Purpose of a jack plate?

I see a lot of projects that people have used a jack plate and I wanted to know the purpose of one.

I made mine to use a long shaft motor on a 15" transom.

Well my transom is about 16" in height with a motor that the shaft is about 17". Does anyone think it is worth installing a jack plate to raise the motor one inch?

bhumbertson said:

Well my transom is about 16" in height with a motor that the shaft is about 17". Does anyone think it is worth installing a jack plate to raise the motor one inch?

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You want your cavitation plate on an prop outboard to be about 1 inch below the bottom of the boat when the motor is in the operating position. The greater this measurement the more drag your motor produces in the water. So check that measurement first.

If you're pretty close to 1 inch. Put your boat in the water a see what she does. A jackplate can help you tweak it and get a little more out of your outboard.

Thank you. I'll have to put it in the water and see.

bhumbertson said:

Well my transom is about 16" in height with a motor that the shaft is about 17". Does anyone think it is worth installing a jack plate to raise the motor one inch?

Click to expand...

If that is all the difference you can raise your motor and put a 3/4 spacer under it. I was told to do this once and I used a piece of wood and it improved performance a lot

sawmill said:

bhumbertson said:

Well my transom is about 16" in height with a motor that the shaft is about 17". Does anyone think it is worth installing a jack plate to raise the motor one inch?

Click to expand...

If that is all the difference you can raise your motor and put a 3/4 spacer under it. I was told to do this once and I used a piece of wood and it improved performance a lot

Click to expand...

That's a great idea. Thanks I'll have to try that.

Along with raising the motor jack plates have some setback which lets you raise the motor even more.

You can also raise the motor up even higher if you use a anticavitation plate and a cupped prop. I'm new here , but not new to running boats in flats. The less lower unit you have down in the water the faster and shallower you can run. The downside to this is when backing you aren't getting the full flow from the prop pushing you back . I highly recomend water pressure gauges on all motors. They tell you when you need to replace the water impeller and when your not getting a good flow of water for cooling.