Propeller Diameter

A boat propeller is described by its two basic dimensions: diameter and pitch, expressed as diameter x pitch, usually in inches.  Propeller diameter is measured from the circle created by the blades fully open when deployed and under power (not folded or feathered). 

Diameter is the single most critical factor in determining the amount of power that a propeller absorbs from the engine and transmits into the water – the amount of thrust delivered.  The larger the diameter, the greater the efficiency.  A small increase in diameter dramatically increases thrust and torque load on the engine and shaft.  Just like if you have a high powered engine in a car, you need wide tires to get the HP to the asphalt. The reason why dragsters have very wide rear tires.

Large blade surface area (wetted surface) will translate to more thrust.