Which prop for a Johnson 15 hp 2 stroke?

[Stud man]

Finally got my 15 hp Johnson 2 stroke. Just wondering what size prop to get? It's a 2005 and the guy I bought it from says all depends on how I am using the motor. ​

Ok so.... I am putting it on a Zodiac 310 rib , about 11' long and weights 106 lbs. Most of the time it's just me and the wife, about 375 lbs and a small amount gear, safety stuff, fuel (6gal) and cooler (15lbs) so I am thinking total weight ( boat, motor, fuel people and gear) about 625 lbs. Thoughts? What prop are you running? Thanks​

 

[Sea Rider]

Which is the current diameter/pitch of the prop that's installed on the motor if having one ? check prop body to find that out. You need to tach motor with an induction tach on calm water as loaded during a wot spin.

Need to know what's the max wot rpm achieved during the test, from there can go maximizing other prop pitches to suit your boating requirements and load.

Happy Boating

 

[Stud man]

unfortunately the prop on the motor is trash and it was setup for a completely different size and weight boat.
So I am starting from scratch

 

[Sea Rider]

Check if number stamped is still visible on prop body. Those Johnies didn't have too many props to choose from. Used to have same engine and the only OEM props available at that time and seems still now are :

9.5 X 10 for 9.9 use.
9 X 11 for 15 HP *
10 ​​​​​X 7 for sailboat use

Ideal is to have a starter prop to check if performed right for your current application and load, if not can go for a prop maximization to a lower pitch prop to pull wot revs upwards if in need. But without an induction tach installed won't know if engine revs at least middle to max wot rpm range, when playing with props wild pitch guesses or ear taching doesn't work, could ruin your engine in the very short term.

Happy Boating