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  Outboard motor height with jackplate on a 1985 Outrage 18

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Author Topic:   Outboard motor height with jackplate on a 1985 Outrage 18
tlynch posted 03-18-2003 03:02 AM ET (US)   Profile for tlynch   Send Email to tlynch  
Archie's question about his Montauk reminded me that I was planning on asking the same thing about my '85 Outrage 18. I have a 150 HP Johnson and will be installing a 9" fixed jackplate. What should the distance be from the bottom of the boat to the anti-ventilation plate on the outboard? I am not looking to use the boat in shallow water, but rather increase the overall performance of my boat. I will be using a 19" Pitch SS Viper Prop. I will not have a water pressure meter so I would rather be safe than sorry.

Thanks in advance,
Todd Lynch

Bigshot posted 03-18-2003 10:56 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
9" huh? I would go up at least 3" to start and bring tools with you. Keep going up until you get a slipping clutch reaction when you nail it from a stop. At that point you are pretty high and if you desire you can lower it some. I have mine setup so that I do not slip, not interested in speed or else I would have not gone with a 70hp.
lhg posted 03-18-2003 05:07 PM ET (US)     Profile for lhg    
When running a jackplate, what counts is not the ACP height above the hull bottom, but rather where the engine cuts the water when planing. This will vary based on setback and speed. For the kind of prop and estimated speed you will be running, you want about 1" height for the AC plate, above water surface. It usually takes some trial runs to find this place, which is why the jackplates have adjustable height. The greater the setback, the higher the engine will be relative to HULL bottom. That is why the full transom backets perform so well. The engines can be up as high as 5" above hull bottom, but still the AC plate is only 1" above the water flow past the engine.

You can measure your engine to determine the maximum height the engine will allow. Usually this is about 2 to 2 1/2 inches. If the top water intake hole begins to take in air, you're going to aereate the cooling water and overheat the top cylinders of the engine.

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