BARGE MOTIONS AND TOWLINE TENSIONS MEASURED DURING A NORTH SEA TOW

During the tow, in March 1978, of the ocean-going deck cargo barge Jasmine's Turtle from Newcastle-upon-Tyne to Stord in Norway, measurements were made of the vessel's motions and towline tensions. The purpose was to investigate the dynamic response of the barge in a random sea and calibrate methods of calculating barge motion response. This paper concentrates on the analysis of the towline tension data. The tension time-histories showed large amplitude fluctuations such that, under certain conditions, the towing tension could attain peak values of twice the mean static tension. The tension data was correlated with measured barge motions, and at low speeds (less thn 1 knot) a reasonable agreement was found. At normal speeds, however, the tension spectra remained uncorrelated with any of the measured motions. It was inferred that this was due to the dynamic response of the barge-cable-tug system. A simple analytical model was developed, which provided reasonable correlation with the measured response. This model also serves to illustrate the range of conditions under which dynamic problems may be encountered. Order from BSRA as No. 54,664.