Another title could have been Boat propeller Diameter on command trust or big foot motors.
Many factor will influence rpm and diameter is one of them. I am seeing in the last several seasons some large pontoons being pushed by 60 hp engines that are command trust /or Bigfoot. This means that the gear case is in a larger category
The problem is that the lowest pitch props available for a bigfoot 60 hp would be 14×11 and reaching the minimum recommend RPM range becomes impossible….Same engine with a non-command thrust or not a big foot can runs a 2” smaller diameter propeller and a lower pitch is available
the key is the fact that it is also 2 “ shorter in diameter
In this case the lowest pitch available becomes a 12×9 an increase of about 900RPM
At Canada Propeller our tech support team will be happy to answer any questions relating to propeller selection