I actually was hoping for about 18 - 18.5MPH I was surprised that it was only 17.1 MPH. My son had his Proboat Sundancer there and had run it for about 4-5 minutes. We put the GPS in his and it came up at 14.0MPH bone stock 7 cells gp3300 and after a little warm up laps so his probably would be about 14.5MPH from the start. I was really flying by him which gave me the impression it was faster than 17.1
On mine running gp3300 7 cells the motor was barely warm ( made a water jacket like Jan has come up with) on the Johnson 63706 drill motor. ESC was also barely warm and the batteries were warm but not hot. I moved the water pick up to the bottom of the boat as you can see from right before the rudder because the rudder assembly had pulled completely out from the extender yesterday. The water was shooting out a good 5-6 inched at good speed. The rudder assembly did start to pull out again - the holes for the screws are more striped than I thought (easy fix I hope) and the boat did it's 1st spin out ever. It never did that before and at high speeds it takes a big path to turn it around unless I slow down a bunch so I was surprised that I could get it to spin out.

Mocars, that big turn radius has alot to do with how far your rudder is mounted out past the rear of the boat. I knew the prop was the problem all along. Cavitation is usually caused by too many rpms for the size of prop. If the prop is too small for the motor then the prop will spin so fast the small blades wont catch water. A bigger prop will grab more water and get the boat moving.

Are you saying I should bring it closer to the prop than it is now? How much distance from the prop should the rudder be? It's now about an inch from the shaft to the rudder - too much?

I would say about 3/8" to 1/2". But lets see what everyone else says first. I am really not sure. But anyway I was talking about how far the rudder is from the back of the boat is what is making the turn radius large.