Prop size and pitch for 1968 120hp mercruiser I/O

[wrfalpacas]

What was the original prop size / best choice for my 1968 starcraft starcheif aluminum cuddy cabin? It has a 120 hp mercruiser I/O 2.5L GM engine.

Thanks for your help!

 

[robjen1019]

Re: Prop size and pitch for 1968 120hp mercruiser I/O

Ive got a 1968 larson that looks alot the same. I use a 15x13 pitch for pulling skiers and tubs, and a 15x15 pitch for cruising. I tried a 17 pitch, and the rpms just werent high enough.

 

[cr2k]

Re: Prop size and pitch for 1968 120hp mercruiser I/O

Since most boats are proped by the dealer NOT the MFG. The original may or may not be the correct prop for you application. If the boat came from high altitude it would have a lower pitch prop.

Your boat should be proped to achieve max engine (recomended) RPS at your most used loading configuration. 2" lower for pulling is OK. But watch RPMs when unloaded.

 

[GunHoInc]

Re: Prop size and pitch for 1968 120hp mercruiser I/O

That explains alot for me. I have a 14 1/4x19 3 blade and the RPS was perfect. But I saw a chart for my Sea Ray and it said to use a 14 1/2x17. Not sure if that was the dealer or the MFG. I just changed props to a 14.5x18 four blade for pulling my sons tube. Havn't checked the RPS on it yet.

Paulie