Numerical Simulation of Ship Maneuverability in Wind and Current, With Escort Tugs

Abstract

A number of recent large-ship accidents have compelled naval architects and engineers to advance the research on ship maneuverability and the prediction of ship response in the ocean environment. In the meantime, new maneuverability standards have been developed and the International Maritime Organization (IMO) has also proposed one such standard. This standard provides four ship-maneuvering performance criteria, and its latest version is dated December 2002. Simulation technology, in particular the simulation of ship maneuvering, has advanced considerably in recent years with the advent of computers. Computer programs using either numerically computed or experimentally determined hydrodynamics coefficients have allowed an accurate simulation of ship maneuverability for different types of vessels. Relatively good agreement has been reported by various researchers between simulated results and those obtained from full-scale ship trials. It seems that simulation can now identify acceptable ship maneuvering performance in calm seas. However, the effects of wind and current and escort tug assistance have not been that well studied and reported, and they are always important factors for ship maneuvering especially in restricted waters. The numerical simulation program presented in this paper (UBCManeuver) has been validated using data on the Esso Osaka 278,000 DWT tanker, a ship well tested for regular maneuvering tests. UBCManeuver is able to identify IMO class and non-IMO class ships according to the most recent IMO standards for ship maneuverability. A good agreement was obtained between simulation and the sea trials reported for Esso Osaka. After the validation of the code, the course-keeping abilities of this ship in restricted waters were studied in calm seas and under wind and current conditions. The effect of escort tugs on such an operation has also been quantified and Esso Osaka's maneuvering performance around Vancouver harbor simulated. The limits of current and wind strengths for "successful" operation with and without escort tugs have then been established. In addition, the effectiveness of multiple tug assistance in different positions is discussed in some detail.