Assumptions about the other ship

The possession of radar by the "other" ship is one of the unknowns which frequently enter into discussions on the use of radar. It is rea­sonable to assume in clear weather that, following the Steering and Sailing Rules, the man on the other ship's bridge has the use of a good pair of eyes and a working knowledge of the Rule of the Road.

When ships are out of sight of one another, comparable assump­tions would be that the other ship is or is not using radar, but either of these alone would be a dangerous basis for action. The first would involve further assumptions as to the efficiency of the set, compe­tence of operation, intelligent use of the information and some agreed interpretation of the Steering Rules. The second, the assumption that she has no radar, would invite unpreparedness for manoeuvring action by her.

The only safe course is to allow for both eventualities and action, if taken, should be safe whether the other vessel maintains her course and speed or alters them. In any case unremitting observation will be necessary.

OCCASIONS FOR USE IN OPEN WATERS Low Visibility

At least one collision might have been averted if a radar-fitted ship had had this aid in use before she entered a fog bank.

In one case on record a fog bank was sighted 6³/₄ miles ahead in daylight and the other vessel was struck ¹/_a mile inside it.

A proper caution will suggest having the radar set at "stand-by" when there are indications of reducing visibility and commencing to operate in plenty of time to assist in retaining control of the situa­tion. No doubt th^Te will be many occasions on which the warning of fog will be much less than in the example given and it must be admitted that a vessel which enters thick fog at speed without pre­viously sounding fog-signals is likely to be held to have contravened Articles 15 and 16 of the Collision Regulation. When any geographical or meteorological considerations suggest the likelihood of fog, readi­ness of radar for immediate use will no doubt be regarded as one of those precautions mentioned in Article 29.

A collision between a vessel which was skirting a fog bank and one which came out of it is on record. In this case also there was held to be a contravention of Article 15, but the value of the use of radar by either or both ships in such circumstances will be obvious. There are two distinct conclusions to be drawn. One is that it would be most unwise to cruise near to a fog bank without using any available means of knowing what may be coming out of it. The other is that, when using radar in fog, it cannot be assumed that all vessels whose echoes are on the PPI are also in fog and acting with corresponding caution.

Good Visibility

Before leaving the consideration of collision risks in open waters, mention should be made of the possible value of using radar in clear weather. In areas of high traffic density and particularly those in which shipping routes from various directions converge, radar may be of great value in augmenting the information obtainable by eye. When danger is to be apprehended from more than one ship, a radar plot which will give the ranges and speeds of approach of other ves­sels may be of great assistance in resolving the relative urgencies of the situation.