Prop ??????

[arall]

Hello All,

My question is this, I have a 1989 Johnson 48 special outboard the prop is 11-3/4" x 17 pitch. I was wondering if I'm able to replace it with a 12"x17 pitch prop. and if not, why not? this would be very help full to me.

Thanks,
Al

 

[cougar1985]

Re: Prop ??????

not a prop guru myself but you could check the michigan wheel site and see what was available for your motor.

 

[Gary H NC]

Re: Prop ??????

If it has clearance and does not hit the cav plate i don't see why not.

 

[cougar1985]

Re: Prop ??????

did a quick peek on michigan wheel and shows you could go to at lest 12 1/4 so i dont see why not for the 12x17 as long as your not going to be over or under reving.

 

[arall]

Re: Prop ??????

Gary:

What is the cav plate is that the plate that holds the zinc trim tab above the prop?

Al

 

[arall]

Re: Prop ??????

cougar:

thanks for that info. that was my concern the rpm's. I'm not sure what the wot rpm's are for this engine for using the best prop. in my search they all point to 11-3/4x17

Al

 

[Silvertip]

Re: Prop ??????

Your engine can run a 12-1/4 diameter prop and there are about a zillion of them that do. 12-1/4 x 15P was a fairly standard prop for that engine on 15 and 16 foot boats. Diameter will not change rpm much. Pitch is what affects rpm the most. If you are running a 11-3/4 x 17P now, a 12 x 17P will very likely not be noticeable. My question to you is why are you changing props if you have no idea what the WOT throttle RPM is for the engine (it's 4500 - 5500 by the way) or what the engine actually turns at that WOT. If you have no idea what the RPMs actually are or what speed you are running you should not be spending money on props. If the engine is not capable of reaching 5500 rpm, you need to decrease pitch. If the engine revs above that range, you need to increase pitch. And before doing that, check the engine mounting height to make sure the AV plate is at least even with or an inch or so above the keel. Then make sure the engine is properly tuned and performing as it should. Now you can spend money on props -- if necessary.

 

[arall]

Re: Prop ??????

Silvertip:

the prop that is on the boat when purchased, is a 11-3/4x17p I only asked about the 12x17p because a buddy of mine has one that's like new and the best of all, it's... FREE. and as for the rpm's thanks for that info. the CAV plate is level with the keel. I'll remove the broken prop and bring it to someone who can run a test for the rpm's at WOT.

THANKS GUY'S FOR ALL THE INPUT.