Twin yamaha F115b propeller question
 

Hi, i was just womdering if somebody have made this change and how it affected the performance of the boat?
Also what prop were you using and what are you using now?
Mine were 13 x 19 3 blade painted ss and i just ordered a couple of PowerTech RBX 15 P 4 blade. Would i imrove in the performance of the boat?

You are dropping a LOT of pitch going from 19p props to 15p props.

just plug the numbers in to the prop calc . . . boat setup is pretty straight forward. Once you get the engine height set right and weight distributed in the boat. Finding the right props is just math + a small amount of voodoo.

Pitch is number of inches your boat moves forward per rotation of the prop.

19p = 19 inches
15p = 15 inches

You have some slip . . . usually less with 4 blade props or large diameter props, but generally around 10% for recreational boats.

Gear Ratio on the f115 = 2.15:1

Prop Calc
http://www.go-fast.com/Prop_Slip_Calculator.htm

What was the max RPM with the 19's?

http://www.go-fast.com/images/speed.gif
http://www.go-fast.com/images/SlipForm.png

Mine calculates to 16% slip. Is that too high? Do I have the correct prop?

3 blade alum x 17 Pitch

It's perfect, if you want to make sushi out of those Shell Crackers and Stump Knockers, Jim.

Yeah Jim, all you have is a "cheapo" prop!! I couldn't resist :) As Terry says the 17p aluminum prop will chop up those pan fish faster......unless you have introduced it to rocks!!

Donny, you know those aluminum props are good for those who are "Bathymetrically Challanged", like Jim and me. Sometimes I've been known to navigate by Braille!!!
Smuggle some of that Apple Pie into MacRae's and we'll get this all sorted out.

There we go again in the wrong website Latitude - we'er supposed to be down on "Gatherings" with this discusssion.

Only truly competent captains dare go with aluminum. It's not about economy, it's about confidence. Red on Right when Returning...LOL!

16% with that prop is perfect for digging clams.