johnson 175 1987 jack plate problems

[derekamundsen]

I own a 20ft robalo cc with a 175 johnson 2 stroke 1987.. I have the motor on a power lift (jackplate)... the problem I'm having is when the boat is plained off water is shooting up through the channel that the jackplate provides... when that happens the water also hits the bottom of the motor and comes into the boat very forcefully... the motor has a 25 inch shaft... could the motor be to low to high???? Any help would be great thanks....

 

[emdsapmgr]

Re: johnson 175 1987 jack plate problems

When on plane, the water streaming from under the bottom of the boat should run just under the antiventilation plate on the lower unit. That's the wide flat plate just above the prop. If that plate is buried in the water (engine too low/deep in the water) when on plane, you can get excessive spray and reduced performance and fuel economy. With an electric jack plate, it should be an easy fix.

 

[bob johnson]

Re: johnson 175 1987 jack plate problems

you need to get a plate that is sometimes refered to as a HOLE SHOT plate bolted up to the bottom of the jack plate.


or get any type of sheet aluminum and bolt it to cover the bottom opening of the jack plate...you probably have a large set back jack...i have a 10" setback and I had that issue as well..

bob

 

[SparkieBoat]

Re: johnson 175 1987 jack plate problems

i formed a thick piece of aluminum plate and bolted it to the bottom of my 4" set back jack plate, it helped greatly but did not completely cure the spray, I have a 25" shaft on a jack plate and my boat should be running a 20" shaft. I am about to install trim tabs which should lift the transom a couple of inches to stop the spray and give me better hole shot and stop porposing. you may consider trim tabs also after installing a plate