Class 1 (Chief Engineer) Engineering Management 📅 Oct 2024

Exam Question

(a) Discuss what you understand by directional stability and manoeuvring. How are these attributes provided in a ship? (8)

(b) Using typical engine power versus engine speed diagram and propeller demand curves, discuss the relation between the maximum rated output of the propulsion plant and the power for which the propeller is designed (8)

Reference Answer

### (a) Directional Stability and Manoeuvring
#### 1. Concept of Directional Stability
Directional Stability refers to a ship's inherent ability to maintain a straight course without rudder action, or to return to its original straight-line path after being disturbed by an external force (e.g., wind, waves). A ship is considered directionally stable if, upon a deviation from its set course, it naturally tends to correct itself and return to the original heading. This recovery can be either a direct, non-oscillatory return or an oscillatory (yawing) motion that gradually dampens out.
* **Stable Ship:** Will maintain its course with minimal rudder input. It is analogous to a weathercock, always wanting to point into the relative wind/water flow. This makes it efficient for long sea passages (course-keeping).

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