What is the advantage to a cupped prop?
A cupped prop can be run higher to the surface, as it holds the water better and slips less than an uncupped version. A cupped prop is going to run less RPM when wide open as it is pushing more water. It is like running a higher pitched prop. If a boat is running a 21 inch uncupped prop, a 19 inch cupped prop will usually turn about the same RPM, but will have better power out of the hole, and might even run a little faster as the engine or drive can probably be trimmed up higher.
