# Anti-cavitation plate above water line



## sea1blue (Apr 12, 2013)

I have a 2000 Pathfinder 15T. Just installed a Honda BF50A. I have a Honda 3 blade stainless prop 11 inches dia. and 13 pitch. I noticed that my anti cavitation plate measured 2 inch above my tunnel. It's slow to get on plane even with tabs fully down. With WOT the anti-cavitation plate is above the water line. The motor is at it's lowest setting. Is there a product to lower the required 2 inches. I know a jack-plate is designed to raise the motor, but what is available to lower a motor?


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## Recidivists (May 9, 2011)

http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1370742468/0#0

http://www.vancemfg.com/Drop-Down-Plate.html


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## topnative2 (Feb 22, 2009)

what goes up goes down!


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## sea1blue (Apr 12, 2013)

Yep, Drop down plate.. That's what I need.. Couldn't think of the proper phrase for the product needed..


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## Dillusion (May 21, 2012)

the cav plate being 2" above the water line wouldn't cause the performance problems you are experiencing unless you are severely cavitating and trying to launch in aerated water from the tunnel.

The last two tunnel hulls I have owned worked just fine with the cav plate 2" above the tunnel...what do you think a jack plate would do?

If you are experiencing 'slow to get up on plane' youre probably propped wrong.


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## sea1blue (Apr 12, 2013)

I'll install a tach this week to see what kind of RPM's I'm turning. The motor seems to run great once I'm on plane, even thought the plate is out of the water, but like I mentioned there is probably a 2-3 seconds of initial cavitation, then I'm up and raising trim tabs. Matt, I knew I would be searching for the right prop, any suggustions?


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## cvilt (May 31, 2010)

My 15t took a while to get up and go also. It sounds the same. It was powered with a 25 Yamaha and a four blade stainless prop. The four blade gives more lift Once it got up it was fine. I hear it is normal for that hull


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## Dillusion (May 21, 2012)

> I'll install a tach this week to see what kind of RPM's I'm turning.  The motor seems to run great once I'm on plane, even thought the plate is out of the water, but like I mentioned there is probably a 2-3 seconds of initial cavitation, then I'm up and raising trim tabs.  Matt, I knew I would be searching for the right prop, any suggustions?


You need a prop with more cup, it sounds like the prop that came with your new honda isn't the best for a tunnel hull.

I had this same problem on my shadowcast, I would open the motor up too fast and it would cavitate for a few seconds before it grabbed fully. Once I added more cup it ran perfectly.

I would not install a 'drop down plate'...I would instead look into either going to a prop shop and having them cupy our prop or ordering a new prop with the proper cup for a tunnel.

A four blade might help you as well.

As long as your water pressure is good and your motor is pissing fine, then the heigh it is at now above the tunnel shouldnt be a problem with the right prop.


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## sea1blue (Apr 12, 2013)

Pickings are pretty slim in the Panama City Area for cupping a prop. The motor didn't come with a prop, I purchased it from Honda. The Sale Manager a Pathfinder mentioned that they previously put a 10 3/8 dia, 13 pitch prop on 40 HP Yamahas. I'll buy a new prop, just unsure as to which way to go. Currently configuration pisses fine in both pressure and quantity. Wouldn't a higher pitch prop cause more cavitation or does it bite more allowing for greater lift and acceleration? The 25 HP Yamaha I took off, cavitation plate was even with the tunnel top. I'm definitely not smarter than my fifth grader..


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## Dillusion (May 21, 2012)

The prop characteristic I am talking about called "cup" has nothing to do with the pitch or diameter of the prop. Your prop may very well be a good match for the weight and length of the skiff, but just needs a cup added to it or more aggressive of a cup than it has now.

A prop cup or cupping is the bend on the trailing edge of the blades like shown here:










That little bend radius helps the prop bite into the water.


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## mirrocraft (Apr 29, 2009)

I had the same problem with my Boggy  Creek Tunnel. Last week I was sick of the cavitation. Took it to Ellis Propellor in Jacksonville.  Told the man what I was experiencing. I am using. Solas 13.25 x 17" pitch 4 blade on my 50 ETEC. He added cup and it changed the boat. Getting 33 miles an hour and keeps bite throughout acceleration. From what I have found with several props over the last 65hrs. With a tunnel a 4 blade with heavy cup is the best fit. Lifted the stern and does not drop on hole shot. Cost me $40 and 3 days downtime to add cup to the prop. Start there.


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## sea1blue (Apr 12, 2013)

So, what I'm hearing, is 4 blade prop, higher pitch and cupping should do the job? I was looking at the Power Tech website. They show a SWC4 prop. They indicate its excellent for tunnels and cavitation prone applications. It comes in 10.75 Dia and 10-15 pitch and 4 blade stainless. Would anyone recommend the 15 pitch with cupping..


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## Creek Runner (Sep 1, 2011)

You need a tach 1st to determine the RPM's your are currently turning. Then you will be able to make an educated decision on where you need to go. 

I agree with Matty, don't think your motor is to high just propped wrong. Cup will help, and once you have an RPM you can see where you need to go.


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## sea1blue (Apr 12, 2013)

Thanks all.. I'll keep you in the loop...


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## LWalker (Aug 20, 2013)

> Pickings are pretty slim in the Panama City Area for cupping a prop.


A little late here, but Marine Wheels in Southport at the Miller Marine Facility can work the prop for you. They have done lots of work for me in the past and they are very good at what they do.


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