1980 johnson 50 hp

[Quick3201]

Purchased a used 14' fiberglass runabout, almost flat bottomed. Has a 1980 Johnson 50 hp. Needed to replace the prop due to damage. New prop, only one I could find listed for that motor. At WOT, speed is good but only gets to 4200 rpm, should be 5500. Any suggestions on where to find a variety of props?

 

[Quick3201]

Went back to prop guide, everything listed is 13 pitch. That is what I have.

 

[ondarvr]

I just looked here on iboats and there were many options on pitch.

 

[steelespike]

Prop numbers are written diameter X pitch. Generally as pitch goes up diameter goes down. What is the diameter and pitch of your prop.
Get a lightly loaded wot rpm and gps speed.The only way to evaluate your setup.

 

[Quick3201]

Speed was with GPS and light load, 4200 rpm. Every prop I saw was 13 pitch, I'vr been known to miss something. Can you fellows point me to where to look?

 

[Quick3201]

I just looked here on iboats and there were many options on pitch.

Can you tell me exactly where to look?

 

[steelespike]

I don't see where you gave us the wot speed.
I just looked up Johnson props 1975-2005 many props 8" to 19"
Prop size is listed diameter X pitch. Usually as pitch goes up diameter goes down.
The diameter of some props with the same pitch may not be the same as yours. If intended for your motor it will work.
Numbers are usually under the prop nut.
All the way at the top of the prop forum you will find a tab" boat parts and accessories"
put your cursor over the title until the drop down list appears, click on propellors.

 

[Quick3201]

Thanks,

 

[steelespike]

Without your speed we can't help evaluate your setup.
Tachs often are in error. We need your prop size and gps speed.
Without your prop size there is no way to select a prop to solve your problem.

 

[dazk14]

You'll burn that motor out quickly running a setup that tops out at 4200rpm. Tach can be off or you could be running a 13x19 prop, which is way too big.
Listen to the above comments.
Normally aprox 13"x15"P is what works well, BUT....

 

[Watermann]

On my 55 Hp Johnson I run a Turning point 3 blade AL 12.5d x 13p that's cupped, the 15p was too much prop. Your 50 should be darn close to that. So do you have power trim?

 

[Texasmark]

Without your speed we can't help evaluate your setup.
Tachs often are in error. We need your prop size and gps speed.
Without your prop size there is no way to select a prop to solve your problem.

Spike,

Do you have access to his gear ratio? I usually use old-omc.de.com but the site is down.

Thanks,
Mark

 

[Quick3201]

On my 55 Hp Johnson I run a Turning point 3 blade AL 12.5d x 13p that's cupped, the 15p was too much prop. Your 50 should be darn close to that. So do you have power trim?

No power trim. My prop is 12.5 dia. and 13 pitch didn't have GPS with me at that run. Waiting on warmer weather to try again. Thanks for all the help. Will run another test and advise of the results.

 

[steelespike]

Spike,

Do you have access to his gear ratio? I usually use old-omc.de.com but the site is down.

Thanks,
Mark

Hi Mark, My indication is he has a 2.42 gear ratio 1975 -2005.
I used the old OMC site as well,I'm a little lost without it.
It had gear ratios,prop sizes, wot speeds,weights,initial appearance of various models
etc,etc.
www.johnshotprop.com has some pretty extensive rpm a ratio charts.
By the way; E/J 9.9,15,40 and 50 are listed with a 2.42 ratio for quick reference off the top of your head.

 

[Quick3201]

Thanks for the suggestions. I'll try again when I feel better. Clear sky s and favorable winds to you.