four blade props versus three blade props

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Will-C

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C Dory Year
2008
C Dory Model
23 Venture
Hull Identification Number
CD023007A808
Vessel Name
Will-C
Hi,
I have a three blade stainless prop, 14 1/4 x 17 along with a Permatrim which seems well suited for the motor (Yamaha 150hp) boat tops out at 5700 rpms and 42mph. It planes pretty quick now. I'm not concerned about top end. I am headed up north to a less sandy more rocky cruising area (Maine). I want to switch my prop out to aluminum and wondered if I used a four blade should I keep the diameter and pitch the same? I like the idea of faster planing and better mid range fuel mileage if you can believe the promotional advertising. Also when switching from stainless to aluminum with a standard three blade does everything usually stay the same with diameter and pitch?
D.D.
 
I switched from 3 blade to 4 blade aluminum props on our two Honda 40's with results as follows: same cruising speed at 200-300 fewer RPM, lower top end speed by about 5-6Kts, little noticeable difference in time to plane. The 4 blade props are smaller diameter and, as I recall, the pitch is the same. I am still not certain I prefer this setup.
 
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