Cavitation Plate Set Up
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Cavitation Plate Set Up

  1. #1
    Large Member edog's Avatar
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    Default Cavitation Plate Set Up

    My boat had a problem with porpoising and bucking. No matter what position I had the place diverter set at. It had plates mounted on it from the factory, the were not adjustable and were 2" off the transom, and they were 2 degrees down. So we made longer plates that are adjustable with turn buckles. I am not sure how long they should as you can see from the photo's we left em a little long. They are going to be set at 1-2 degree's up to start. Not really sure where to start with a set up.





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  3. #2
    Owner/Crew Chief 1/4 Miler's Avatar
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    Length of the plates?

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    Senior Member hihosilver's Avatar
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    you might want to add a plate on the transom as there is a lot of pressure on the turnbuckle

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    Glendale Arizona Squirtcha?'s Avatar
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    I had a set on my last boat. Had to put them on for the reason you stated. I started with them even with the bottom and dropped them a turn/rotation at a time then went and ran it. Once I found the adjustment that made the porpoise go away, I started to take them back up a little at a time until the porpoise came back. Made notes and put them right where it wouldn't porpoise.

    In other words it was pretty much a trial and error deal. You don't want them too low to where they're scrubbing off speed. Just enough down to make the porpoise go away.

    The length looks o.k. My boat porpoised really bad and the plates fixed it completely. They were shorter than the ones you have there too.

    How's it going Jak?
    Last edited by Squirtcha?; 02-08-2010 at 07:35 PM.

  7. #5
    Large Member edog's Avatar
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    Quote Originally Posted by 1/4 Miler View Post
    Length of the plates?
    They are 10" off the transom.

  8. #6
    Large Member edog's Avatar
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    Quote Originally Posted by Squirtcha? View Post
    I had a set on my last boat. Had to put them on for the reason you stated. I started with them even with the bottom and dropped them a turn/rotation at a time then went and ran it. Once I found the adjustment that made the porpoise go away, I started to take them back up a little at a time until the porpoise came back. Made notes and put them right where it wouldn't porpoise.

    In other words it was pretty much a trial and error deal. You don't want them too low to where they're scrubbing off speed. Just enough down to make the porpoise go away.

    The length looks o.k. My boat porpoised really bad and the plates fixed it completely. They were shorter than the ones you have there too.

    How's it going Jak?
    Thanks for the info. I am completly frustrated with the porpoise. I am happy to see you were able to get yours under control. Gives me a litle hope. I plan to shorten the plates, and add some supports to the transom. Today was just a trial run to see if could get any adjustment.

    When you adjusted yours a turn do you remember how far the plates moved? I know each application will be different depending on how far out your turnbuckles are mounted, but it will give me an idea and something to compare mine too.

    Thanks

  9. #7
    Glendale Arizona Squirtcha?'s Avatar
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    It's a pretty fine thread so they don't move a whole lot on a turn. When I got mine set to where they worked best, I could lay a straight edge along the bottom (including the plates) and see about an 1/8" of space.

    Mine was really bad so I'm betting it'll take care of your problem.
    Last edited by Squirtcha?; 02-08-2010 at 08:56 PM.

  10. #8
    Large Member edog's Avatar
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    Quote Originally Posted by Squirtcha? View Post
    It's a pretty fine thread so they don't move a whole lot on a turn. When I got mine set to where they worked best, I could lay a straight edge along the bottom (including the plates) and see about an 1/8" of space.

    Mine was really bad so I'm betting it'll take care of your problem.
    This thing was pretty bad also. At cruising speed if I did not have the Place Diverter all the way down it had an annoying porpoise. On the top end it would start to buck with the place diverter all the way down, and there was no way in hell I had any chance of moving the the diverter up.

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    Just Me snoc653's Avatar
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    Is that an Eliminator simi-v? If so the porpoise doesn't come from the plates but from the spoon in the hull. Read Propless' thread when he had his.

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    Senior Member propless's Avatar
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    edog, like Squirtcha posted try about 1/8" down to start, if the porpoising is gone then bring them up 1/4 turn at a time until it starts again them drop back to where it was. You want the highest setting you can get away with, having them down will kill speed really bad. Also, how much fuel is on board and how many people are in the boat (weight distribution) will change what the boat wants you to do with the plates. You just need to find a happy compromise, or put a handle on them.

    BTW, You also mentioned "On the top end it would start to buck with the place diverter all the way down". Mine did that too, dont do that. The hull is trying to lift and the diverter angle is trying to keep the bow down, its fighting itself and hopping. Mine would hop 3 or 4 times then launch completely out of the water. Believe it or not, as soon as I brought the diverter up (a little above center) and stood on the throttle the boat would take a good set and work. Diverter down to cruise, and slightly up when you get on it, at least thats what worked for me.

  13. #11
    Owner/Crew Chief 1/4 Miler's Avatar
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    edog,

    What you've essentially done is extend your hull's length by 8 inches, 10 inches of the plates now vs. 2 inches originally.

    First, I would hope that the hull extention plates are set in a 'recess' such that they do not hang down deeper than the glass of the hull (meaning they are absolutely flush like plates on a flattie) and that there is no significant gap between the bottom glass (either in front of, or on the sides) and the plates as either of those things will cause significant disruption of water flow (turbulance) and deter handling. Secondly, I would imagine (?) that the reason for the original 2 inch plates @ 2 degrees down were to put a slight 'hook' in the bottom for better handling than the hull's design without them provided ..... just a thought as I've heard of builders doing this type of things on other hulls.

    If I were you, I'd start out at 0.00 degrees on the plates (relative to the hull bottom side angle), in other words, a straight extension of the hull and go ever so slightly down angle from there if 0.00 doesn't yeild the results you want ....... remember that the longer the plates, the less amount of turns on the turnbuckels it takes to put the tips of the them down the same amount ....... for example, the original 2 inch plates @ 2 degrees means the tips of the plates were below the hull 0.0690 inches and if you put the 10 inch plate at 2 degrees, they would be 0.349 inches below ..... a drastic difference which could not be healthy to say the least.
    Last edited by 1/4 Miler; 02-09-2010 at 05:47 AM.

  14. #12
    Owner/Crew Chief 1/4 Miler's Avatar
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    Dan ...

    Just hanging in there trying to figure our Race Program this coming year ... Hope all is well with you and yours.

    Jak

  15. #13
    Large Member edog's Avatar
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    Quote Originally Posted by snoc653 View Post
    Is that an Eliminator simi-v? If so the porpoise doesn't come from the plates but from the spoon in the hull. Read Propless' thread when he had his.
    It's made by Daytona.

  16. #14
    Large Member edog's Avatar
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    Quote Originally Posted by propless View Post
    edog, like Squirtcha posted try about 1/8" down to start, if the porpoising is gone then bring them up 1/4 turn at a time until it starts again them drop back to where it was. You want the highest setting you can get away with, having them down will kill speed really bad. Also, how much fuel is on board and how many people are in the boat (weight distribution) will change what the boat wants you to do with the plates. You just need to find a happy compromise, or put a handle on them.

    BTW, You also mentioned "On the top end it would start to buck with the place diverter all the way down". Mine did that too, dont do that. The hull is trying to lift and the diverter angle is trying to keep the bow down, its fighting itself and hopping. Mine would hop 3 or 4 times then launch completely out of the water. Believe it or not, as soon as I brought the diverter up (a little above center) and stood on the throttle the boat would take a good set and work. Diverter down to cruise, and slightly up when you get on it, at least thats what worked for me.
    Right now it's a two seater. We tried not having an ice chest, full of fuel, no fuel, two people, one person. It didn't matter. I had no way to adjust the plates before. I will try what you said on the top end. I might try to test it this weekend.
    Last edited by edog; 02-09-2010 at 07:15 AM.

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