prop size

patrat

Cadet
Joined
Jul 10, 2008
Messages
15
im looking for some help i order a 4 blade prop 9 1/4-10 for my 15hp 4 stroke motor 4500-5500 rpm thats is the same size prop that came with the motor.but yesterday i got a phone call saying it is on back order and it wouldnt be in until late march so i went with a 9 1/4-11 three blade.well that be alright for my motor.:confused:
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: prop size

We don't know. We need to know the "actual" wide open throttle rpm for your motor with an average load. If it's not in the range you indicated (which is the manufacturers "recommended" rpm band) then no -- it is not correct. Your response will be "but I don't have a tach"! In that case we recommend you install a "Tiny Tach" to determine actual WOT rpm. Then and only then should you be changing pitch. Adding pitch to an engine that may already be "lugging" will increase fuel consumption and eventually kill it.
 

patrat

Cadet
Joined
Jul 10, 2008
Messages
15
Re: prop size

ok i got the wot rpms so 5500 full load.so well the 91/4-11 3 blade prop be allright for my 15hp four stroke honda.
 

junior1113

Senior Chief Petty Officer
Joined
Jan 29, 2009
Messages
763
Re: prop size

what is current prop size and current wot rpm. depends on what the motor is pushing to be able to know if prop will work. imho i would go for the 4 blade they are awsome . all i run
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: prop size

Pat, what manufacturer and year is your motor.


H
 

patrat

Cadet
Joined
Jul 10, 2008
Messages
15
Re: prop size

my motor is a 15hp four stroke 2008 honda bf with a 9 1/4-10 4 blade prop on a 14 ft mirrocraft boat.it gets up and goes at 26 mph but i was wondering if i went with the 9 1/4-11 3 blade prop if i would get a better holeshot and more top end speed.ty pat:) 5500 wot rpms with my wife and i and my gear thats with the 4 blade right now.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: prop size

Pat, I don't understand how you an be going 26 with a 10" pitch prop as that shows a negative 4% PROP SLIP and that is not possible. I assume you are using a speedometer and not a GPS. I show your motor has a 2.08:1 gear ratio and max recommended RPM is 4,500 to 5,500 RPM, if that is wrong let me know as my numbers will be wrong as well. If i had a true speed I could tell you what your prop slip is now and make a recommendation. A phone with GPS or even a handheld GPS would work. I can tell you, you would definitely lose some hole shot.


H
 

patrat

Cadet
Joined
Jul 10, 2008
Messages
15
Re: prop size

i have a speed sensor on my boat that is hooked to my hummingbird 565fishfinder and thats what it reads at full throttle 26mph and i also have a small tack that reads 5500 at full throttle.
 

hwsiii

Commander
Joined
Jan 25, 2009
Messages
2,639
Re: prop size

Pat, you should lose about 300 to 350RPM between the change of pitch and going to a 3 blade.


H
 

patrat

Cadet
Joined
Jul 10, 2008
Messages
15
Re: prop size

so i should stick with the 4 blade.thats probably all im going to get out of my motor right.thank you.
 
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