3 Blade to 4 Blade change question

tim.m.lounsbury

Recruit
Joined
Apr 4, 2013
Messages
1
Hello,

We currently have 3 blade aluminum 18" 23P on Bravo 2 drives 5.7L mercruiser. We are looking at getting 4 blade stainless steel 18-1/2 22P.

What differences might we expect in terms of RPM and whole shot?

Thanks!!!!

Tim
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
15,417
The hull, motor, prop size and design all factor in to how well a prop performs on a given boat.

Unless your changing from one size to the next of the same brand and make of prop, all bets are off on how the change will react on any given boat.

I went from a Evinrude 4 blade Stainless to a Mercury 3 blade stainless. Better hole shot. Higher top end and a better all performing prop.

Your results may vary..
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
17,625
You might want to go to a 21 P 18” Dia to maintain your top RPM.

Going down 1 in pitch while going up in diameter may not work out.
 

rothfm

Ensign
Joined
Sep 26, 2006
Messages
913
Not a prop guy really, can only state experience. Disclaimer: Like stated, so many factors can affect the outcome.

My boat was a 20-21 walk-around outboard. Fairly heavy with gear. I felt I had to run alot of RPM to remain on plane. I went from 3 blade Alum to a 4 blade stainless. Went down 1/2" in Diameter, and down 2 pitches. Only slight WOT RPM drop. But now I can remain on plane at much lower RPM, still good hole-shot, and no noticable top end difference. Really love it on my rig. Cant say enought about the difference.
 

wrench 3

Commander
Joined
Aug 12, 2012
Messages
2,108
My prop guy always says to drop a pitch when going to a four blade from a three. This is assuming that top end RPM is OK to start with.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
I’d say you’d see better hole shot, similar rpm but a fairly substantial drop in top end speed and fuel economy
 
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