Yamaha prop

I have a 2005 yamaha 15hp 4 stroke and my current prop is 91/4 x 11 I am wanting to reprop to get higher rpms. What size prop should I get? Thanks in advanced

How many more RPMs are you looking for? Typically every inch in pitch you go down increases rpm about 200 but I wouldn't recommend doing this unless you have a good RPM reading on the current prop and know you wont be going over engine RPM specs by going down in pitch. But going to a 10 pitch should give you roughly 200 rpm increase...... 9 pitch 400....... 8 pitch 600......etc

not sure exactly what rpm im running or what i want to go to, my motor just sounds like its not running what it should. is there some way that i can test rpm's with out having to install a tach?

T-MAN said:

not sure exactly what rpm im running or what i want to go to, my motor just sounds like its not running what it should. is there some way that i can test rpm's with out having to install a tach?

Click to expand...

How fast can you count?


You are going to need a tach - they are really cheap

https://www.amainhobbies.com/product_info.php/cPath/89_2049_609_610/products_id/23619/n/Hanger-9-Micro-Digital-Tachometer?utm_source=Google-Base&utm_medium=cpc&utm_campaign=Product-Feeds&source=google_ext&gclid=CPfogNjwyrUCFYdT4Aod43gAYw

^^^^ agreed, without an RPM reading you are shooting in the dark and jeopardizing damaging your engine. Tiny tachs are about $50 and easy to hook up.

ok thanks guys! looks like a tach is in the near future. then ill post back when i figure out the reading

Where do you find the RPM the motor should be running at?

Where do you find the RPM the motor should be running at?

https://www.yamahaoutboards.com/outboards/Portable/specifications

Prop Shaft Horsepower 15hp @ 5500rpm

Ringo Steele said:

https://www.yamahaoutboards.com/outboards/Portable/specifications

Prop Shaft Horsepower 15hp @ 5500rpm

Click to expand...

Does this mean I am already running this many rpm's?

No, the only way to tell for certain what rpm you are running is a tach. It is just engine specs...... What it says is your engines optimal rpm operating range is between 5000 and 6000rpm with 5500 being peak performance of horsepower. Go above or bellow 5500 and engine produces a little less horsepower.

Johny25 said:

No, the only way to tell for certain what rpm you are running is a tach. It is just engine specs...... What it says is your engines optimal rpm operating range is between 5000 and 6000rpm with 5500 being peak performance of horsepower. Go above or bellow 5500 and engine produces a little less horsepower.

Click to expand...

Ok thanks! That makes sense