Prop diameter question

[matthewp]

I just acquired a 2002 Johnson 115 2 stroke. The dealer I got it from sold it with a 15" 3 blade aluminum prop - 17" pitch. WOT is about 5400. My old 85 Johnson 115 had a 13" diameter 19" pitch stainless prop. All searches for Johnson 115 props return 13" models. What's the danger in running a 15" where a 13" seems to be the recommended diameter? I still have my old stainless prop. Should I be using it instead of what came on the motor?

 

[sschefer]

Re: Prop diameter question

An inch in diameter is about the same as an inch of pitch. a 13 x 19 and 15 x 17 are pretty close to the same.

 

[matthewp]

Re: Prop diameter question

That's good to know. Thanks for the speedy reply!

 

[Dhadley]

Re: Prop diameter question

It'd be nice if it was that simple. Props with different diameters may have more or less bite or efficiency. It all depends on prop design. As for your 2 props working on your current motor it's pretty simple on an Evinrude / Johnson. The 4.25" gearcase uses a 13 spline prop. The 4.75" gearcase uses a 15 spline prop. Your old motor had a 4.25" gearcase and used a 13 spline prop. If your new motor has a 15" diameter prop it probably has a 4.75" gearcase with a 15 spline propshaft.

 

[SparkieBoat]

Re: Prop diameter question

your WOT RPMs are right on where it should be, maybe a couple hundred low, but a good range. if it runs out good for you, then dont change a thing.