We have a 22 ft pontoon boat with a 115 mercury verado. It has a 21 1/2 inch prop with. 15 pitch. The prop seems to be overreving and the boat is slow. It’s not making much of a wake behind it just seems to be churning the water. There is no rooster tail. An 18 ft pontoon boat with a 50 horse 2 stroke goes way faster than ours. What could be wrong?