What prop size for 1976 55hp Johnson and how to measure?

[mallardtone-man]

I have a 1976 55hp Johnson I just bought for a duck boat and will be needing a new prop on it. I need to know what size I am looking for as well as how to measure it. I am not really concerned about speed, more power as the boat is relatively heavy and will be loaded down with guys and gear most times. I do not understand anything about pitch or what makes the difference in speed and power. Can someone please steer me in the right direction?

 

[Bondo]

Re: What prop size for 1976 55hp Johnson and how to measure?

I need to know what size I am looking for as well as how to measure it.

Ayuh,....

No need to Measure,....

Just pull the prop off,+ read the #s....

 

[steelespike]

Re: What prop size for 1976 55hp Johnson and how to measure?

You need to run the setup with the present prop and get us the figures.
Max rpm and speed,Boat type/weight and typical load.
Should be numbers on the prop usually on the barrel but somettimes under the prop nut. _ _ X _ _ or a part number. Pitch is measured in inches
12" pitch; theoretically the boat will move 12 inches for each revolution of the prop (disregarding slip). Increasing pitch(Higher number) lowers rpm,increases speed assuming the motor can twist the prop.Decreasing pitch
increases rpm increases power lowers speed. there are exceptions.The motor needs to operate within its rpm range I believe the max for yours is 5,500 They generally shoot for the high end of the rpm.
If you need a tach a tiny tach is reasonably priced and easy to install
and will work on any similar type motor without regard to stator poles.
gps speed is best.