Some ships spend most of their lives in the open ocean where the water is deep in relation to their draught. In such waters these vessels will probably navigate for long periods of time on unchanging courses and seldom come close to each other. At the start and finish of each voyage they pass into shallower and more congested waters in which they may find themselves close to other ships, the seabed or the boundaries of a fairway. In these situations the ship handler is frequently called upon to carry out manoeuvres of a much greater order of difficulty than those attempted in the open sea.

Other types of vessels, by the nature of their duties must of necessity work close to other ships, the obvious examples being tugs, pilot launches and, in MOD(N), ships engaged in replenishment at sea operations.

Yet other vessels move daily along rivers, canals and other waters whose navigable width and depth are for some reason restricted.

All these ships may experience to a greater or lesser degree the hydrodynamic phenomena known as interaction.

The purpose of this paper is to examine some aspects of interaction, illustrated by work carried out at the National Maritime Institute, both to gain a deeper understanding of the phenomenon and to indicate problem areas in the handling of ships in situations where shallow water as it is in such waters that interaction may be most severe and the room to manoeuvre most restricted.