Mercury / tohatsu/mariner 20hp fourstroke
If you have this engine and a light sib (honwave 3.8 or lighter) I have a new 9.25 x 11.5 prop for sale on eBay
I tried it on my honwave 4 and achieved 5500 rpm a fair bit away from the 6100 possible
Top speed reached 22 mph at 5500 with only me on board and a tank of fuel.
The original prop 9.25 x 10 reaches 6000rpm and 25 mph on a good day.
I think that a mercury mini rib or light sib could benefit