Prop size and pitch ?

[Hogsters]

I have a 1996 24' smoker craft pontoon boat with a 90 hp mercury. How do I figure out the best/recommended prop size and pitch.

 

[jerryjerry05]

Re: Prop size and pitch ?

You need a tach. Run the boat at WOT and note the rpm.that motor should run about 5400-5600 WOT.What size prop is on the motor now? Take the reading and get back with the results.Jerry

 

[Hogsters]

Re: Prop size and pitch ?

At WOT it is hitting right around 5000 rpm. I have noticed a bit of cavitation at 3/4 throttle thru WOT. I don't know if this has to do with the power tilt adjustment or the prop size/pitch.
I can't find any markings on the prop to determine the pitch of the current prop. Are they normally marked in a cercain spot.
For the size do I just measure across the prop outside of fin to outside of fin.

 

[steelespike]

Re: Prop size and pitch ?

On a 3 blade measure from center of hub to tip of a blade then double.
Generally diameter is a product of the prop design so if the prop is listed for your motor it should fit.The diameter may vary from yours.Sometimes prop numbers appear on the hub near where the nut goes on.If you can't find numbers a prop shop can measure it for you.You should be able to adjust trim to limit Ventilation(sometimes in correctly called cavitation)
If you are at 5,000 a 2 in decrease in pitch will increase rpm about 200 rpm per inch.netting about 5,400.