Ascertaining the position of a ship by radar

The second paragraph of Article 16 requires that a steam vessel hearing, apparently forward of her beam, the fog signal of a vessel the position of which is not ascertained, shall, so far as the circumstanc­es of the case admit, stop her engines, and then navigate with cau­tion until danger of collision is over. A vessel's position cannot be said to be ascertained under this article, by whatever means, unless it is quite certain that she is the vessel which is sounding the fog sig­nal.

Provided that an echo on the PPI is known to be that of the vessel whose fog signal is heard an efficient radar set is a more rapid and ac­curate means of "ascertaining" that vessel's position than any that can have been in mind when the rule was introduced; but the problem of identifying a particular echo on the PPI with a particular sound signal heard is a difficult one to solve in some conditions and may be impossible in others. Further, if the vessels are at close-quarters, as

envisaged by the rule, and if each has ascertained the other's posi­tion by radar, a dangerous situation may develop should both regard themselves as free of the responsibility for the extreme caution which the rule requires. The radar of the present day is not capable of rapid detection of alterations of course and is therefore unsuited to deal with swiftly developing close-quarter situations.

All that can be said on this question, therefore, is that if a vessel using radar is confident that she has identified the vessel making the fog signal, and therefore chooses to regard herself as free of the limita­tions imposed by the Article, she would be wise still to act with the greatest possible caution.

Radar and the steering rules

(Articles 17—27)

The main question today in the mind of the master of a vessel which detects another ship by radar on any bearing and at any dis­tance, but cannot see her, is likely to be whether he is free to alter course or speed as he thinks fit or is in a situation to which the Steer­ing Rules apply.

On reading these rules it is impossible to avoid the conclusion that they were written for vessels in sight of one another. For one thing, the rules vary according to the type of vessel encountered, which can be determined only by the eye; for another, they imply that apprecia­tion of the situation by the two vessels concerned is mutual; for exam­ple, the effectiveness of the action prescribed by Article 19 depends on the other vessel's taking the action prescribed by Article 21, and vice-versa. This mutual appreciation may safely be assumed when one vessel sights another but not when radar is the only means by which she detects the other.

The Steering Rules form an arrangement for mutual safety brought into effect at a time obvious to both parties. In good visibility this should be a perfectly straightforward and commonsense affair and, even if there should be some local difference of opinion as to the distance apart at which ships should consider themselves bound to the course of action ordered, there is unlikely to be any such difference in law. When, owing to low visibility, ships which have no radar are out of sight of one another and are also outside sound range, none of these considerations can apply and there is no rule to govern their movements other than that which requires speed to be moderate.

All the foregoing arguments are based on the Steering Rules as they have been applied and are still applied in the absence of radar. The question now is whether the advent of radar has created a new situation. It must be considered from the point of view of own ship only having radar since the legality of any action she may take can only be based on known fact or reasonable assumption, and the effec-

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live use of radar by the other ship will not come under either of the classifications in the foreseeable future.

The idea of two ships being bound by an arrangement for mu­tual safety, operative at a time obvious to both, though quite reason­able in the visual case, falls to the ground when radar is the only source of information. There can be no mutual understanding about a meeting in such circumstances and therefore no assurance that the other vessel will take any particular action. Without that assurance no rule mutual conduct can carry any guarantee of safety.

There seems to be an impression in some quarters that the cors-sing rule (Article 19) has an implication that a vessel approaching unseen in low visibility from the starboard bow constitutes a greater danger than one coming in from another point. Should it happen that the other vessel is not using radar and is, therefore, unaware of the posi­tion of own ship, she will, other things being equal, have no reason to alter her course and speed but will continue her approach unless and until Article 16, Par. 2, becomes operative. Whatever bearing she happens to be on will, if it is steady, be a dangerous one. An argument that the other vessel may be employing radar cannot alter this fact because, even if every ship carried radar and could be assumed to be operating it competently, there would be no possibility of ascertain­ing in the general case the use to which the radar information would be put. Own ship would be well advised to take this unknown quan­tity into account in every case.

It will be appropriate here to mention the subject of radar blind sectors. Whatever the limits and directions of such sectors, they may possibly conceal an approaching vessel and the responsibility for keep­ing a good lookout is clearly defined in the rules (Article 29). When circumstances require it, the master will no doubt decide how often to swing the ship a few degrees to open up the blind sectors, or whether to snake the course of the ship regularly. The method employed will probably depend on the size of the sectors and their position. The lat­ter factor is not a question of some bearings being more dangerous than others, but merely that the relatively slow rate of approach of a vessel from after bearings may permit a somewhat less frequent, though still faithful, observation of them.