Cruise Ship Propeller

A: The cruise propeller has a higher pitch, therefore more drag. More drag results in lower RPM and less horsepower capability, which decreases performance during takeoffs and climbs, but increases efficiency during cruising flight.

A: While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting of an electric motor or internal combustion engine driving a propeller, or less frequently, in pump-jets, an impeller.

A: In cruise flight, increasing the angle-of-attack of the prop also increases the engine's torque. This increase in torque effectively slows down the engine, resulting in improved fuel efficiency.

A: Because the engines are usually turning a crankshaft at a very high rate of speed (often hundreds or thousands of revolutions per minute), the engine is connected to the propellers through gears. Propellers are designed to turn much more slowly -- usually 250 revolutions per minute or less.

A: The back side of the ship is less likely to sustain damage from foreign objects than other parts of the ship. The propeller's location allows water to flow over the ship's rudder, which improves manoeuvrability and control, especially at low speeds.

A: All propellers are statically balanced when manufactured or properly repaired. Dynamic balancing uses a special machine to rotate the propeller and measure the amount of imbalance. In general, dynamic balancing insures the amount of imbalance is kept to a minimum or within a specified tolerance. It does not guarantee a propeller will perform without vibration though since there are a number of factors not relating to propeller balance that may cause vibration. Also, providing the static balance equipment is of good quality and properly maintained, statically balanced propellers will usually be just fine.