Buddy has a 18' pontoon, 35hp motor. moves same as it did with a 25hp 30 years ago. all of 14-15mph.... on a 7 mile long lake, would take 30 minutes to get to the other end.
you may want to check your math there. to do 7 miles in 1.5 hrs is needing to be running 4.67mph to do it in 1 hour...