The 1972 IMCO (Inter-Governmental Maritime Consultative Organization) Rules came into operation two years ago on July 15, 1977. Compared with the 1960 Rules, which they replaced, there were many changes in both format and wording and also some important changes in principle. The intention of the IMCO Committee in changing the format and wording was to make the rules more easily assimilated and understood but inevitably there are problems as to how some of the new phrases should be interpreted. In the long term, it will be possible to base interpretations on court rulings but it will take many years for the case law necessary for this purpose to accumulate. In the meantime, mariners have to make decisions based on their own interpretations, and disputes which do not come to court have to be decided on interpretations agreed among the parties.

Many general discussions of the changes in the collision regulations have been published and it is not proposed to repeat this exercise yet again. The present article will instead examine one of the areas where the rules may be defective.

Most collisions in the past have resulted from situations in which the ships involved were initially meeting on nearly opposite courses and such that, if both had maintained their original headings, a close starboard to starboard passing would have occurred. In encounters of this type, one ship might consider that risk of collision (or, in fog, risk of a close quarters situation) existed, and would therefore alter course to starboard in accordance with r. 14 (or, in fog, r. 19). The other ship might consider that a safe passing existed with no risk of collision (or, in fog, no close quarters situation) and thus feel justified in turning to port in order to gain more sea room. This combination of actions is a classic recipe for disaster and it is probably a defect in the rules that such conflicting interpretations can be quite legitimately arrived at by two parties viewing a common situation.

One of the problems seems to be that, while mariners are generally comfortable with an alteration of course to starboard, they do not like doing so if it takes them across the bows of an approaching ship. Certainly if the tracks of two ships meeting one another are separated by say a mile, it takes strong nerves on the part of the master of the slower ship to alter course to starboard with the knowledge that he has to give up a close but safe starboard to starboard passing situation and put himself at some stage across the path of the approaching ship before he begins to build up a clearance on the other side. In experimental work under simulated fog conditions, experienced mariners were found to divide so that almost exactly 50% chose a starboard alteration of course and 50% chose a port alteration of course under such circumstances. Clearly this almost random choice of action is undesirable but it is not so clear as to how the applicable rules should be changed so that more predictable and better co-ordinated manoeuvres are made. In order to investigate this matter it is useful to look briefly at the history of the collision regulations.

From 1840 to 1863 the rule for steamships meeting was that, whatever the relative courses, collision was to be avoided by each ship altering course to starboard. This proved to be a disastrous rule, not because it failed to resolve the situation when ships