prop cavitation

[mymaria]

What is prop cavitation ? and how can it be fixed, i have a 75 searay, 5.7 thunderbolt with an a alfa 1 outdrive. i just installed a new prop.

 

[ziggy]

Re: need advise//W

Re: need advise//W

What is prop cavitation ?

definition
videos

w/o reading what i linked. cavitation is when waters pressure becomes so low that it boils (turns to gas, steam) in cold temps. the bubbles of gas turn right back to water and when the do it's like an explosion on the blade of the prop. thus damaging the metal.

if ya look close ya can see the pits. copy pic to paint and blow it up to see better.

these are photos of my prop. minor cavitation burn. i feel they likely come from minor imperfections in the out edge/dia. of my prop. prop dings.

if my understanding conflicts with the definition, i'd think the definition would be correct. not me.

 

[Texasmark]

Re: need advise//W

Re: need advise//W

I had an OEM aluminum prop on a new Chrysler 85 I bought back in 1971. The leading edge of the blades had an irregular shape right at the hub which caused a vacuum to form causing bubbles just behind the leading edge of the blade which ate first into the paint then into the alum as is the case in Ziggy's prop and I agree that nicks in tips of the blades could cause it. Mine made a circle about the size of a nickel.

Ventilation is not cavitation and is caused by the prop sucking surface air into the propwash. OEM's installed a horizontal plate called an "anti-vent" plate just above the prop which does a good job of combating the problem under normal circumstances. Normally no prop damage results from that and when it occurs, you loose "traction" if you will...some call this process Blowout.

Mark

 

[Frank Acampora]

Re: need advise//W

Re: need advise//W

Well, Mark, some may call it blowout, and yeah, I can see it as such, but the other definition of blowout is when the shockwave from the gearcase nosecone expands to larger than the prop diameter and the result is dramatic loss of thrust. It is strictly a high speed phenomenon that usually occurs only over 60-65 MPH and on blunt nosecones. That's why a lot of racers weld on a pointed nosecone extension.

 

[Texasmark]

Re: need advise//W

Re: need advise//W

Well, Mark, some may call it blowout, and yeah, I can see it as such, but the other definition of blowout is when the shockwave from the gearcase nosecone expands to larger than the prop diameter and the result is dramatic loss of thrust. It is strictly a high speed phenomenon that usually occurs only over 60-65 MPH and on blunt nosecones. That's why a lot of racers weld on a pointed nosecone extension.

But Frank, we are not talking about that 65 mph and shock waves and all. We are talking about when you trim your prop so far out that it tilts up in the air and starts sucking air rather than water....... We are talking about the average boating guru and his stuff and in my case the Chrysler "stuff" that I bought in years past of West Bend derivatives which wound up as Brunswick "Force Brand" with Phantom Black rather than "Sea Foam White" and all, and that stuff that you seem to love. Apples and oranges man.

Mark