Cavitation Plate?

[Mister]

Can somebody explain what a "Cavitation plate" actually is :-?

[marto78]

A cavitation plate is a permanent horizontal plate on the vertical shaft of the outboard right above the propeller. It sits just at the water level when the boat is up on plane (ie: flush with the bottom of the boat, for a planing style hull).
It prevents 'cavitation' of the propeller ie: prevents air from the surface of the water being picked up by the action of the propeller. Cavitation drastically reduces a prop's effectiveness & efficiency; basically a cavitating prop is pushing some air rather that just water. Over-revving can also result.

Read more: http://wiki.answers.com/Q/What_is_an_outboard_motor_cavitation_plate#ixzz1lY EtLz2x

[Crunchy]

Ohhh, I thought that was a foot-step to help me get back into my boat

[gofishin]

Actually marto, that definition is not correct – but it wouldn’t be the first time for Wikki! ;)

The correct name for this ‘plate’ is an ‘Anti-ventilation plate’, to prevent/reduce ‘ventilation’, but it is very often incorrectly referred to as a cavitation plate – as cavitation and ventilation are also very often mixed up, even by experienced jurnos who should know better! They are also mixed up a bit on this site ;D

[gruntahunta]

A cavitation plate is a permanent horizontal plate on the vertical shaft of the outboard right above the propeller. It sits just at the water level when the boat is up on plane (ie: flush with the bottom of the boat, for a planing style hull).
It prevents 'cavitation' of the propeller ie: prevents air from the surface of the water being picked up by the action of the propeller. Cavitation drastically reduces a prop's effectiveness & efficiency; basically a cavitating prop is pushing some air rather that just water. Over-revving can also result.

Read more: http://wiki.answers.com/Q/What_is_an_outboard_motor_cavitation_plate#ixzz1lY EtLz2x


I am pretty sure mine is well under water at plane or anytime....no way my motor is trimed that far back to have it at the water level?

[FishHunter]

Its actually suposed to be slightly above the water at cruising speed if its in the water is causes all kinds of issues.

[gruntahunta]

Its actually suposed to be slightly above the water at cruising speed if its in the water is causes all kinds of issues.



Ok....thats something to have a look at next weekend...ur prob right Fishhunter...but that means the top of the prop is only about 1/2 to 1 inch (12mm to 25mm) in the water if it is level with the water. This prob explains why cavitation happens in foamy waters.

[marto78]

Actually marto, that definition is not correct – but it wouldn’t be the first time for Wikki! ;)

The correct name for this ‘plate’ is an ‘Anti-ventilation plate’, to prevent/reduce ‘ventilation’, but it is very often incorrectly referred to as a cavitation plate – as cavitation and ventilation are also very often mixed up, even by experienced jurnos who should know better! They are also mixed up a bit on this site ;D

You say tomatoes and I say 2martos, but we both know what we are talking about ;D::);D

[Peter4]

If you search "cavitation plate" on this forum you will quickly realise that Mister is simply a cheeky bugger fishing for responses...

[Crunchy]

I'll play that game....

According to my yahama owners manual I only have an "anti-cavitation" plate:(. Would I install the anti-ventilation plate above or below the anti-cavitation plate?:P
Thanks

[marto78]

If you search "cavitation plate" on this forum you will quickly realise that Mister is simply a cheeky bugger fishing for responses...

Yes he is.

But for anyone else that wants to know the difference between cavitation and ventialtion:


"CAVITATION: Even slightly chipped or bent blade edges can cause surrounding water to BOIL ("cavitate"). Gas bubbles then condense elsewhere on the blade, releasing energy that causes metal erosion or "cavitation burn".
"VENTILATION: Air from the water surface or exhaust gases from exhaust outlet being drawn into the prop blades causes ventilation. This reduces normal water load, causing the prop to over-rev and lose a lot of thrust.
Ventilation is most common with high transom mounting, extreme trim-out and sharp turns. Mercury props are designed to minimize ventilation." So, summarizing, cavitation is from damaged blades, and ventilation is mostly from high mounting, without a prop that can handle it.
To get rid of ventilation, you generally have to either drop the engine down, or use a surface piercing performance prop.

[FishHunter]

Ok....thats something to have a look at next weekend...ur prob right Fishhunter...but that means the top of the prop is only about 1/2 to 1 inch (12mm to 25mm) in the water if it is level with the water. This prob explains why cavitation happens in foamy waters.

I picked up a couple of hundred rpm and the boat was much more responsive to engine trim once I got the cavitaion plate out of the water at cruise if you do a google on setting motor hight or search here you will find some pics of what it should look like,

[Fed]

According to my yahama owners manual I only have an "anti-cavitation" plate:(.
Just because it's written in a Yamaha manual doesn't make it right.

You don't want to be raising your motor gruntahunta, light buoyant tinny probably with an extruded keel needs all the grip it can get.

A point of interest, Mercury who would be on the cutting edge of prop design & setup carried out test which indicated a speed gain of 1-2 MPH @ 80 MPH for every inch raised so it's hardly worthwhile from a speed point of view in a fishing boat.

[stue2]

Check this link out. all you need to know about motor height and cavitation. If the motors are in the water too far they can cause the boat to porpoise, you have less trim control, more drag.
If the motors are a bit too high they can pick up a bit of air from time to time but i'm told that this is better and can be controlled with a bit more cupping on the prop.

I lifted the motors on the vag 2 holes and completely changed the boats performance. Added trim tabs and performance/control stepped up as much again. No real gain in speed, dropped the revs about 100 - 200 rpm.

It was well worth the effort to get this right

http://www.veradoclub.com/smf/index.php?topic=137.0

[Crunchy]

Just because it's written in a Yamaha manual doesn't make it right.

You don't want to be raising your motor gruntahunta, light buoyant tinny probably with an extruded keel needs all the grip it can get.

A point of interest, Mercury who would be on the cutting edge of prop design & setup carried out test which indicated a speed gain of 1-2 MPH @ 80 MPH for every inch raised so it's hardly worthwhile from a speed point of view in a fishing boat.

I rang Ya*#@a Japan about this and their reply was:

"Hurro Clunchy, Fed-san tlake this too sleriously, beside we make motor so we can call it whatever the fluck we want. Merc%ry gaijin scum, whether anti-claviatation plate in or out of water engine still plerform like brick, fine tuned great japanese motor top performance with anti-caviation plate out of water".

So there you have it straight from the horses mouth

[The Woo]

Pressed tin boats often cannot have the plate (yep, I'm just calling the the plate :p) as high as glass boats.
This is because of the "keel" and the underwater shape of the tin boat. As I say, often the tin boat's engine needs to be a little lower to get the prop into clean water, especially during turns, and often than means the Plate is fractionally underwater.

[Fed]

I rang Ya*#@a Japan about this and their reply was:

"Hurro Clunchy, Fed-san tlake this too sleriously, beside we make motor so we can call it whatever the fluck we want. Merc%ry gaijin scum, whether anti-claviatation plate in or out of water engine still plerform like brick, fine tuned great japanese motor top performance with anti-caviation plate out of water".

So there you have it straight from the horses mouth
HaHaHa!
You're the man Crunchy, too funny mate.