ABSTRACT:

In order to ensure the safety of towing operation, it is important to understand the motion characteristics of a towed ship and the tension behavior during towing in waves. In this study, a time domain simulation method for the wave-induced motions of a towed ship and the towline tension in head seas is presented. The predicted results were compared with the model test results. The results in time domain quantitatively agreed with the test results. The present method is useful for predicting the wave-induced motions of a towed ship and the towline tension during towing in waves.

INTRODUCTION

Towing operation is widely carried out to transport an uncontrollable ship such as barges and capsized ships. In most cases, slewing motion of a towed ship occurs during towing. Therefore, maneuvering motions of tow and towed ships and course stability of ship towing system in horizontal (X-Y) plane have been studied by many researchers. However, the towing operation is often done in waves. In order to ensure the safety of that operation in waves, it is important to understand the surge, heave and pitch motions of tow and towed ships and the tension behavior in vertical (X-Z) plane. Fang proposed a simulation method of ship towing system in random waves which included both the horizontal and vertical motions of ships. But, his calculated results were not compared with experimental results and so the accuracy of the calculation method was still unclear. When the motions of tow and towed ships are formulated, a problem to be carefully considered is how to express the tension acting on the towing point. Kijima (1983) estimated the tension using a resistance coefficient of a towed ship in still water and Yukawa (2002) estimated the tension using catenary model equations.

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