Prop for a Johnson 80HP

[grehmer]

This question relates to prop functionality more than anything, which I can probably read somewhere online but there are specific questions I would like to ask regarding my motor and boat. I have a 1966 Johnson 80 hp motor on a 1966 Glasspar Avalon that I?m just beginning to restore. The original sales literature for this specific model Johnson states that a 3-blade 10 ? in X 10 (I assume diameter X pitch) is standard equipment for the motor. However, optional sizes were offered which included;

9 ?? X 10?
10? x 9 ??
10? x 11?
10? x 12?

My question; what is the significance between the different size props? Does one provide more thrust, or higher speeds, or better fuel economy? If there are differences between each of these prop sizes, which would you recommend I install on my boat?

Thanks for any advice.

 

[usskydvr]

Re: Prop for a Johnson 80HP

The lower pitch (9 1/2) will have more power, the higher pitch (12) will have more speed (assuming the engine has the power to turn it depending on load). In order to determine the best one you will need a tach to be able to find out what the max RPM you can get with a normal load (1/2/3 people + gear) and the current prop. I am not familiar with the Avalon, how long/what kind of boat is it?

 

[Teammuir1]

Re: Prop for a Johnson 80HP

Correct me if I am wrong... but prop size that the manufacture recommends is the base line...
The correct prop for your boat will and can only be answered by you and several tests....
Need to know RPM and SPEED while testing each prop out.
could be very costly if you buy each prop...
but there is an alternative My boat shop will allow you to RENT props to test.
might want to check into that when the time comes.

 

[NapaBavarian]

Re: Prop for a Johnson 80HP

Did you purchase this motor in either the Modesto area or Lincoln CA are without a prop? My stolen boat had a large Johnson on it and the prop was missing.

 

[grehmer]

Re: Prop for a Johnson 80HP

The boat and motor were purchased together from the original owner and there is a prop on the motor right now in need of replacement.

Anyway, thanks for the info everyone. When I get the motor running and boat in the water I will start some testing. This boat is fairly light (16' long) so I'm sure that any of the prop sizes will have enough power to move the boat fully loaded. Maybe in the end it will come down to cost.