4 Blades prop on Johnson 9.9 hp - what to except ?

pecheux

Lieutenant Junior Grade
Joined
Jun 9, 2006
Messages
1,200
Good day y'awl, (lol)

Hit bottom rocks and original prop got dinted so thinking of keeping it as a spare and getting a new one, maybe a 4 blade 9 pitch

Considering the original is a 9 X 10 3 blades what would I expect for results with a 9 X 9 4 blades (one inch less pitch) ?

Thank you.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: 4 Blades prop on Johnson 9.9 hp - what to except ?

Typically it is suggested to drop an inch of pitch for a 4 blade,so thats good.
Your results would depend on your performance with the old 3 blade.10"
What boat and typical load expected.
You should have a tach and gps to do it right for best performance and the health of your motor.
Assuming motor was setup right your rpm should remain about the same Hole shot and mid range performance should be better
Should stay on plane easier at reduced throttle. Probably lose a little top end.
 

pecheux

Lieutenant Junior Grade
Joined
Jun 9, 2006
Messages
1,200
Re: 4 Blades prop on Johnson 9.9 hp - what to except ?

Steelspike: The boat is a 14 footer fiberglass. Performance with 2 onboard and 9 x 10 prop = Labors on hole shot to get on plane (barely) but once there I can throttle back a little (a hint). But it will get off-plane if I face some winds gusts. I would be looking for a way to get just a hint more push power to correct that. By your feedback I would guess I would get just that with a 4 blade prop huh ??

It did cross my mind to acquire a 9 pitch 3 blade for more power but it would make the OB over rev when I would be alone in the boat. At this time with the 3 blade 10" pitch prop and alone in the boat it will go as fast as any 15 hp OB and over revs so I have to throttle back some. Obviously tempted by the 4 blade 9" prop Tx
 
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