Propeller Cavitation

[Marlin275]

I was changing the drive peg position on the 270 Volvo to get more hull out of the water by going to the outermost peg.

57mph at that peg
53mph at middle peg
50mph at peg closest to transom

At the outermost position I noticed that the prop would cavitate in some turns and over some waves. Stainless steel prop.
I pulled power back to correct this but was left wondering if this is a serious problem or not? If I leave the drive in this spot with periodic cavitation will this do harm to prop or engine?

[olredalert]

-------Someone will probably give a better description but when your prop is cavitating its not getting a bite on the water and consequently is over-revving your motor (if all ready at full speed). Over-revving is never good for any part of the drivetrain. I would think that the sudden shock of getting bite again would also be hard on things in a somewhat relative way................Bill S

[MOP]

I think you have Ventilation, that is caused by over trimming and sharp turns. It is different than Cavitation which causes burn to the prop edges or surface. There are some very good articles on the web about it.

Phil

[gcarter]

I agree w/ Phil. It's probably ventilating.
Cavitation is a condition where the blade archetecture, boat speed, and propellor speed is such that vacuum bubbles form at the propellor blade trailing edge. The vacuum bubbles will actually pull molecules of metal from the blade surface.

[MOP]

But Red is 100% right about the strain put on the drive train when it hooks up.

[Marlin275]

I read 10 sites on ventilating, and that's what it is.
It really only happens when getting on plane or sharp turns at slower speeds never at WOT.
The only way to stop it is to pull back the power so it seems like it would not cause big problems?

[gcarter]

IMHO, the problem is caused because you don't have any intermediate steps in your trim, i.e., you're over trimmed but you don't have any alternatives.
So you can bury the prop deeper and go slower, or go faster and ventilate.

[kjly63]

Marlin, I know exactly what your going thru :frown: . I run an Ultra 24 LH in the top notch with no problem at 5600 rpm and 59 mph WOT. I just tried a SS chopper prop this w/e and found major vibrations at low speed and cavitation. Once I apply some gas the props grabs and the top end is about the same with 600 rpm less. I tried it in the middle notch and found too much of the hull is in the water........lost 4 mph. I did notice no torque at all at WOT........as if I had power steering :lookaroun
All in all the best prop so far is the Ultra; gonna send it to a prop place in CT. to add some cup to see if I can drop the rpm's a bit. :outtahere

Ken