just put a different engine on my boat...which prop

[8bwild]

I am new to the prop game...here's what I have 1994 suncruiser pontoon that I just put a 120 hp Johnson on and I have a 13 1/4 x 17 aluminum prop and a 12 3/4 x21 steel prop which one should I use??

 

[steelespike]

Re: just put a different engine on my boat...which prop

Welcome,
We need more information.If you answer the information requested in the stickys at the top of the prop forum as best as you can we can help.
Prop selection especially on a pontoon can be difficult.
Depending on the information you get us both props are wrong. It might be possible to do a test run with the 17
and a very light load to get us some base numbers.You will probably end up with a 13" pitch as a starting point.
If you read the helps on the prop store page and the stickys mentioned it may give you a basic understanding of props.
We'll be glad to help with prop selection and any confusion.

 

[8bwild]

Re: just put a different engine on my boat...which prop

Well I just put the engine on and haven't had it in the water yet so I don't know the rpm's....it's a 1994 20 foot suncruiser the engine is a1992 Johnson 120 the props are what the guy gave me when I bought the engine from him

 

[The Rooster]

Re: just put a different engine on my boat...which prop

That 120 Johnson should be rated for 5500 rpm's max. You need to prop for that, and let the speed fall where it does. Forget the 21". Try the 17" but you'll probably wind up w/ a 13 to 15". Good luck !!!

 

[8bwild]

Re: just put a different engine on my boat...which prop

Thanks a lot I just wondered which was best to start out with ill let ya know how it goes.....thanks again