I have a new to me Duckworth aluminum welded Navigator 172 (17.5 feet in length, 7'9 1/2" width) with a F90 Yamaha motor with a 13 x 19 SS prop. The tested weight is 2,400 lbs. Using a GPS going out and back I recorded a top speed of 32.6 mph at 6,200 RPM. A Yamaha test bulletin...