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i saw an earlier post regarding this but my question is. looking at my boat yesterday on the trailer my 200 yam sea ox motor is mounted using the 2nd hole from the top and the cavatation plate is about 2 inches below the bottom of the boat where the drain plug is located when trimmed all the way down. is it worth the trouble to move the motor up one notch which is 3/4 inch difference.i do hit 5400 rpm wot.it just seems the 21ft w/a tops out about 34mph on the gps on flat water. i had a 19 prop on it originally in which i only got 5000 rpm. i now have a 17ss whis put me right at the maximum level.will i gain any speed lifting up the motor?
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Your motor is mounted on the second hole and the cav plate is still below the transom bottom?? It sounds like the boat is suppose to have a 20" shaft motor and somebody hung a 25" shaft motor on it. The cav plate (the plate just above the prop...) should be about 1/2 - 1 inch above the transom bottom, it should not be in the water when you're running on plane.
Mike -
Chris,
Mike is right - when you are up on plane and trimmed out for max speed, the cavitation plate should be running right on top of the water and not down in it - any higher, and the prop starts sucking air (ventilation), any lower, and you have unnecessary drag.
Good luck [img]smile.gif[/img] ,
Ken KComment
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I have a 20' Sea Ox w/a cuddy with a 150 Yamaha 4 stroke, 25" shaft, 14 1/2 x 17 aluminum prop; the boat taps out at 40 mph by gps; the boat has a closed transom with a 23" transom bracket; the cavitation plate is above the bottom of the keel; but from what I was told - because of the set-back bracket - you can't go by the rule of thumb which is cavitation plate even with the bottom of the hull. Have no cavitation problems & fuel economy is excellent with the 4 stroke. RPM is 5600 tapped out.
Good Luck... DTComment
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