New prop for '86 Classic 50 45hp Merc

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ksbass

Cadet
Joined
Aug 25, 2010
Messages
7
I bought an '86 V-17 Bass Tracker with the 45HP merc (sn OA996289) last summer. I've worked through several issues but she's running nice now. Previous owner had put a new Michigan Wheels Apollo SS 10 1/8" x 15" pitch prop on it a few months before I bought it. He told me the old prop was dinged badly and wanted more speed. Anyway she runs right at 4850 RPM at WOT (28mph gps) with just me in the boat. Merc manual says 5000-5500 on this engine. I would like to re-prop and like the apollo prop so thought I would bump it down a few inches and pick up the RPM. I need a sanity check here before I order a new one. Should I go from the 15" pitch to a 12" or 13"?
Thanks!
Troy
 
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steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: New prop for '86 Classic 50 45hp Merc

I'm going to assume it has a gear ratio similar to the 50 about 1.70 and not the 40. 2.0 I think the 15" is too much. It would appear that you need a pitch reduction.A 3" decrease could get you about 600 rpm maybe more. MY old 65 Merc 500 is running an 11" pitch on a 375 pound 57 18ft Crestliner utility .
 
K

ksbass

Cadet
Joined
Aug 25, 2010
Messages
7
Re: New prop for '86 Classic 50 45hp Merc

Thanks Spike,
I just confirmed with the magic marker and hand turn the flywheel technique that the gear ratio is 2:1. Yes, I'd like to pick up about 600 RPM and put her close to 5500 at WOT. I believe I've removed all other possibilities for the low RPM at WOT and it's just the 15"p prop is too aggressive. Do you think a 12" pitch would put me there?
Thanks.
Troy
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: New prop for '86 Classic 50 45hp Merc

Rule of thumb is "about" 150 to 200 rpm per inch.That is assuming same brand same model prop.
The 12 will surely improve hole shot,stay on plane easier. If I'm doing the math right very basic calculations disregarding slip 5,500 rpm you might make 29 or 30.
 
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