Anomalous Behavior of Merchant Ship Steering Systems

Abstract

An unusual combination of circumstances occurring during an Atlantic crossing of a highspeed containership created a situation where the rudder, acting in response to automatic steering control demands, caused excessive ship rolling. Further investigation revealed the existence of an unstable condition due to a combination of asymmetrical hydrodynamic and mechanical characteristics and the interrelationship of ship motion and control actuation. Similar response has been noted on other high-speed vessels and is a cause for major concern in future containership operations. The elements involved in creating these conditions have been examined in detail and a plausible explanation has been evolved as to how they can combine to produce the observed results. With an understanding of the causes of this anomalous behavior it is possible to devise means for preventing its occurrence in future designs.