The time intervals shown assume A's speed as 10 Knots, but can be easily

MANOEUVRING TO AVOID COLLISION.

Showing the points at which A and B will meet for various relative speeds.

fulness. If the rudder is to be put to right, this should be done while the ships are separated by a perfectly safe distance, and the course changed to starboard sufficiently to make sure of shutting out the green light from the view of the other ship. It is of course impossible to do this in a narrow channel, nor will it be important to do it there, as each vessel will know the course that the other must be steering; but the change of course should always be made as early as the channel permits.

When meeting another vessel in a narrow channel, there is danger in changing course too much, as to do so opens the broadside to a possible blow from the other ship. A small change made promptly, is safer than a greater change made after the ships are close aboard. On the other hand, there is the danger already pointed out, that, at night, a small change of course will not be seen by the other ship. In this situation, range-lights are especially valuable, as giving instant notice of the slightest change in the heading of a vessel seen end-on or nearly so.

In navigating crowded channels, pilots try to avoid changing course; preferring, whenever it can be done with safety, to keep clear of other vessels by reducing or increasing speed. This is less confusing than changes of course where several vessels are trying to keep clear of each other.

§ III.

STEAMERS CROSSING.

Note. In this section, the steamer having the other on her own starboard hand is called ; the other B.

As preliminary to a detailed discussion of cases arising under this heading, attention is directed to the figures of Plates 129 and 130, in which the vessels are assumed to be separated by one mile, and the courses plotted which в must be steering, for various rates of speed, in order that there shall be danger of a bow-to-bow collision with A.2 2

We do not attempt here to draw any conclusions which involve a knowledge on the part of either vessel, of the course or speed of the other.

It is apparent from these figures that, if there is to be a collision, the point at which it will take place depends upon the relative speed of the two ships. If the speeds are equal, it will be

1 Helm to port.

2 We cannot, of course, disregard the length of the ships; but as a basis of argument we deal here with the bows only. The figures will make it clear in what way the argument must be modified to include the meeting of the bow of one ship with the stern of the other.

at P, equidistant from A and B. If в has the greater speed, the point of meeting is crowded back towards A, and the space available for a to manœuvre is reduced. If, on the other hand, B's speed is less than A's, the point of intersection recedes, and the space at A's command is correspondingly increased. It follows from this that if A is running at a low speed and finds another vessel closing in on her without change of bearing, she will know that the space at her command for manoeuvring is comparatively limited, as, in all probability, the point of intersection of the courses is not far ahead.

As regards B, if it happens that she is running at very high speed, she, too, will know that in all probability the courses intersect near A and that a has probably but little space for clearing her (B's) line. It may therefore be urged that, so far as в is concerned, the obligation upon her to act for the avoidance of collision, under Art. 21 of the Rules of the Road, will increase with her speed; that is to say, if her speed is so high that A's is not likely to equal it, she will know that her course is probably crossing A's at a point which leaves A but little space in which to manœuvre for mutual safety.

As regards the time available in the cases illustrated in Plates 129 and 130, we cannot discuss this without assuming a definite speed for A. In the figures, this is taken at 10 knots, so that B's speed becomes, for the courses laid down, 10, 15, 20 and 7 knots.

If A's speed is greater or less than 10 knots, the intervals must be changed correspondingly.

If we take the distance between the ships as greater or less than one mile, the scale of the figures must be changed.

With these speeds, we see that, when в is distant one mile and crossing without change of bearing, the bows of the two ships will meet after the intervals shown in the figures.

An important point brought out by the figures is that, if B's speed is materially less than a's, there are only certain bearings on which в can threaten collision. Suppose, for example, that B's speed is two-thirds of a's, and that she bears four points on A's bow. She cannot by any possibility reach the line of A's course in time to intercept and collide with her. As the difference in speed increases, this point comes out more and more strikingly. If A's speed is three times B's, there can be no collision if в is sighted more than 134 points on the bow.

It follows from this, that in the case of a steamer running at a speed so high that no vessel which is likely to cross her course can be expected to have anything like an equal speed, the danger sector is confined to a few points on either bow.

Take the case of an ocean liner, running at a speed of 20 knots, and consider her relation, for example, to sailing-vessels crossing her route. These vessels will not have more than one-third to one-half her speed. To threaten collision, then, they must bear a very little on the bow, and can be cleared, in most cases, with a few spokes of the wheel. Although this point is not usually specifically brought out, it is probably somewhat vaguely held as the basis of the contention so strongly insisted upon by the officers of the great liners, that it is safer for them to run at full speed in a fog than to slow down. This subject will be discussed in a later section, in connection with " Fog," and it will be shown that this is only one of many points to be considered in thick weather, and that the unquestionable advantage of high speed from this point of view is much more than counterbalanced by other considerations.

§ IV.

A large proportion of steamers meeting at sea approach each other on bearings from ahead to four points on the bow. It happens that this is, for reasons which will appear hereafter, the most dangerous bearing on which they can approach; and it results from this coincidence of the maximum frequency of occurrence with the maximum of danger, that something like seventyfive per cent of all collisions reported, are between vessels approaching each other on these bearings.

It will be convenient to distinguish two general classes of situations: Ist, Those arising under ordinary conditions, where vessels sight each other at normal distances and have plenty of time and space for manoeuvring to avoid collision; and 2nd, Those in which they do not see each other until dangerously close. If any doubt exists as to whether they are dangerously close or not, it should of course be assumed that they are.

Ist. Masthead lights are required by law to be visible five miles, on a clear, dark night; and this law is fairly well complied with. We shall certainly not be in error if we assume that they will show four miles, and that the side-lights of a steamer will show half as far. If bearings are taken from the time the mast