Hydrodynamic Interaction between ships on opposite course in a narrow channel:
- On close approach, the combined positive bow pressure zones encourage the respective bows to be repelled and, if speed is excessive, may require vigorous corrective helm.
- When abeam, the combined low pressure zones encourage a suction which, if the vessel’s are very close, can cause a violent broadside collision. The bow of each vessel now comes under the influence of the other vessel’s stern, which also means the rudder of each vessel is being affected by the positive pressure of the other vessel’s bow. This causes each vessel to take a sheer towards the other vessel and, if in a narrow channel or fairway, for the stern to be cast towards the boundaries of that channel of fairway.
- As each vessel draws clear the combined low pressure zones cause the sterns to be drawn towards each other and assist the vessels to regain their original track.