looking for the cavation plate

[57lawney]

been gone awhile,sorry for the dumb question. i have a 93 40 hp.johnson am looking for the cavitation plate, is it the one with the bolts thru it or the one above it? locally i have gotten both places,just trying to get new to me motor set up to the boat. thanks ron

 

[chriscraft254]

Re: looking for the cavation plate

been gone awhile,sorry for the dumb question. i have a 93 40 hp.johnson am looking for the cavitation plate, is it the one with the bolts thru it or the one above it? locally i have gotten both places,just trying to get new to me motor set up to the boat. thanks ron

(Bold print) What? The cavitation plate will be the one right above your prop. Will have a trim anode on the bottom of it.

 

[Chris1956]

Re: looking for the cavation plate

Actually the horizontal plate above the water intakes on the gearcase is the "anti-ventilation plate". I presume that is of what you are speaking. No such thing as a "cavitation plate" on an outbaord.

 

[kfa4303]

Re: looking for the cavation plate

That's right Chris 1956. Cavitation is a bad thing, so there isn't a plate that encourages it to happen. Rather, there is an anti-cavitation plate to prevent it from happening. Here's a pic of an outboard (my '61 10hp) with the plate circled, but they're in the same place on all motors. Hope it helps.

 

[Chris1956]

Re: looking for the cavation plate

That plate is an anti-ventilation plate. Without it, the prop could suck in some air from the surface of the water and ventilate.

Cavitation is altogether a different thing....

 

[coleman kayak1]

Re: looking for the cavation plate

Yes, technically the plate you are referring to is known as an anti-ventilation plate.

A Anti-Cavitation plate, commonly known as a cavitation plate, is required on certain configurations. It attaches, most often with bolts, to your anti-ventilation plate, and as mentioned, prevents cavitation or the sucking of air into the prop

Hope this helps

 

[kfa4303]

Re: looking for the cavation plate

uhhhhhh........so I'm confused. The anti-vent plate prevents and the anti-cav plate both prevent the prop from sucking in air (OK sounds good), so doesn't that mean they're doing the same thing? As I understand it, cavitation involves boiling of the water at lower pressure (due to an influx of air) which can, in turn, weaken the prop and/or cause pitting, whereas ventilation is just the general phenomena of air being sucked into the prop area.?.?.? Neither of which are desirable, of course. Just want to use the proper terminology going forward. Thanks.

 

[coleman kayak1]

Re: looking for the cavation plate

Sorry I should have been more clear.

All motors have an anti-ventilation plate. You are correct on the purpose it serves.

An Anti-Cavitation plate, however, is an aftermarket piece of equipment. It is required on certain configurations, for example my pontoon used to cavitate when going around corners at any speed.

They DO the same thing, but you usually only have an anti-ventilation plate, not an anti-cavitation plate.

 

[chriscraft254]

Re: looking for the cavation plate

lol, Some of you guys make things harder than they have to be. Here is another diagram for the op.

 

[wellcraft19]

Re: looking for the cavation plate

Cavitation and ventilation are two totally separate things...

Cavitation: due to lower pressure on the "forward side" of the propeller, the water can start to boil, introducing air bubbles. Very bad, can pit a propeller quickly.

Ventilation: Propeller is (for whatever reason) sucking air from the surface, loosing grip (think of it as whipping cream with an electric mixer)

If you want a "stabilizer" (as in post #6) to put on your anti-ventilation plate (they can be useful under certain conditions), I have a brand new Stingray someone can have for cheap.

 

[kfa4303]

Re: looking for the cavation plate

Gotcha. Thanks for the clarification.

 

[Chinewalker]

Re: looking for the cavation plate

Cavitation has nothing to do with ventilation. Case in point - a submerged submarine's screws (props) can cavitate during extreme maneuvers and acceleration - hundreds of feet from the surface. As Wellcraft 19 pointed out, it's bad for the props as it can make the surface very rough over time. Also makes a lot of noise, which in a sub isn't always a good thing....

 

[57lawney]

Re: looking for the cavation plate

so this is the part that needs to be even with the bottem of the boat?

 

[kfa4303]

Re: looking for the cavation plate

yes, or even slightly higher than the keel. Here's a handy pic/diagram.

 

[Joe Reeves]

Re: looking for the cavation plate

Lighten up people... that plate has been referred to as an cavitation plate even back before I started in this line of work (1960). The important thing is that we know its purpose. If I want or do not want ventilation, I'll open or close a cabin window. (grin)

 

[Chris1956]

Re: looking for the cavation plate

Joe, Gee, can't we use the right term? I would like to think we have learned something as a group in the last 51+ years (smile)

 

[wellcraft19]

Re: looking for the cavation plate

We should probably also blame the manufacturers who, unfortunately, often are referring to it as as "cavitation" plate.

Now, does anyone want my "Stingray"?

 

[Joe Reeves]

Re: looking for the cavation plate

Joe, Gee, can't we use the right term? I would like to think we have learned something as a group in the last 51+ years (smile)

Chris.... Why sure, you betcha. Now just the other day I found out that what I thought was an outboard is actually a kicker (grin).

 

[fshrgy99]

Re: looking for the cavation plate

Hey Wellcraft! what model is the stingray 'hydroplane' ))and does it come with a bolt free installation kit?

 

[wellcraft19]

Re: looking for the cavation plate

Not bolt free. My anti-ventilation plate was drilled when I took it off. Think I still have some photos after I pulled it off.