Need input on switching from 3 to 4 blade prop for slightly better top end please.

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NL2

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Joined
Mar 10, 2012
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2
Hey everyone,
Im new on here so please excuse if this answer or similar post is right in front of my face and I missed it. Ive tried searching but to no avail.

I have a stock OMC cobra 195 sundowner, 1995. I am really hoping to upgrade the oem prop for a better cruising speed/ help increase gas mileage. I doubt i could increase hole shot and top end, as sacrificing one would increase the other; correct? I have the smart tab trim tabs and the wing on the outdrive above the propeller (unfamiliar with the name). Any help would be greatly appreciated. Thank You.
 
chriscraft254

chriscraft254

Commander
Joined
Jun 4, 2011
Messages
2,445
Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

This is an I/O correct. If so, loose the hydrofoil or "wing" as you put it. If there is one on the outdrive. they will not help your performance and may be causing drag and other issues. You have smart tabs, you don't need the hydrofoil on there. I would start there.
 
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Lyle29464

Lieutenant
Joined
Mar 10, 2009
Messages
1,261
Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

Most changes to 4 blades give a little better hole shot a little better stern lift about the same cruise and a hair less top end.

If your running the correct RPM at WOT now I don't see how you could ever recoup the price of the 4 blade in mileage.
 
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steelespike

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Joined
Apr 26, 2002
Messages
19,069
Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

Welcome,
If you have a whale tale or doelfin etc and Smartabs you may have a serious performance issue.Lets hope someone was just lazy and didn't remove the "fin/foil" when they added the smart tabs.Both devices improperly installed and used can actually reduce mileage.
Read "read this first" at the top of the page,remove the "Foil"and do some testing and get us as much info as possible.
Describe hole shot and general performance.We'll get you setup.
 
F

fishrdan

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Jan 25, 2008
Messages
6,989
Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

I agree, loose the hydrofoil, do some testing with the current setup and report back with your findings.

NL2 said:
I doubt i could increase hole shot and top end, as sacrificing one would increase the other; correct?
Click to expand...

If you have a poorly matched prop, you could improve both holeshot and top end speed. I did this when I went from a 15.5x19P 3 blade to a 14.5x18P 4 blade. The hole shot was MUCH better and I picked up around 2 MPH top end. Off the boat's speedo, it went from 32-33mph at 42-4300rpm to 34-35mph at 45-4600rpm.
 
N

NL2

Recruit
Joined
Mar 10, 2012
Messages
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Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

Hey, thanks for the help. You are correct, I had the hydrofoil on it and just received the smart tabs last week. That's good to know that I should remove the hydrofoil with the trim tabs. I'll let you's know how they works out. I bought them mainly for planing out.
 
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steelespike

Supreme Mariner
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Apr 26, 2002
Messages
19,069
Re: Need input on switching from 3 to 4 blade prop for slightly better top end please

All tabs whether active or passive need to be set carefully to achieve best results.Regardless it is very likely a flow meter would be necessary to measure the difference in mileage.
A test I saw power tabs delivered the best mileage fully retracted.
Of course tabs can improve ride and handling but heavily applied reduce mileage.
Again telling the difference in mileage would be difficult.
 
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