Should I change prop pitch/ go to stainless.

[rkX4TR]

I am going to be adding a jackplate with 6 inches of setback to my setup. My current setup is a 15-foot v haul, with a 115 merc tower of power, 19 pitch aluminum prop. Currently turning around 5000 rpm. This is a bit low right now, but that should come up with the jackplate height. Currently experiencing some chine walk at 50mph, im worried the jackplate will make this worse. Im wondering if a prop change might help, or maybe trim tabs are the way to go. I know its going to be hard to give advice withought me having any feedback yet with how the jackplate handles. But thanks in advance.

 

[jimmbo]

I really don't see the purpose of adding a Jackplate on a small V Hull, but it is your choice. Raising the Engine often reduces Chine Walking. I am assuming you have the inline 6 115. WOT Range is 5000-5500rpm.
One thing to keep an eye on is, making sure the Engine is not being starved of Water when raised up. That goes for high Trim Angles.
A properly selected SS Prop, is often better at raised Engine Heights, than the AL props

From 1984 to 1998, I had a 15ft V hull with an 84 115, It came with a 19 Al Prop, and turned 5500, in 1985 I put a 19 Mercury 19 SS and it turned 5500, but had better bite on the water in turns. Engine was on transom but raised 1 3/4"

 

[Chris1956]

Have you checked the accuracy of the tach or speedo? It would be hard to get to 50MPH on a 19" pitch prop @ 5KRPM, I would think.

If you try 21P prop and can still get 5KRPM, you should be closer to 50MPH, IMO.

 

[rkX4TR]

Have you checked the accuracy of the tach or speedo? It would be hard to get to 50MPH on a 19" pitch prop @ 5KRPM, I would think.

If you try 21P prop and can still get 5KRPM, you should be closer to 50MPH, IMO.

the tach is old, seems accurate but i guess I cant know for sure. the speedo is a new gps model.

 

[Chris1956]

Do you have a 2::1 gear ratio on that engine?

 

[jimmbo]

With the 19, mine was turning 5500 and the speedo was reading about 49-50mph.
The I6 115 used 2:1 from 72 on. In 71 it had 25:14 ratio according to the Brochure(could be a Typo though)

 

[Chris1956]

Here is prop slip calculator. It may help.

https://www.mercuryracing.com/propellers-overview/prop-slip-calculator.html