cavitation test?

[Thinqer33]

I've got a collection of banged up props from over the years. I've gotten most in pretty good condition but want to know how can I cheaply test whether or not their cavitating? I heard that spraying paint then seeing if it wore off was one way to go but seems the leading edges always lose their paint. Tips?

 

[steelespike]

Re: cavitation test?

Cavitation occurs on the under side of the blades.You don't feel it.The water boils in the low pressure areas of the underside of the blades.
It will erode the surface where it occurs.Usually only cosmetic.Cavitation can be an indication a prop is working very well.
You can see the effects of cavitation on the underside of the blades.
I think your referring to "ventilation".Ventilation occurs when the prop gets fouled with air.The motor revs and the boat usually looses speed. Which are you referring to?

 

[Texasmark]

Re: cavitation test?

Frank A. on the Force forum can show you pictures but I had a '71 85 hp Chrysler (Force predecessor) that had an OEM wheel with a reverse pitch on the leading edge. It continuously burned the paint off the top of the blade in a circle about the size of a quarter just aft of the detent just off the root at the front of the blade.

Mark

 

[walleyehed]

Re: cavitation test?

It's been my experience that true "cavitation" causes blade burn which shows up very similar to what my ole' buddy Mark is saying...It tends to slowly erode the paint (and later, can erode the prop material itself) but it tends to show up on the aft face of blade about 1/3 of blade length away from hub, somewhat centered in the chord of the blade. Steelespike may have a similar thing going on and may be seeing something I haven't but when I do see this, the majority of the time it has been an improper application issue, ie, trying to do one thing with a prop that was designed to do something else-or "excel" in another area.

 

[Texasmark]

Re: cavitation test?


Hey man, where you been? Missed your inputs. For those reading that don't know this guy he is "Mr. Prop". Glad you're back. Looks like you upgraded your equipment while you were gone. Nice.

Mark

 

[steelespike]

Re: cavitation test?

I have 3 Merc props from a 65 Merc 500.tiller Run on a stock Crestliner 18' short deck Bucaneer utility.Toriginal prop
is white I believe the number is 48-38098 11" It was used extensively 5 years?Severe cavitation burns starting at the root
of the blades covering about 1/3 of the blades The scound prop is black 48-38098 11" Much less used as it appears he dinged 2 blades
and replaced the prop early. Cavitation erosion had started near the root of the blades about 1\2" wide and 2" long
The 3rd prop is a 48-38094 12" Used just enough to lose as little strip of paint about 1/8 X 1" at the root of 2 blades.
He went back to the 11" presently on the boat.
All three props have one blade with obviously less erosion.Also there was no paint loss on any of the props thrust side.
It's very possible he used a tach as I know he had a shop tach and loved to fiddle with his boats and motors.
And he was fussy about things.