Jackplate/motor question?

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confused1234

Cadet
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Aug 31, 2010
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How far up or down should the motor be on a jackplate? When you look at my boat from the side with the motor down, the center line of the prop is about even with the bottom of the hull. Is this too high? It seems like I am running way too many RPM's for the speed. I am turning 4000 RPM's only getting about 35MPH(24ft Bay Champ 250HPDI). I just got the boat from somebody so I am not sure where to set the jackplate/motor hight???
 
tashasdaddy

tashasdaddy

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51,019
Re: Jackplate/motor question?

it depends on how far back the jack plate sets the motor. 1 inch higher for each foot of set back. it sounds like you are way high. RPMs and MPH do not really relate.

you want to set up the motor so that it runs at optimum RPMS, at WOT. this includes weight and style of the hull, set back, height, and proper propping.
 
metriccrescentwrench

metriccrescentwrench

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Oct 22, 2007
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2,598
Re: Jackplate/motor question?

It depends on your boat and the setback. Also, when setting up a boat with a jackplate it's important to have a water pressure gauge.

Just as a reference, on my 18-1/2 ft Checkmate with 200 Johnson I've got a 6" jackplate with the prop centerline 3 inches below the pad. Other guys with nearly the same setup run about 2-1/2 inches below the pad.
 
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Dhadley

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Feb 4, 2001
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16,978
Re: Jackplate/motor question?

The motor height depends largely on your prop's technology. That's true if you have a jackplate or not. There is no one measurement that's the ultimate for all boat / motor combos. You can have 2 identical boats with the same motor with the same prop that are balanced different and have different X dimensions.
 
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confused1234

Cadet
Joined
Aug 31, 2010
Messages
8
Re: Jackplate/motor question?

Is this jack plate setting too high? This is where the previous owner had it. It looks kind of high to me but I am not sure. Any help?
 

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Dhadley

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Feb 4, 2001
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Re: Jackplate/motor question?

The AV plate looks to be about even with the step in the transom, looks like about 6" or so of setback. Can't tell much about the prop itself other than it's a 3 blade stainless. Again, depending on the technology built into the prop it could be at the optimum height for that combo. My guess is that it shouldn't go any lower.
 
NSBCraig

NSBCraig

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Aug 21, 2007
Messages
1,907
Re: Jackplate/motor question?

That's pretty close.

You have to factor in the setback of the plate. (I've always used 6" setback per 1" up using the AV plate as a guide not 1' like TD said)

And the built in setback of the hull. That's what the transom notch is for, in fact most boats with a notched transom don't need a jackplate except for when running way skinny water.

So I'd start with setting your AV plate 2" above the very bottom of the hull and see what that gets you. Then try up an inch and down an inch. Just make sure you have water pressure so you don't cook your motor.

From there it's all about the prop like Dhadley said.
 
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