jack plates?

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shawnfish

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Dec 17, 2010
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i see some guys using them to set their motors back farther away from the transom and was wondering what the advantage was?
 
Supposedly, the further you set the motor back from the transom the higher you are able to lift it. Less motor in the water = less drag and higher speed.
 
My boat has a 15" transom and the motor is a longer short shaft mariner. I bought a BH mini jacker to raise the motor b/c my river is shallow. Now the anti-cavitation plate is at the correct height given the 4" set back.
 
There should be quite a few posts in here about jackplates that you can read.
First off..........there is no set rule about how high you can go vs how far back you are. Somebody in here will probably tell you that for every inch of set back you can go up 1/2". Not necessarily true at all.
Main reasons for these are to increase overall performance of your combination. Be it that you can run shallower, or faster, or gain bow lift, whatever you are after you can set the plate for.
You will have to either invest in another propeller or have yours sent off and modified if you want to go after everything you are capable of with the plate.
In general you will need an accurate tachometer and a gps. All testing should be done with the weight as constant as possible and in the same place in your boat. Ya' burn a couple gallons of gas? Put it back in to keep the weight the same!
Run a two way average if in a current or windy condition.
Establish your intial height by making the cavitation plate parallel with the bottom of the boat and measure with a straight edge from the bottom of the boat to the bottom of the cavitation plate to establish that height. From there you can mark your plate in whatever increments you want and note the heights for your performance gains in your log.
If you change running angle of the engine you need to run your height numbers again.....unless you have trim and tilt.
Run a base line. Note speed and RRM at WOT
Would go up an inch to begin with.........run your numbers
Keep going up until your RPM's increase and your speed stays the same or drops. This is the point that your slippage rate has reached and or passed its limit.
Always make sure you have adequate cooling. Various makes and models of engines have water inlets in different places. Some can run higher than others.
Modify your propeller at this point if you want to keep going up.
Have fun!
Lordy - I wish a moderator would make this into a sticky!
 

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