With the development of the shipbuilding industry, the scale of ships has increased, and towing operations have gradually expanded to shallow water. The hydrodynamic characteristics of a ship traveling in shallow water are very different from those in deep water. Methods derived from open water are no longer applicable in shallow water. Performance analysis of shallow water towing system is needed. The towing performance in shallow water is of great importance to the smooth operation of towing.
The calculation of cable tension based on potential flow method cannot reflect the influence of shallow water drag increase phenomenon on cable tension. Therefore, the frictional resistance line of the KCS boat in shallow water was corrected. Then the resistance extrapolation is performed to obtain the fluid load. Catenary model is introduced to simulate cable model, and six DOF motion of rigid body model for the motions of the ship. Numerical simulations of the forces on the towing system at different water depths were carried out. The effect of shallow water conditions on towline tension was studied and investigated. The results show that the increase in tension caused by shallow water can range from 10% to 30%. There is a certain guidance for the cable selection in shallow waters and the power selection for towing vessels.
When the towing system sails from the deep water area to the shallow water area such as ports, inland rivers, and shallow seas, the distance between the bottom of the ship and the bottom of the water constitutes shallow water conditions, which in turn affects its hydrodynamic performance. The shallow water effect can be studied by experimental methods and CFD (Computational Fluid Dynamics) methods. Simonsen(2006) did a complete set of VLCC2 shallow-water experiments, and obtained the VLCC2 resistance curve under different water depth and drift angle. Mucha(2017) conducted a model test of inland river boats to calculate the shallow water resistance of inland river vessels.
