Exam Question
(a) List the various types of screw propellers used for ship's propulsion. (5)
(b) What are the advantages and disadvantages of CPP. (5)
(c) With a simple sketch of a fixed pitch propeller explain Rake, Leading and Trailing edge (6)
Class 4 (4th Engineer)
SC&S
📅 Jan 2023
Reference Answer
### (a) Types of Screw Propellers
Based on design and operational principles, marine screw propellers can be classified as follows:
1. **Fixed Pitch Propeller (FPP)**: This is the most common and robust type. The blades are cast or forged as an integral part of the hub, meaning their pitch is permanent and cannot be altered during operation. FPPs are designed for maximum efficiency at a specific design speed and load condition. They are mechanically simple, reliable, and cost-effective.
2. **Controllable Pitch Propeller (CPP)**: In this design, the propeller blades are attached to the hub via a mechanism that allows their pitch to be changed hydraulically. This enables the engine to operate at its optimal RPM across a wide range of vessel speeds and loads, improving fuel efficiency and maneuverability. Reversing is achieved by changing the blade pitch to a negative angle, eliminating the need for a reversing gearbox or a reversible main engine.
Based on design and operational principles, marine screw propellers can be classified as follows:
1. **Fixed Pitch Propeller (FPP)**: This is the most common and robust type. The blades are cast or forged as an integral part of the hub, meaning their pitch is permanent and cannot be altered during operation. FPPs are designed for maximum efficiency at a specific design speed and load condition. They are mechanically simple, reliable, and cost-effective.
2. **Controllable Pitch Propeller (CPP)**: In this design, the propeller blades are attached to the hub via a mechanism that allows their pitch to be changed hydraulically. This enables the engine to operate at its optimal RPM across a wide range of vessel speeds and loads, improving fuel efficiency and maneuverability. Reversing is achieved by changing the blade pitch to a negative angle, eliminating the need for a reversing gearbox or a reversible main engine.
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