Question About a Jack Plate

My jon boat with my 5hp Merc travels at 14.6 MPH(on GPS) in the highest slot of the bracket. And the lower is goes, the slower it goes. Once the boat reaches the mark of 14.6, the throttle is still not all the way. If I give it more throttle, it seems like it's blowing out or something. It spins the prop faster but the boat actually slightly decreases in speed. I've noticed that the cavitation plate on the motor is pretty close with the bottom line of the hull. But, the motor is sitting at an angle where the front of the cavitation plate is actually pointing downward. I was wondering if I was to fab up a jack plate, would this improve the speed and/or performance at all? I know there's not much I can expect from a 5hp, and the speed is actually pretty good. But it annoys me hearing it rev really high and not move. People have even questioned why the boat does that when they've test ridden it about a possible purchase. Fabricating something up shouldn't be a problem. I just would like to know if it'll help, to know if I should invest a couple dollars in materials and get to work.

 

If I tilt it on the stock bracket one slot lower, the boat goes 12mph. And the cavitation plate is actually lower than the hull. That's why I figure if I make some sort of lifting bracket, I can straighten the angle of the motor and possibly get a little better performance out of it.


I planned on keeping this boat to fish West Lake down in the park, and pond hopping. But I'm short on cash, so it's up for sale to finish my project skiff. If I can finish my skiff without selling the jon boat I'll keep it.