Diffrac calculations on the manoeuvring co-efficients of a barge unit

On behalf of Rijkswaterstaat computations were carried out at the Netherlands Ship Model Basin. The objective of the calculations was to arrive at an estimate for the manoeuvring coefficients of a barge unit consisting of 2 barges in tandem pushed by a tug. Points of investigation were the effects of shallow water, the effectts of a channel of limited width and the effects of adduracy of the mathematical description of the problem. The calculations were performed with the N.S.M.B. wave diffraction program DIFFRAC. On basis of calculations for deep water and a comparison with strip theory results it was concluded that a detailed mathematical description of the barge unit is required in order to improve the accuracy of the calculations. The results of calculations on unlimited shallow water show that "end effects" are of importance. The effects of a channel proved to be limited for the case under consideration.