A jackplate will let you adjust the height of your motor. Most around 5" of vertical travel. There are many different varieties of JP's. Different setbacks (distance they set the motor back off the transom),different versions of slides,and whether they are manual or hydraulic. The main use for them are for go fast boats that are trying to run their motors as high as possible for less drag,while maintaining prop bite and water pressure to cool there motor. But as I suspected when I built mine on a tritoon we can use them to drop the motor for more trim. Not only that,it will also gain leverage to lift the bow same as a longer pry bar would. I didn't realize that normal was only 1/4 trim. I just knew looking at mine there was no way I could trim it out. I've been running them on different hulls for 20 yrs.
I'm using a hydr. 6" CMC. I'd stay with 6" or less of setback to keep stress to a minimum on the transom. I don't think there's any reason to even try a manual on a pontoon,as when I'm loading or running shallow I raise it to the top. Once away from the dock I bottom it out and leave it there. I mounted mine so the center of adjustment was near the same height as the motor was hanging on the transom. This gave me around 3" of drop,and 2" higher when loading on the trailer.
Now before you hold me to numbers,let me try mine out at only 1/4 trim and center on the plate. Haven't even tried that because it'll launch at 3/4 trim with the plate down. I just know between 3/4 and full trim I'm still gaining speed. We'd have to also see what transom angle your running compared to mine. Side view photos at 1/4 and full trim would help there.
