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How high should the cavitation plate be?

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  • How high should the cavitation plate be?

    Putting my boat back together. How high should my cavitation plate be, in relation to the bottom of the boat. It will have hydraulic tilt on it. Is this good enough or should i go higher? It is as low as it will go right now. ThanksClick image for larger version

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  • #2
    Re: How high should the cavitation plate be?

    That's a pretty good start. It isn't really based on the level vs the bottom of the boat, it's more based on the depth of it in the water while on plane. You want a sifficient amount of water covering it to avoid cavitation (actually, it's called an anti-cavitation or anti-ventilation plate), but not so deep it causes drag. The tilt/trim helps quite a bit. Find that sweet spot of higher speed and the lowest RPM and you're good to go.
    2001 Carver Voyager 374 'Stick's Competition'

    Something tells me I should be on the water....

    If I answer your upholstery questions, it's only because I've been doing it 20+ years...

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    • #3
      Re: How high should the cavitation plate be?

      Should be even or an inch or two high from bottom of boat. How does she run? Do you have cavitation?
      16' Starcraft Restoration
      http://forums.iboats.com/boat-restor...on-589808.html

      - Pete

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      • #4
        Re: How high should the cavitation plate be?

        That looks a tad low. Probably even or just above the keel is correct.

        At WOT the cav plate should be riding just ON the water not plowing thru it. Too low and there's too much drag.....too high and you'll ventilate and possibly overheat because no enough water will be getting into the intakes.
        1975 Starcraft SS-16' / 1977 Evinrude 75hp now w/ CMC power trim and tilt
        17p prop- 36 mph @ 5900 rpm ( 2 people, 12 gals fuel, 2 batteries)

        1975 Starcraft Super Sport- Resto currently "in progress"
        http://forums.iboats.com/showthread.php?t=547770

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        • #5
          Re: How high should the cavitation plate be?

          Your bottom has irregularities that will prevent you from coming up as high as a slick hull would allow. It will cause turbulence in turns and cause the engine to ventilate; rpms increase and speed decreases. You may be about right where you are. If you don't have power trim with the tilt you mentioned, it is not as critical. You move the tilt rod in/out till you find a hole where everything works "pretty good" and leave it there. Back in '72 I had an 18' tri-hull with a 125 Johnny and had no trim, but I did have a SST prop like you have. I found a hole that allowed me to run 41 mph with a boat full of family and water ski 2 at a time to boot and we had a great time.

          HTH,
          Mark
          If you are new to boating or have a new boat, a knowledgeable friend could show you how to operate your boat and save you a lot of grief, maybe some money, and maybe your life.

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          • #6
            Re: How high should the cavitation plate be?

            It is different for every boat and you really need to play with it to find the right height, go all the way up and see how it runs, if it blows out too soon drop it a hole and try again till it doesn't blow out.

            I ahve mine set to where I have to trim down a bit in corners or it will cavitate but in a straight line it is perfect, raising the engine si is the easiest free speed there is, you can gain a good bit just doing that.
            GO IRISH!!!!

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