The application of a multivariable control philosophy to reduce rudder induced warship roll motion

To be operationally effective a modern warship must be able to execute high speed manoeuvres whilst maintaining its fighting capability. This specification of high manoeuvrability has restricted the basic hull design of warships and results in the relatively large control surfaces i.e. rudder and stabilising fins. This often results in severe interaction or cross-coupling between the control surfaces and the controlled outputs. For example, changes in rudder position not only result in desired changes in yaw but also induce rolling motion and because of increased drag, speed reduction also occurs. The execution of high speed manoeuvres therefore can inflict severe restrictions on a number of warship tasks that are adversely affected by yaw. The successful application of the direct Nyquist array methodology for the multivariable analysis of warship manoeuvring is described. The aim is to improve warship manoeuvring characteristics by reducing undesirable cross-coupling effects