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Motor to transom height.

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  • Motor to transom height.

    I just bought a 2008 ultracraft 14ct with a df25 suzuki 4 stroke. I have a 20" transom and a 20 inch leg. the vent plate is about 2 inches below the bottom of the boat. Is this why there is so much water splashing up off the back of the boat? I also get the warning light coming on at full speed. as soon as i slow to idle the light goes out and i can take off again..... Is this because of overspeed due to ventilation/cavitation? I dont have much room to raise the motor on the transom... Any adjustments on the motor itself??

    Thank you.


  • #2
    Re: Motor to transom height.

    The ventilation plate should be even with or a little above the bottom of the transom. Yes, it can splash water in to the boat if it is too low. If you can not raise the motor on the transom, you will probably need a jackplate. Your warning light could be many things. Do you know that it is coming on because of overspeed? Put a tach on it and see what speed it is running. If it is revving too high, first fix the motor height and then re-test it. If it is still running too fast, you can get a prop with more pitch to slow the motor down.

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    • #3
      Re: Motor to transom height.

      After measuring more carefully, It seems that the leg is actually 22" this is why the VA plate is 2" below the boat.
      Can you recomend where i might get a plate or bracket to gain this 2 - 2.5"?
      Thank you.

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      • #4
        Re: Motor to transom height.

        Depending on how much room you have from the top of the transom to whatever device secures the motor to the transom you may be able to put a 2" piece of wood/whatever on top of the transom to raise it.I doubt that the way it is setup is causing the warning light to come on,otherwise the PO would have dealt with it.Purchased from a Marina ? then it should be covered and set up properly.
        Cool Runnings,,, Mr.88

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        • #5
          Re: Motor to transom height.

          Could it be the prop? I checked and i have a 10 1/4 by 10. Suzuki website says that motor comes stock with a 10 1/4 x 11 ????

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          • #6
            Re: Motor to transom height.

            Proper transom height is important for good performance. A motor mounted on a transom that is too high causes the propeller to slip resulting in wasted power or overheating. A motor mounted on a transom that is too low will increase drag, causing reduced speed.

            Make sure that when the motor is lowered all the way down, the anti-cavitation plate is located 0 -25 mm (0 - 1.0 in.) below the bottom of the boat.

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            • #7
              Re: Motor to transom height.

              the 10" prop is just one size up from the lowest pitch here at iboats.If you and your boat are light it could be over reving.But get your height solved before trying to pick a prop.
              just throttle back to limit rpm.You will need a tach and a gps for speed to tell where your rpm is.If you motor has provisions for bolting to the transom you may be able to raise the motor
              without worrying about the clamps.A jack plate will allow an accurate height.Just be sure the setback is enough so the clamp handles clear the transom if necessary.
              If the po ran heavy loads a lot they may have propped for that.

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              • #8
                Re: Motor to transom height.

                Correction on usm's post. As stated by wifisher, you want the anti-ventilation plate to be above the keel. Even with is ok but best is 1" above or so. You don't want it dragging in the water when the boat is moving. The water should be coming from under the boat and "up", pressing against the bottom of the plate. If the plate is below the keel, it can actually pull the stern down when you are moving, causing lots of drag and making the boat handle funny. Plus it will throw water up in the air as you mentioned in your post. Is the engine mounted in the highest holes? A fixed jack plate may be the fix and they're not terribly expensive.

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                • #9
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                  Re: Motor to transom height.

                  Have been trying to figure out why engine OEM's build a 22" skeg when they know full well transoms are 20". I guess they do it for work boats and high thrust applications where the prop has to push a lot of water and the water moves more than the boat moves and it helps to prevent ventilation. Course for normal applications you can always jack it up on the transom whereas the converse would be a real burden.

                  My 2c,

                  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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