Antiventilation/anticavitation Plate Rhetoric (Trivia)

[Texasmark]

I was raised to call the plate on top of the prop an anticavitation plate. Some time ago, on here, I was corrected and told that it was an antiventilation plate.

Did some checking on the definition of the two and agreed with my mentor that I should be referring to it as antiventilation. So, that's what I started adding to my definition.

So here I am last night ,surfing the old Merc sites and run across an ad for their tilted motor they developed back in the '60's when Mercs were white. It's the one they said solves the trolling problem where fuel puddled at the rear of the cylinder so they tilted them up as they did with the whole engine.

Sure nuf, in big bold black print, they were defining the different parts of the engine and the plate was ID'd as anticavitation.

Must be where I got the ID. 8)

Mark

 

[JB]

Re: Antiventilation/anticavitation Plate Rhetoric (Trivia)

Once you understand the difference between cavitation and ventilation the purpose of the plate becomes obvious, Mark.

Now if we could just get them to call them outboard engines.8)

 

[Paul Moir]

Re: Antiventilation/anticavitation Plate Rhetoric (Trivia)

What we know now as the anti-ventilation plate was invented by Warren Cordon at the Johnson Outboard Company in 1922. And there is little question of it's original name: the anti-cavitation plate. Referring to Lou Johnson's 1923 patent (1,467,641),

The lower end of the tubular member 1 is provided with a horizontally disposed plate 47, which prevent cavitation, especially when the device is being used on the gunwhale of a the boat

Naturally, the trouble caused was not by cavitation but rather ventilation of the propeller although some of the effects are similar. Ventilation occurs when air is sucked into and trapped by the propeller, causing it to slip in the water stream. Cavitation, rather, is caused by extremely low pressure areas often created by the excessively fast movement of an object through water. The effect is to cause the water to boil and implode local to the low pressure area.

Clearly, the plate prevents the former.

The misnomer was apparently widely corrected in about 1936, although I don't know for certain what caused the correction. Older service literature often refers to it as the "anti-ventilation plate" after that date.

Patent 1467641
The Johnson Story
Sear Horse K-30 diagram referring to anti-cavitation plate

 

[Texasmark]

Re: Antiventilation/anticavitation Plate Rhetoric (Trivia)

Thanks guys, and JB you are correct. Once I read the definitions I knew I was wrong........but I've been wrong all my life about it :% 8)

Mark

 

[imported_HammerHead1]

Re: Antiventilation/anticavitation Plate Rhetoric (Trivia)

excellently described Paul