Jack Plate

[The Job Site]

I have a 1990 Mercury Black Max 200hp. My question is should I get a stationary jack plate to raise the motor up to not have so much prop down below the boat. Right now I have a 23 pitch prop and she takes a while to plane and my trim after I get running will not trim up to well. Only to a certain point. Then I have to slow down and trim up then start again with trim up high to get Faster Knts ????

[RidgeRunner]

That prop is too much for a v-20 for sure. I have a 200 Merc on my 20 but it will not even spin a 19 pitch to my liking. Running a prop with too much pitch will not allow the motor to turn the proper RPM at wide open throttle. At WOT your motor should be turning 5500 to 5800 RPM. You need a tachometer and a GPS to figure out your optimal setup. You will find that your speed will actually increase with a smaller pitch prop, it will come out of the hole like a rocket and your fuel consumption will go down.
A jack plate would allow the motor to turn the 23 to the proper RPM range at WOT, however your hole shot is not going to get any better and you will be slipping the prop hardcore to accomplish what amounts to trimming the edges off the square peg to make it fit into the round hole. High mounting height may also require a low water pickup be installed to maintain water pressure. The flat plate(anti-cavitation or just cavitation plate) just above the prop should be even with the top of the water while on plane (ie even with the bottom of the boat or perhaps an inch above works fine.)
Trim pumps on the Merc are two stage. From the fully tucked position the smaller trim rams (2) move to give the operator the ability to trim the motor and raise the bow while underway. Then at a real high trim angle the longer hydraulic cylinder takes over to tilt the motor all the way up. The tilt portion (the longer cylinder) is not strong enough to hold the motor up while underway so the motor will ease back down to the fully trimmed position on the two shorter trim rams. If your trim will not work with the hammer down the trim is faulty. Check the wires going to the pump to see if you may have a bad connection or corroded wires. If the trim pump motor isn't turning the motor should be rebuilt or replaced.
With the motor mounted correctly on the boat I don't think you could get your Merc with a 23 pitch prop to turn 5800 RPM with the motor trimmed all the way out. It would probably blow out and loose MPH first.
Install the tachometer first than go out and try a 17 or 19 pitch prop.
Hopefully you haven't damaged the engine with the 23 pitch. There is a very good chance for engine destroying predetonation when you lug a two-stroke engine.
Opinions vary on these forums but I have been rigging boats for a long time. I have a prop you can try if you are close.
My .02 -- Good luck -- VIC

[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

[spareparts]

check your tach, you should not be able to hit 7000 with a 23 unless teh prop is cavitating. My 79 has a 84 200 merc and came with a 21P quicksilver stainless prop. I have had a chance to run it since I bought it, but it had been run that way since the engine was bolted on the transom in 84

[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%.