Motor too short?

[carpking]

I have a 1975 25hp Evinrude short shaft installed on a 15 ft fiberglass boat. The cavitation plate sits almost precisely level with the bottom of the boat. When the boat planes out, the plate is just under the surface of the water. I seem to be pumping plenty of water as well. However, occasionally the motor will rev up as if the prop loses traction. This is worsened by choppy water. I worry about damaging the motor so im currently not able to run wot due to this. I thought about notching the transom a couple of inches but I eventually want to get a bigger motor for the boat. I cant afford a jack plate at the moment. Im just wondering if this is a height problem or a prop problem.

 

[MikDee]

A Dole fin may help keeping the water at the prop, so it doesn't blow out.

 

[carpking]

The more I read, its very possible it could be a spun hub. The prop is dinged up. Also, I have a few extra props on some old parts motors. When I compare them, the current props hub seems to jut out on the prop nut side and seems a little crooked. Ill do the test with current prop and then try the others. The boat is a tri-hull design from front to back. The plate is level with the bottom center "point" of the hull. I suppose this could create some rough water going into prop as well. From everything I read though, it seems to run just where it should at plane. The plate is just under the surface and im still pumping plenty of water.

 

[Docksidemarineservices]

Post a close up picture of your prop. Chances are the prop is cavitating.