24' with 115 Johnson speed concern

[leinad55]

I have recently purchased a 24' Princecraft with a 20" - 115 Johnson. Both 2000 models. The previous owner had just added the 115. It came with a 70 and he said it would only run about 15 mph and he couldn't pull a tube. He had added a 14x13 prop. This prop ventilated badly. I added a hydrafoil and it only made it worse. I pulled the hydrafoil and put on the spare prop, a cupped 13-7/8x11. It works great with no ventilation or cavitation but the boat only runs 15 mph @ 5800 rpm. WOT is 6000 with this prop and that's the last 1/4 throttle but no increase in speed. I know if I want to go fast I should have a speed boat but the 115 should push it faster than 15 mph.

My question, what prop should I be running on this boat?

Thanks for your help.

 

[EGlideRider]

Re: 24' with 115 Johnson speed concern

First, is the speed measured by a GPS. I can get 21 from my 24' with 115 with a cupped 14X13 and I have a permanent rear enclosure that acts like a giant sail. You may have a REV Limiter that is limiting your R's to 6K. You might consider a prop like mine.

 

[leinad55]

Re: 24' with 115 Johnson speed concern

Thanks, EGlideRider. I should be able to get my 14x13 cupped at the local prop shop.
Looking at the picture, is the prop deep enough in the water, and if not, where should the prop be setting in relation to the bottom of the toons?