Possible Ventilation?

[afrojojo]

The other day I was out I managed to hit a submerged log with my 25hp Johnson. Now, when im wide open, the motor gets louder right at the peak of top speed. It almost sounds like the exhaust gets lifted slightly out of the water.

The lower unit looks ok. There is a slight drop in top speed, the aluminum prop looks a little chewed up on all the blades, and two of the blades are bent back. Would the bent blades cause prop ventilation and disturb the surface water causing you to hear the thru-hub exhaust more? I ordered a new prop and am having this one repaired for a backup, but wanted to know what you guys thought.

 

[Outsider]

That might cause ventilation. Now, turn the key off, slowly back away from it, and do not approach it again until the prop shaft has been inspected and the propeller properly repaired. Damage has already been done, don't make it worse by trying to self-diagnose ... :facepalm:

 

[UncleWillie]

With chewed up and bent prop blades, you may be one of the few people that can make an actual claim to having Cavitation.
At full power the low pressure on the Front of the blades will turn to vapor and then immediately implode and collapse.

You will see pitting of the paint and metal on the Forward surface near the tips of the blades.
Ventilation will cause the Engine RPMs to jump up and over-rev the engine.
Cavitation may very well sound like the explosions of the exhaust. They are small but extremely powerful!

Many boaters mis-use the Cavitation term when they really mean Ventilation.
You may be the first one to reverse the trend!

 

[Sea Rider]

Cavitation, Aireation, Ventilation are the prop terms most used. When new prop is installed go for a close turn at enough throttle for boat to remain on plane on flat calm no wind waters. If achieving aereation, ventilation, engine revving up must sit engine lower on transom.

Hasppy Boating

 

[steelespike]

You may have broken a rubber engine mount,also the prop may be damaged enough to cause ventilation/cavitation though you seldom hear or feel cavitation.
You can get the prop repaired though a new prop may be more cost effective.Especially if your prop is old.
Remove the prop and rotate the shaft by hand. Hold a screwdriver or something close to the shaft to note any wobble.