Page 70 - Collision Avoidance Rules Guide

Alterations of speed take longer to put into effect than alterations of
course so they are less likely to be readily observed. If a reduction of
speed is to be made the way should be taken off as rapidly as pos-
sible by stopping the engines. Slow ahead or dead slow ahead can be
ordered subsequently.
When vessels are in sight of one another it will probably be
sufficient to make alterations of course which will be readily appar-
ent to a person observing visually from the other ship. The Rule
refers to 'another vessel observing visually OR by radar'. Alterations
of course of less than 10" are unlikely to be accepted as satisfying
this requirement. A giving-way ship which alters course to pass
astern of the other vessel should preferably turn sufficiently to bring
the other vessel on to the opposite bow, so that at night a different
sidelight would be visible, then gradually turn back maintaining the
same relative bearing, until the original course is resumed.

A common factor of many collisions involving vessels using radar
has been the number of small alterations made by one, or both, of the
vessels concerned. Small alterations are unlikely to be detected by
the other vessel and may increase the danger of collision. In the case
of the British Aviator-Crystal Jewel 1964 (referred to on page 47)
the British Aviator failed to appreciate the series of small course
alterations made by the Crystal Jewel, and considered that as the
bearing was changing there was no risk of collision.
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