"Jere Lull" wrote

My personal opinion, remembering that I travel at less than hull speed, is
to fit the largest diameter prop possible, then find the pitch that just
allows you to max out in normal conditions.

Generally good advice but, if any kids are going to try this at home, they
should be aware that "largest diameter possible" means with an absolute
minimum tip clearance of 10% of the diameter. That will still be noisy,
the thump of the tip vortex hitting the hull each time a blade passes would
be pretty annoying in a powerboat but perhaps tolerable in a seldom run
auxilliary. If you want a smoother installation, try to get closer to 15%.
20% is not uncommon in powerboats where smooth running is important.

--
Roger Long