When do you know the motor is set up and trim right?

I was out checking my boat after water pump install and have a question on trimming the motor. I have 3-5/8" prop to pad, 23 tempest Plus on an 150 Mercury w/5.5" JP, it reach 50 mph (GPS) at 5600. (48 MPH at 5400 RPM is about were I run it). Rooster tail a little above motor. I was playing around with the trim, and kept trimming it up and could tell it was getting on pad more and RPM was picking up, but water pressure was dropping. Are there a correct angle for the motor to be trim at?

It's a 87 ProCraft 1780V. I was told at a dealer that the boats were built to run with the Anti-ventilation plate level with the bottom of the boat at that, the motor would be around 5" below the pad.
I google this and been reading about boat set up, not sure what is correct, does the old boats set up different them the new boats?

A few years ago I had this boat at 3-1/4 PTP, at 6000 RPM, 55 MPH. (at 5800 RPM and 52 MPH the boat was easy to drive, cable steering). The motor was taken off and a part of the transom was repair, I think the jack plate was installed on different mounting holes, But isn't the prop to pad height measure the same regardless of mounting?


Thanks
Rick

Not every boat will have the exact same prop to pad measurement, it’s just a starting point. If you have a jackplate, you adjust it in 1/4” movements and then take her out for a test drive. When your water pressure drops below the min pressure recommend by the motor company, then you know that you’re too high, so drop her back down a little bit. If your steering starts to get really stiff, then your too high.

and yes it’s possible to have too much trim, some boats require maximum trim and some take half trim.

You want to find out where it belongs?
You'll need to spend some time to find too much. What is too high and what is too low, is the only way you'll know what's just right.

"Just Right"
Full Power Full Trim. You'll have prop torque wanting to pull you right. Normal.
Roostertail no higher than motor cowling.
Boat should feel light and a little loose. Stuck to the water is slow.

If you can't do that, exactly like that, then you need to find the place it will.