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Jackplates on Offshore Boats

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Old 08-09-2011, 09:10 PM
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Default Jackplates on Offshore Boats

I was wandering if anyone had any experience with jackplates on a pair or more of outboards?

Better performance, speed?

I have a 33 Ocean Hawk with twin 250's and wandered if it would make a difference.
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Old 08-09-2011, 09:30 PM
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I was wandering if anyone had any experience with jackplates on a pair or more of outboards?

Better performance, speed?

I have a 33 Ocean Hawk with twin 250's and wandered if it would make a difference.
Twin 250's Where are your water pickups? 33 Ocean Hawk is a stretched 30 Corsa hull.
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Old 08-09-2011, 09:43 PM
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Lower unit water pickups

Where'd you get the Corsa hull thing?

Not what I've heard.
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Old 08-09-2011, 10:25 PM
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probley so . but u will need lower water pickup on them to get full benettfit of the jack plats. check out www.bobsmechine.com he use to make so bad plats for hulls like yours .
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Old 08-09-2011, 11:02 PM
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Lower unit water pickups

Where'd you get the Corsa hull thing?

Not what I've heard.

You will need low water pickups like 1fan said,The Hull thing ,from the Plug hull!
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Old 08-10-2011, 07:06 AM
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Getting back to your original question as to I jack plates help, let me offer some of what I know. I run Bob’s Machine Shop 8” setback manual jack plate on my boat and have had similar plates on several previous boats. The theory of a jack plate is that it will gain you two things:

1) It will allow you to raise the gear case in the water and thus reduce drag while under way
2) It will give the motor more leverage to lift the bow

The first benefit – less drag – is usually the thing that gains you the most speed since drag reduces speed. One has remember that simply raising the outboard mounting height on the transom (moving it up a set of holes) might give you a bit of this benefit without adding the jack plate. One also has to remember that water – as it breaks off the transom – comes up on an angle. So when you throw setback into the equation, if you run the motor at the same height, just further back, you’ll gain leverage but loose speed. (Because you’ve actually increased drag.) So as you go back, you need to go up – just to stay even. You only reduce drag when you beat that curve.

The other important point (made by others here) is that you need to be careful about how high you go so as not to lose cooling water to the motor. Generally speaking, raising the motor up on a jack plate requires one to convert to some sort of low water pickup system. The only way you’re going to know how high you can go without modifying pickups is to have both a water temperature and water pressure gauge on the dash for each motor.

One thing you may want to consider is maneuverability around the docks. As you raise the motors up, you end up with the props in water that’s less dense nearer the surface. Less dense means you’ll move the water with the props, but not have as much effect on moving the boat. And, the water you are moving (especially in reverse) is just blowing up against the transom. In a high performance boat, we’re generally willing to trade something off for speed. In a recreational boat, you may not like the tradeoff.

Finally, if you do decide to either move your motors up on the transom or add a jack plate and experiment, remember to seal the holes in your transom carefully. If you don’t, water will get into the wood inside the transom and cause all sorts of problems down the road.
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Old 08-10-2011, 08:18 AM
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I run the "Porta Bracket" with my V8 Johnson"s hanging off the back. It is the best solution I have used. They did change one thing for my brackets, they made a stainless steel "wing nut" for the top of the hydraulic cylinder rod instead of aluminum.
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Old 08-10-2011, 01:41 PM
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[QUOTE=mrv8outboard;3474837]I run the "Porta Bracket" with my V8 Johnson"s hanging off the back. It is the best solution I have used. They did change one thing for my brackets, they made a stainless steel "wing nut" for the top of the hydraulic cylinder rod instead of aluminum.[/QUOT thats the bracket i was thing about but could not rember the name . thanks robbie
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Old 08-10-2011, 04:23 PM
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Depends on what you are looking for.. Yes a jackplate will enbale to to lift the motors , reduce drag and go faster... It could also throw off the center of gravity of your boat making it ride different , which may or may not be a bad thing..
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Old 08-11-2011, 10:47 PM
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Lots of good info so far, thank you all.

My motors are mounted on an Armstrong bracket and set to the highest holes. Problem is coming out of hole you get cavitation until getting on plane, just have to continuously throttle back until full planing and cavitation stops. Motors are also mounted as close together as possible.

Then it seems you can only trim so much before 'arching/trimming' to much and begin to deplete performance.

So what I'm thinking is adding jack plates would allow lowering motor mounting back down. This way you will still have manuevarabilty around docking, get on plane better then raise motors rather than trimming. I guess I'd also be able to run in shallower water.

Please explain what type of water pickups you need. I have low water pickups now, I guess, factory units. If having to water lower units also then the idea begins to sound worse.

I guess I also just want to run a rooster tail.
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