cavitation plate on larger motors

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lakegeorge

Senior Chief Petty Officer
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Mar 19, 2002
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660
When you run your boat at a faster speed can you see your cavitation plate? I'm not sure how far under the water it should be.
Mercury's web site claims that the higher your motor the faster the boat will go, you just need to make sure that it's not to high.
I don't see mine when I'm running my boat, it seems buried under water.
 
kfa4303

kfa4303

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Re: cavitation plate on larger motors

Hi lakegeorge. Generally speaking, you want the cav plate/anti-vent plate to be level, or slightly higher than the keel of the boat. The anti-vent plate should just barely break the surface of the water when at speed. It helps if you can get someone to carefully look over the stern while underway to see exactly where the plate is at speed.
 
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lakegeorge

Senior Chief Petty Officer
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Mar 19, 2002
Messages
660
Re: cavitation plate on larger motors

Thanks for the reply, that's exactly what I thought. I have the boat at the dealer waiting for my playpen cover to be installed and I asked them to measure it for me.
Merc people told me it should be 1" below the bottom of your boat when out of the water.
 
kfa4303

kfa4303

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Re: cavitation plate on larger motors

1" below the keel is a bit low, but the sweet spot is probably between its current height and about 1" above the keel. At worse, having the motor sit a little low in the water will create excess drag, but it's probably minimal and hard to notice on a 'toon. Regardless of the exact height, the main point is to be sure that the motor has plenty of water cycling through it at all times. Unfortunately, there's really no magic formula to get the best set up, just lots of trial and error until you find what works best most of the time.
 
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Outsider

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Re: cavitation plate on larger motors

Merc people told me it should be 1" below the bottom of your boat when out of the water.

The higher the motor, the less drag, too low and it's more drag. But too high and 1) you can start to lose cooling water, and 2) the prop blows out in turns. I've always found minimally acceptable performance when the cav plate is very slightly above water level at WOT. I've also determined that level with or an 1" or so above keel level to be the place to start. Only a water test can be the final arbiter ...
 
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