Is it cavitation?

[bhammer]

More of a technical question.... I had always thought that cavitation was the formation of air bubbles in water due to pressure difference.

I see all these threads about cavitation. Wouldn't it really be ventilation, or is it cavitation? I would think that if your prop is too close to the surface it is ventilating and not cavitation.

 

[Tig]

Re: Is it cavitation?

You are correct. You'll find that many of those threads have someone making that same point.

 

[QC]

Re: Is it cavitation?

LOL, just made that point in Andy in NY's thread that probably prompted your question. Cavitation is caused by the pressure differential and the resulting formation of bubbles on the surface of the prop. The collapsing of the bubbles is quite destructive and leads to pitting of the surface where the bubbles form . . .

Take a look at the Inertial Cavitation and Cavitation Damage sections of this Wikipedia Article The other common place to see Cavitation Erosion is diesel engine cylinder walls. Every time the engine fires there is an expansion of the cylinder wall and then a snap back. The snap back causes the pressure differential and the associated bubbles and then the bad stuff . . .

 

[steelespike]

Re: Is it cavitation?

I have an old Johnson TD20 owners manual that refers to ventilation as cavitation.
never using ventilation.So I think its understandable that there may be some confusion on the terms.Cavitation probably used in error since the first outboard.
Did a little resrearch. Found a boating dictionary. Found only cavitate and cavitation in reference to props no ventilation even in reference to fresh air.One refers to bubbles forming near the tip as a result of a prop turning too fast,The other refers to prop turbulance in the water reducing prop efficiency.

 

[QC]

Re: Is it cavitation?

I've wondered about the history of that confusion. Thanks. I actually understood cavitation erosion from my engine career which started in '77 before I understood ventilation, which I learned when I bought my first boat in '84, so the misuse of Ventilation and Cavitation has bugged me ever since.

 

[180shabah]

Re: Is it cavitation?

so does the antiventilation plate prevent cavitation or does the anticavitation plate prevent ventilation?????

 

[steelespike]

Re: Is it cavitation?

How do you ventilate anything from underwater? lol.

 

[bhammer]

Re: Is it cavitation?

LOL, I think if you have a futzer valve attached the flux capacitor, you don't have to worry about either...

Thanks for the info. I was thinking I was on the right track between cavitation and ventilation. I agree with QC, I have seen some erosion on larger propellers due to cavitation. It is like many little explosions.