How to measure prop to pad motor height

[Mike Cork]

This was a great illustration posted by a member here on UB. I wanted to take it out of the thread it was in and post it here so we can sticky it.

[Mike Cork]

Just wanted to add that unless you're running and Allison or a Bullet (lots of variables with these and set ups very extremely), a good starting point is 3.5" to 4" inches pad from propshaft distance. This will get you a stable ride and should keep most rigs that are not over powered to a close range of RPM. From here make adjustments in a quarter of an inch until you find your desired performance.

[-Joe-]

I will like to add another tip. As you raise at 1/4" increments, keep an eye on water pressure. Not sure on Rudes and Yammies, but Mercurys needs to keep a minimum of 15-17 PSI of water pressure at WOT. If you can keep PSI and start hitting you rev limiter then you may need to prop up a size or two. I found my best top end at 2 1/4' below pad on my Triton.

[Mike B.]

This is great information, thank you guys for posting.  I had a real problem when I Bought a new ranger in 2014.  The boat did not like The Fury that came on it, ended up putting on a tempest.   This information would have been very helpful as I remember only getting small tidbits of information from different sources at the time I needed it.

[Bud Kennedy]

Here is a link that has a great graphic of the measurement process.

http://www.stevescustomprops.com/faq.html#How_do_I_adjust_the_Prop_shaft_engine_height_

[Mike Cork]

Thanks for the link Bud, I didn't know the original image was lost.

[Bud Kennedy]

Here is the main text.


1.) Level the boat. Place a level under the pad of the boat. Adjust the trailer jack up or down till boat is level
2.) Level the motor. Place the level on the cavitation's plate, and trim the engine down till it's level
3.) Measure from the ground to the pad, Write the measurement down
4.) Measure from the ground to the center of prop shaft, Write it down.
5.) Deduct the two measurements. You want the prop shaft 3 1/2" below the pad of the boat.
6.) Adjust the jack plate up or down, paying close attention the water pressure and max. engine rpms.
7.) On lighter hulls with low water pickups, running at a neutral trim angle is best. To find the neutral trim angle, simple turn the ignition key on when you have set the engine at level. The needle will be pointing to a neutral position. If needed mark the trim gauge for future reference.

Graphic Representation

URL=https://imageshack.com/i/poiUz1m7j][/URL]