Help with a 1966 johnson 40Hp electric shift

[AmberBock]

I am trying to find the right prop for this 1966 Johnson 40hp sea horse electric shift. The engine will be on a 13 ft Boston Whaler sport. The width of the boat is 5 ft. Does any one have a good idea for the right size prop I need on it? Pitch, size? Thanks

 

[steelespike]

In 66 it came with a 12" pitch prop. Three others optional, 11 1/2, 13 1/4, 14".
The size of the present prop should be near the base of the blades or possibly on the hub.
A test run with the rpm and gps speed and present prop size would help.
Gear ratio is 1.75. Only 2 sizes available here at iboats. 12 and 11 1/2.
I think a 12" is a reasonable starting point. Do you know the dry weight of the boat?

 

[AmberBock]

Thanks for your reply. I think the dry weight of the boat is 300 lbs.

 

[steelespike]

Pretty light so at least a 12" Check what is on there now.
​ If we can get the prop size, wot rpm and gps speed we can tell if your setup works and if you need to replace the prop.
If your going to be trying to find the best prop you will need a tach and a gps for speed.
An induction tach should work well.

 

[AmberBock]

Thank you