Shearwater Porpoising problem

[paublo25]

First off THIS IS NOT MY BOAT, I am just extremely curious as to why this could be happening. A little information on the boat, Shearwater 25LTZ w/ 300 Merc Verado, hydraulic jackplate, trim tabs, power steering and other stuff not needed for this question. Ok this boat is for my father-in-law and ever since he bought it 3-4 years ago it will porpoise out of no where, water can be glass smooth. He adjusts the motor, and starts using the trim tabs after that, he also lifts the motor up. Now this past weekend I paid attention to the motor while we were running and I noticed something odd to me that I don't remember seeing on other boats that I have ran in. Out the hole water will come up between the motor and hull. While we run when front bounces up and while running flat I noticed water spraying up and away from motor, almost like something flat would be dragging right in front of the motor. Then when we stop before the wash gets to the boat the water will spray up and onto the back of the boat and up almost to the top of the motor. Another thing is this boat is really really slow out the hole. With 5-6 people in the boat, 4 by the center console and 2-3 right behind it, we almost have to move people to the front to get the boat on plain faster. I wish I had pictures but didn't have my phone on me at the time. I'm just extremely curious why this is happening and any would like any of the vets input on this matter.