What Size Should My Prop Be

[KQQLCAT]

I have installed a tachometer on my 20' pontoon boat becuase I thought that my motor was not reving high enough. I have a 2005 Mercury 60HP 4 stroke bigfoot and now I know it's doing 4,000 rpm's at full throttle at about 19-20mph.
I have a 15 pitch prop on there now. What should I go to.
Thanks

 

[steelespike]

Re: What Size Should My Prop Be

It does appear you need a prop change but you need to make up about 2,000 rpm.
You can't do it all with a prop alone. Rule of thumb is "about" 200 rpm per inch of pitch.
Lower number increases pitch.I do think that something is up with the motor.Maybe as simple as the throttle
not opening all the way.Maybe one cylinder dead.I think see whats up with the motor and you will probably pick up some rpm.
then make the decision on a prop.