Prop size and Pitch?

[larryman98]

Hello all, i am wondering, can anyone tell me what size prop and with what pitch i should be running?
I have a 1989 21' Galaxy Magna walk around cuddy. It has a 3.7 165 hp Mercruiser with an Alpha One outdrive. The existing prop is 14 1/2" and 17 pitch. My WOT RPM's range sticker says 4200-4600. At full throttle i am at about 5100.

Thank you.

 

[craze1cars]

Re: Prop size and Pitch?

What is your actual speed at full throttle 5,100? And what is your outdrive's gear ratio?

Generically speaking, you should add about 3 inches of pitch and change to a 20 pitch of a similar design/material to get your RPMS in the upper end of your range. This assumes your tachometer is accurate, and that our current prop is in good physical condition.

Keep in mind that the majority of 20+ year old boat tachs are flat-out wrong.....

With the above two pieces of data, we can probably use a prop slip calculator to tell you if your tach is accurate, and if your prop is working like a 17 should be working...