Prop size for 1987 GW Overnighter I/O

[Burglar]

I need a new prop for my 1987 GW overnighter 20. It has a 190HP Mercruiser I/O. The current prop seems to cavitate and cannot get the boat on plane with more than two people in it. Any recommendations on prop size? 3 or 4 blades?

 

[JeffN]

What size prop are you running now? Is that a Mercruiser 488, if so the rev range should be on the valve cover. At WOT what do you rev to?

 

[Burglar]

I am not sure of the current size, as my boat is presently in winter storage. The outdrive is a Mercruiser alpha one 190. The manual specs list RPM at WOT of 4400-4800.

 

[JeffN]

Do you know what your RPMs are presently when you run WOT. There should be a stock number on your prop if you can read it that should tell you your pitch. I think you need both of those pieces of info before you proceed but I may be wrong. IMO you probably should wait till next season because you need run the boat to find the RPM so you will then know if you are over or under propped. I had the 470s but in a twin installation with a larger boat and ran 21s but that doesn't help you.

 

[JeffN]

Burglar - Check the "what prop should I buy post" The mercruiser prop selection site would be a good plce to start.