Should I remove my jack plate?

jsaylor

Petty Officer 3rd Class
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Jun 20, 2011
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I have a procraft 1750 (bass/skiboat) with a 1987 mariner 150, 6 inch jackplate. Here's my issues, have to tuck the engine all the way down otherwise it will porpoise until at least 40 MPH, would not be possible to run without my dolphin. Extremely difficult to hang on to the steering wheel, so much resistance. I have tried raising and lowering the jack plate with no change. Any ideas, or should I just remove? I can't tell if there are four bolts that hold the engine to the boat or just two on top, seems like it would be difficult access to the bottom ones.Thanks so much
 

wired247

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Oct 8, 2011
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I think I'd change props before I pulled the jack plate. Thats the source of your problem.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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sounds like you are using a bow lifting prop. I would also change props, or put the cooler of beer up front
 

Dukedog

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Might wanna try different motor heights to. Just don't get toooooo high. Watch your water pressure gauge. That boat shouldn't have that problem!
 

mr 88

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Did you buy this rig as is and if so have you talked to the previous owner about it ? Not saying your should ask for your money back ,maybe the guy has a answer or goes yes it did it and all I ever did was drive through it to a speed that it stopped or maybe tell you how he ran it and then take it from there.
 
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jsaylor

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Jun 20, 2011
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Have tried raising the engine, currently at 5 inches from center of prop to bottom of boat, I raised it up one inch and it seemed worse, perhaps I should try more than one inch? I'm using a trophy 22 SS, having a hard time getting out of the hole 4900 WOT, I just bought a 4 blade 19 Hustler aluminum, results are pulls out of the hole better WOT still 4900 but lost some top end, boat handles the same with both props. Seller of boat can't be located.
 
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wired247

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You have a jack plate and you are 5 inches below the bottom of the boat? What are you running ? A 25 inch motor on a 20 inch transom?
 

jsaylor

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I was informed to measure from center of prop to ground, then measure from pad (bottom of boat) to ground then subtract the difference, this value is 5 inches, I have been told however 3.5 inches is optimum. Center of prop is 9 inches to ground, bottom of boat at rear is 14 inches, all level.
 

wired247

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If your pad and motor are level then what you are saying works. You should be able to run the prop centerline 3-5 inches below the pad even without a jackplate though. A trophy is a medium bow lifting prop but if you don't have the power to push the prop it won't hold the bow and you'll porpoise. You generally don't have to bury those trophy's deep to get them to work. Try a lower (number ) pitch prop. A 4 blade 22 pitch with a heavy boat and a 150 is pushing it for being able to carry the bow. Try jacking the motor up to 0-2 inches under and don't trim over neutral. It won't carry the bow as high but you don't really need that.

FWIW I usually run most of my props 1 inch above the pad
 
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jsaylor

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I've gone from the trophy 22 to a 19 4 blade hustler aluminum, surprising not much change in WOT, a bit of a lose in MPH, prop is on exchange and I HAVE A couple more days to exchange, do you think I should try a 17 4 blade hustler? I do remember dolfins creating difficult steering, perhaps I should raise my motor and remove my dolphin? Thanks again for taking the time
 
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Dukedog

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Is tha trophy a big hub (14 1/2") or tha earlier small hub (13 3/4"). Being a 22 makes me think its tha later big hub, bigger blade. If so its a little much for tha little 2.0 motor unless you runnin' it as high as possible. Your rpm also says something to this effect. Goin' to a 19 alum. with not much rpm increase is also an indicator of something outta whack. Might get some disagreement but a tweaked 21/22 Laser would be something ya might try. That motor outta be turned at least 57/5800 ta get tha results you lookin' for.......jmo.If ya want I can send a PM with a site that tells ya exactly how (drawings) to get your motor height. Can't post it here.......
 
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jsaylor

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yes please send, EDIT yes it is a big hub
 
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jsaylor

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Jun 20, 2011
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I'm thinking of doing some more testing with engine height, should I do these test with the dolphin removed? I believe the dolphin could be my source for difficult steering.
 

Dukedog

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yes please send, EDIT yes it is a big hub

Yeah, too much prop. Shouldn't need any ACCESSORIES when it's right. PM sent. Lemme know if ya got it. This new format gives me fits sometimes!!!
 
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jsaylor

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Jun 20, 2011
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No Title

More confused! I read one way to set engine height as follows: measure center of prop to ground, then measure bottom of boat (rear pad) to ground, then subtract the difference, this equals 5 inches, I hear optimum to be 3.5 to 5. This is how it's currently set. Then I read the cavitation plate should be 1 inch to level with the bottom of the boat, I just took a look and my cavitation plate (the large one) is about 5 inches above the bottom of the boat. Besides the porposing and poor hole shot my concern is the heavy steering. Using the first technique I would most likely raise the engine, using the second I would lower the engine. See attached
 

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Dukedog

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Oct 6, 2009
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Tha only thing tha cav plate is good for is getting tha motor level. Its tha prop shaft center line that's tha concern. Very bottom, motor (at cav plate), and ground has ta be level.....Measurement taken from pad to ground. Measurement taken from center of prop shaft to ground. Difference is tha height. Should be at 3.5 inches ta start with..........Just like his drawings.....
 

wired247

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Don't believe everything you read. That anti-ventilation plate below the bottom of the boat thing applies to big displacement hull fishing boats or yachts. For lightweight boats that you want to plane fast , steer without a lot of effort and go fast you want the prop centerline to be MUCH higher and the anti ventilation plate to be completely out of the water when running.

Optimum height is going to be where you still have water pressure and bite on the water at takeoff. There is no magic number. Its dependent on your hull. 3-5 inches below the pad is sunk damn low. Don't be afraid to crank that thing up until you start to lose water pressure. You'll find your steering will improve dramatically, you'll plane faster, get better gas mileage and your dog will like you better.
 

Chris1956

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Mar 25, 2004
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First off, get rid of that whale tail. You can't need it, and it can cause difficulty. They are for butt-heavy or underpowered boats, of which yours is not.

If the boat porpoises at minimum trim, under 40MPH, the motor is too high. Drop it all the way down and retest. Gradually raise it up until it is optimum for your driving style. Remember the anode will counter torque steer. Your's is likely out of the water, and has no effect.

The hustler is a good prop and should work well. I would prefer a 3 blade one.

Let me know if it gets better....
 
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