Prop Question. I'm stumped!

[eward4]

So, I have a 150 hp Optimax that I decided to replace the aluminum prop that came on it with a stainless. I found a Mercury Mirage 17 pitch with a 15.5" diameter which was too big for that motor. I used it for a while but it would only turn up to 5100 RPMs at WOT. The range for that motor is 5250-5750. I finally decided get a smaller diameter prop since that Mirage would also stall the motor sometimes when shifting from reverse to forward. It was just a lot of prop to stop and start in another direction. I got a 17 pitch 14.25" diameter Michigan Wheel Apollo prop since I was told 1" in diameter reduction would add about 400 to 500 RPMs to my WOT. Well, it actually took 200 RPMs off! So I went from 5100 with the 15.5 diameter to 4900 with the 14.25" diameter! Am I missing something here?! The boat is a 23' C-Hawk with a 14 degree transom dead rise and weighs about 3000 lbs full of fuel. Mercury recommends a 14.5" Diameter 17 pitch prop for that length and weight. Could it possibly be a throttle cable adjustment? I have it pinned as far as it will go. The motor seems to be running fine just like it always has. I'm stumped!

[rchavis]

There a lot of if's as ,what boat and set up . If on a bass boat and set around 3. 50 below pad you should be able to turn to 5600 or 5800 rpm.
A Tempest plus 23 p would be a good choice .

[EuropeanAM]

If you would, please take a moment to review the Announcements at the top of the Forum, and be sure to provide the Required Info with each post. Thanks!

Pay attention to the particular propeller MODEL and PITCH (and less attention to DIAMETER). Diameters vary among a particular prop line- and are adjusted, along with PITCH, to achieve a specific RPM and performance difference.

Mirage is traditionally a BIG blade prop, designed for LARGE, HIGH-HORSEPOWER boats.

[SilverFox579]

I checked to see what a C-Hawk is and the OP has 23' center console bay style boat. JMHO, with a deep V, non bass boat, rigged at 67% of rated hp (max 225 per manufacturer's website) you need to drop diameter and pitch. General rule of thumb is 200rpm per inch of pitch or diameter and which is what your 1" change in diameter produced. You may need to drop an additional 2" in pitch and get something in the 14.5 dia X 15 pitch range. I think contacting boat C-Hawk for their recommendations with your setup might be helpful.