When the trailing edge of an outboard propeller blade is formed or cast with a curve that rolls away from the boat it is said to be cupped. Generally cupped blades improve a boats ability to break plane. Cupping helps the prop to "bite" the water better and hold or not break loose when operating in a cavitating or ventilating situation. Cupping can improve hole shot, reduce slipping and allow for quicker acceleration. It also can permit the engine to be trimmed out further or be mounted higher on the transom ultimately adding to your top end speed.
Cupping essentially has the effect of adding pitch and rake to the propeller depending on its placement along the trailing edge. According to Quicksilver Propellers, it can also reduce WOT (wide-open throttle) engine speed by roughly 150-300 RPM below the same prop with no cup. The propeller technicians at Bobby Soles Propeller can increase or decrease cup to alter engine RPM to meet specific operating requirements. Cupping is typically standard in today's OEM and after-market propeller designs.
Check us out at bobbysolespropeller.com or call today 561.848.6678