Whats an anti cavitation plate?

[75-JOHNSON]

probably a dumb question, but what is this? does my 1976 75 HP Johnson have one?

 

[tx1961whaler]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

Yes. It is the horizontal surface just above the prop. Also called an antiventilation plate

 

[75-JOHNSON]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

Thank you very much. does this have to be level with the bottom of the boat when the motor is 90 degress to the boat?

 

[nate1220]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

it depends on how you have your motor trimmed.

 

[Bob_VT]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

It is best that the motor is mounted on the boat so that plate is even or about an inch above the keel.

 

[75-JOHNSON]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

If it is trimmed ALL the way down.. trying to figure out if i need to move the engine up or down.

 

[75-JOHNSON]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

It is best that the motor is mounted on the boat so that plate is even or about an inch above the keel.

And the keel is the lower-most part of the boat at the back? (my boat is a fibreglass trihull)

 

[nate1220]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

bob your from castleton, I live in North clarendon

 

[nate1220]

Re: Whats an anti cavitaion plate?

Re: Whats an anti cavitaion plate?

when the motor is trimmed all the way down the cav. plate should be flush or up to 1 to 1.5 inches above the keel (the lowet partof the hull or the rib running down the center)

 

[NSBCraig]

Re: Whats an anti cavitation plate?

Not trimmed all the way down but parallel.

 

[Chris1956]

Re: Whats an anti cavitation plate?

The plate above the prop on an I/O or Outboard is an antiventilation plate. Calling it an anticavitation plate is incorrect.

Cavitation is different than ventilation. Ventilation is when air gets to the prop. The AV plate stops that ventilation.

Cavitation is caused by low pressure or vacuum behind the trailing edge of the prop. Ofter, it erodes the metal of the prop, due to the boiling of the water and other forces..

 

[75-JOHNSON]

Re: Whats an anti cavitation plate?

ok so i moved the motor up a bit to get the "plate" at a better level. Now exactly what will this do for me? will the effects be very noticable or not?

Note: previously the antiventilation plate was about 1.5 inches below the keel of the boat when trimmed down. now it is about 1 inch above the keel.

 

[JB]

Re: Whats an anti cavitation plate?

You will now have less drag, which should be noticable at planing speed.

Once you have the boat on plane, trim it out until rpm peaks but short of prop ventilation or boat porpoising.