How does a controllable pitch propeller work?

A controllable pitch propeller (CPP) operates by allowing the angle of the blades to be adjusted while the propeller is in motion. This adjustability enables the vessel to change its thrust efficiently without needing to change the RPM of the engine drastically.

The correct answer highlights that the propeller blades can modify their angle of attack at the hub, which is critical for controlling the thrust generated by the propeller. Additionally, reversing the direction of rotation is an operational feature that allows the vessel to move astern. This capability is particularly advantageous in terms of maneuverability and control, as it allows for rapid directional changes.

In a controllable pitch propeller system, hydraulic systems are often used to change the blade angles in real-time based on the operational needs of the vessel. However, while hydraulic pressure is essential for adjusting the blades, simply changing the hydraulic pressure does not inherently reverse the direction of rotation or address the angle of attack in the broader context.

Overall, the ability to adjust the angle of the blades enhances the vessel's operational efficiency, providing optimal thrust for various maneuvering situations while maintaining control over speed and direction.