Course Stability and Controllability

In this chapter, the stability of a systemCourse stability and of a ship are briefly considered before examining the stability of the motion of a ship moving at constant speed in a straight line at the surface of undisturbed water. It is shown that a ship is stable in surgeSurge. Three types of stability concerned with direction are considered—straight line stabilityStraight line stability (controls fixed stabilityControls fixed stability), directional stabilityDirectional stability and path stabilityPath stability. The linear equations of motionEquations of motion are used to derive the condition for straight line stability and a physical interpretation of this condition is given. There is a brief description of ship manoeuvres to determine directional stability, a more detailed description being deferred to a later chapter. The chapter concludes with a consideration of controllabilityControllability, defined as the ability of a ship to start and stop changes in direction of motion quickly.