I have a 14' McKee Tri-Hull that I recently restored. I added a tach for diagnostic purposes and I have found the RPMs to be well below reccomended at WOT. The engine is an '83 Evinrude 70hp. Curently at WOT I am getting around 4900rpms at 29kts with a 13.25x17 MWC prop. THe prop has seen...