Prop question...

[Janniklindskov]

Hello
I have two props for my 90 hp Johnson 1986.

1: 13-1/4 x 17
2: 12-3/4 x 21

What is the difference in the two props? - is one of them for high speed and the other for torque or how is it with props?
Jannik

 

[DJ]

Re: Prop question...

Yes and no.

You need prop your engine based on top RPM attainable. Your engine needs to turn at least 5500 RPM, with a light load. Choose which prop allows you to do that.

Unless your boat is very light, I doubt you can reach 5500 RPM with the 21" prop.

 

[Janniklindskov]

Re: Prop question...

Hello DJ

Thanks for the quick reply. I don't have an RPM gage in the boat, but it is a Labrador 14,3 foot speedboat (a bit like the fletcher model) I realy don't know what my max RPM is but i'm runing the 12-3/4 x 21 prop and the boot is fast out of the water and the top speed is around 75-80 Km/h which is around 46-49 miles.