STEERING AND SAILING BULBS 213
If it had been 6 points on the bow, the point of collision would have
been 2£ miles away, and have been reached in 15 minutes. This is
illustrated in the annexed diagram.
Ay B, and C are vessels 1 point, 4 points, and 6 points on the bow
respectively. Aly B^ and C^ the respective points of collision with Z),
assuming each one to be going at the same speed as Z>.
Of course at sea you never know the speed of the other vessel, but
the foregoing is useful, and points out that when it is your duty to keep
out of the way of another vessel the more nearly she is ahead of you the
greater is the need for prompt action. Also, when a light bears nearly
ahead, and it is your duty to "keep out," it is hardly necessary to wait
to see if the bearing alters, as a slight change of your course in the right
direction will convert the position into one of safety.
So far no notice has been taken of the lengths of vessels. This is air
important factor, and one which must be considered. Its importance
rapidly increases as vessels near each other. In order to avoid collision,
the whole length of one vessel must pass clear of the crossing point
before the stem of the other reaches it; therefore, not only must the
^bearing change but it must change appreciably, otherwise risk of collision
must be deemed to exist. You must use your own judgment as to what
constitutes an appreciable change of bearing.
Notice also the words^ "when circumstances permit," as cases may
arise where it may be advisable and necessary for the giving-way vessel
to act immediately and not to wait to see if the bearing alters.
Avoiding Collision.—Articles 21, 22 and 23 deal more particularly
with the avoidance of collision. Article 22, and also common sense,
require that the vessel which has to keep out of the way shall, if circum-
stances permit, avoid crossing ahead of the other—the latter being
required (by Article 21) to keep her course and speed except in special
cases. (See Note, Art. 21.)
Refer to Figure 3 which is intended to represent four ships on con-
verging courses and heading for a common collision point. Assume
yourself to be in ships A, B, C and D in turn with only one of the .
other three vessels in sight, that is, cover any two of the vessels with
your hand and state what you would do if there was risk of collision
with the third vessel, assuming there is room to manoeuvre.
In Ship A.— (1) Keep clear of B (Art. 19). I would alter course
to starboard and go under his stern, or, if very
close I would slow down or stop and let him