Jack Plate

[RidgeRunner]

Originally Posted by The Job Site

Wow thats alot of good information and thanks. I have a tachometer and she will hit almost 7000 rpm at 34 knts I have not checked the GPS speed.I also have the tail piece you are talking about on the motor. The guy I bought the boat had a 19 and had it replaced with this 23 due to not enough top end... he said a great hole shot but low top end. I will try a 19 and check the difference out. Thanks

Wait a minute. This is not adding up at all. My 1983 20' CC with the 200 Black Max will only twist to 5500 rpm with the 19x14.25" prop at about 39 knts.(44 MPH) Trimmed out with a light load. Same boat & motor goes 41.7 knts (48 MPH) with 17x14.25 at 6300 RPM. Faster with the 17 pitch but too many RPM. I settled on a 17x15.25 Mirage at 40 knts (46 MPH) 5800RPM --- Perfect
I am doubting your tach as the black max 200 Merc fishing motor should only be turning between 5500 and 5800 RPM. With a stock motor 7000 RPM is too high unless you have a highly modded 200.
I feel your tach is not correct. How many RPM do you show at idle? Perhaps the knob on the back of the tach is not set correctly.
How are you measuring your speed. You mentioned you weren't using GPS. If you tell me you are letting out rope and counting the knots as they go thru your hand I will probably knot be able to render any further assistance:)
Most dash mounted speedometers are only accurate to within +/-10MPH.
Depth finders with the paddle wheel are better but the GPS is DOBA.
Something is amiss. No way you are turning a 23 pitch 7000 rpm.
I plugged it into the prop slip calculator. Your speed would be 62 knts (72 MPH). Or your prop slip is over 50%.