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Thread: merc 4 stroke jet

  1. #1
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    Feb 2009
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    Default merc 4 stroke jet

    considering putting a merc 25 4 stroke jet on my inflatable,raised floor. they say it requires a transom of 20" on the 25 but does any one know what the actual dimension is from the top of the transom mount to the leading edge of the intake. i wont be installing a jack plate and want the shoe as high as possible,perhaps right on the surface? also,is there a perfect angle for the intake to meet the water? if the angle was decreased it would run shallower. it figure that on plane i would be able to travel safely in a few inches of water. anyone been there done that?

  2. #2
    Member Yukoner's Avatar
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    Aug 2007
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    Default

    Jet OBs on inflatables requires a bit of voodoo magic to get right. You will have to have a jack plate to get the motor up high enough, otherwise you aren't really taking advantage of the shallow water potential. If it gets too high, you will get cavitation. Best thing to do is take it out with some blocks of wood of different size, and play with the height until it just starts to cavitatae, then drop it back an inch or so. Hope this helps some.
    Never wrestle with a pig.
    you both get dirty;
    the Pig likes it.

  3. #3
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    Feb 2009
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    thanks, ive done the wood block thing with my prop motors,trying to get them to run as shallow as possible. my confusion is with the stated transom height (20")and where that places the jet intake.seems to me that it would be several inches below the bottom of the boat and not in the optimum position. all jet outboards with a 20" transom should have the same measurement, just wondering what it is and how high the motor has to be jacked to bring it up to the bottom edge of the transom.

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