speedo? What hull is this on?
Thanks, HRG

[The Bullhead Guide]

The boat is an Alumacraft 2001 Mag 165CS
The motor is an F-80 Yamaha
I checked the speed with two (2) seperate GPS's

[Hot Runr Guy]

digging back thru the archives, here was a posting on a similar (but newer) 165 CS w/a F75 on it:
Nimstug10-05-2008, 05:14 PM
Boat: 2007 Alumacraft 165 CS
Motor: Yamaha 75 H.P. Fuel Injected 4 Stroke
Gearcase: I suppose there is one
Jackplate: No
Prop: 13 1/2X17 stock aluminum
Top GPS Speed: 37.7 mph no wind, dead flat water
Average GPS Speed: 20-23 mph
Load: 2 People 1 battery, 15 lb anchor, 8 rods, small cooler,
Air Temperature: 40-95
Water Temperature: 40-80's
Elevation: 650
RPMs: 5700 at WOT with stock prop

I think your tach may be set wrong.
HRG

[1625rebel]

Agree on your tach being off. There's no way you can get to 35 mph at 3600 rpm. The top speed sounds about right though.

It takes all 6000 rpms on my 16' Lund to get to 39-40 mph with my 75 Yamaha, this with a 13.25x17 aluminum prop. At plane, which is around 3400 rpm's, I'm only in the high teens to low 20's for speed.

Until you get a reliable tachometer reading, I wouldn't try changing props. You don't want to over-rev your beautiful Yammie. Good luck!