Another Which prop for me question.

[iwombat]

I'm currently pushing a 18' Starcraft SS with a '77 85hp Johnson. The current prop is 13x19 and turning 5000rpm at full throttle. I'd like to re-prop to get 5600 or better.

Any advice welcome.

 

[Bob_VT]

Re: Another Which prop for me question.

13 x 17 will get the rpms up a bit but you should check your current set up before you invest in a prop. We are talking about a 30 year old outboard so I would not strive for max rpms.

Check your set up..... engine height first. Raising up a single hole (an inch) if you have that amount of room will increase rpms too.

 

[redjmp]

Re: Another Which prop for me question.

Gain or lose 200 rpm for 1" change of pitch. Go from aluminum to steel and gain 100 rpm so in theory a 17 steel if you have alum or 16 steel if you are running steel.

 

[iwombat]

Re: Another Which prop for me question.

Thanks for the info.

Cav plate is even with bottom of the transom and the engine is in excellent shape - even for a 30-year old.

 

[Bob_VT]

Re: Another Which prop for me question.

Try to raise the outboard to the next hole and have the plate slightly above the transom. Just watch the water pick up.

 

[iwombat]

Re: Another Which prop for me question.

There's no way to raise the motor w/o drilling more holes in the transom.

 

[iwombat]

Re: Another Which prop for me question.

Open mouth, insert foot.

Memory is a funny thing sometimes. I thought I was adjusted all the way up, when in reality I was adjusted all the way down. So, I drug out the lift and set it up for 1" above the bottom of the transom. I'm out of town this weekend, so I'll have to wait until next week to see how much difference it makes. I still think I'm probably over propped still, but maybe not as much as I thought.

 

[iwombat]

Re: Another Which prop for me question.

Well, I tried it out and raising it up. It made no difference in RPMs and dropped the top speed down a bit, so back down a notch it goes. I think I'll be trying the 13-1/4x17 spare I have next time I'm out and go from there.