Motor height or prop?

[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.

 

[hardwater fisherman]

Re: Motor height or prop?

maybe drop the tilt pin down one notch. also you may try shifting some weight around in the boat.

 

[carpking]

Re: Motor height or prop?

maybe drop the tilt pin down one notch. also you may try shifting some weight around in the boat.

I'm only in the second hole on the tilt pin. Moving it down a hole will put the motor directly against the transom and the angle will be off. Already tried shifting weight. Doesn't make a difference. Once the boat planes, this occurs. In the search section, people talk about the prop having a "spun hub". What does this mean? My prop appears to be all one piece.

 

[midcarolina]

Re: Motor height or prop?

Does the boat get on plane in a reasonable amount of time? It could be a prop issue or it could be a hull issue/design causing dirty water for the prop........

 

[hardwater fisherman]

Re: Motor height or prop?

to check for a spun prop make a line from gearcase to the prop and run it until you experience your problem. and then check the line. if it stays in line the prop is ok. if the prop is spun the line will no longer line up.

 

[steelespike]

Re: Motor height or prop?

Is the prop from 1975? It's possible a new prop may solve your problem.
Props do wear especially in heavily silted water. Modern technology is very likely better than the original.
There is a slim chance mounting the motor an inch or so off center left or right.In an attempt to reduce disturbance from the kneel.