Is this normal?

[LegacyT]

This prop only has around 10 hours bought brand new this summer. The burning is on all 3 blades in the same spot. Seems to me to be excessive for such low hours...

 

[Alwhite00]

Re: Is this normal?

That is from cavitation and the "frosting" is from cavitation bubbles forming and imploding on the surface and taking small pieces of metal off of it. Blade shape is not perfect for speed that is causing this cavitation.

LK

 

[mpsyamaha]

Re: Is this normal?

looks like excessive cavitation to me, specially in only 10 hours. Have you ever tried punching your numbers in on a prop slip calculator? I bet there is a better prop out there for your application, hopefully someone with more knowledge can make some suggestions.

 

[steelespike]

Re: Is this normal?

Cavitation can be an indication a prop is working very efficiently.
I have a Mercury prop from a 65 merc. 500 with about 40% of the back of the blades is heavily "burnt"
Obviously has lots of hours.I have another that has about 10% burnt much less hours
I have a 3rd that is lightly used is developing burns 1/8" x 1/2" Newest prop on the boat has started to get burns in the exact same way.
These are all Merc props.11" and 10".One changed do to age one changed because it got dinged the third changed to try a 10"
The motor is properly set up on a 18ft 57 Crestliner bare utility since 1965.
All up weight is about 900lbs.
I'm the second owner and have known the boat since new.The original owner was very particular and must have felt the first prop was running well.The boat was used to haul goods from the main land transport people and gear.
Spent many years as a fireboat worked several fires over the years and was used every fall for duck hunting.
I guess my point is cavitation burn is normal.
I guess we could tell more about it if we had your light load wot rpm and gps speed.
Also the details of your setup. setup.

 

[LegacyT]

Re: Is this normal?

The prop is Michigan Match 14x21, basically identical to OEM. The boat RPM at WOT with a light load is 4400 rpm @ 48mph on gps. Right in the the middle of the 4200-4600 rpm WOT range. Rpm was verified using a shop tach with an inductive pickup. I just thought it wouldn't burn so quickly. How long can you run it before its time to repair? I'm worried that its burning at the roots so badly and potentially throw a blade at high rpm...

 

[steelespike]

Re: Is this normal?

Could you tell us what hp and gear ratio your Volvo is?
I'm sure not a cavitation expert but based on the props I have in hand I think failure from cavitation damage is highly unlikely.
Something to consider is the quality of the paint job.My oldest prop obviously has many hundreds of hours on it
and pretty severe "burning"You could feel it in the dark. The paint on the thrust side of the blades is untouched except for the actual tip edge of the blades not the thrust surface.All the props are oem and the thrust sides are the same condition.
I don't know if it's from a quality paint job or the relatively clear St lawrence water.
You might consult with Michigan wheel.They have been helpful using their archives to identify some old 40s,50s bronze props.
They surely could tell you if your burning is unusual for that prop.
What is the burning like on your old prop?

 

[LegacyT]

Re: Is this normal?

The boat has 230 hp and the gear ratio is 1.61:1. I checked the slip on a calculator and it came out to 12% which isn't bad... The Michigan match even has the identical Volvo part # stamped into it and is powdercoated. The hull doesnt have any external fittings that could cause ventilation. Maybe thats just the way it is...

 

[Texasmark]

Re: Is this normal?

I had a 1971 85 hp Chrysler with a stock alum prop. The prop had a reverse twist emanating from the root at the front of the prop similar to the black alum prop at the top of this forum but more exaggerated. Frank, in the Force engine forum knows what I am talking about.

It burned the paint off in a circle on the pressure side of the blade (yours is on the ebb side) about the size of a nickel coin almost immediately, and over the short season I used the boat it kept eating into the blade. In time one would expect that it would eat right through it and then what? Expand it's area possibly. Don't know. I never had another prop with that distinct leading edge and never had a prop that showed cavitation damage.

One with damage as long as yours would surely ultimately eat through the root of the prop enough to possibly result in a lost blade and who knows what kind of damage.

Have you thought about a SS prop?

Mark