Page 65 - Collision Avoidance Rules Guide

5 miles, fine on the port bow, because the radar bearing seemed to be
opening and the two vessels were expected to pass closely, port to
port. The visibility was excellent and the navigation lights of the Toni
had been seen at a considerable distance but no visual compass bear-
ings were taken. The Judge concluded that the master of the Toni was
keeping a poor look-out and that the Toni had altered course to port.
It seems probable that the two vessels would have passed starboard
to starboard if they had both kept their course and speed and that the
Toni turned to port to increase the passing distance. Both vessels
were found equally to blame.

No appreciable change of compass bearing
Risk of collision shall be deemed to exist if the compass bearing of
an approaching vessel is not appreciably changing, not the relative
bearing, The relative bearing will be affected by changes of heading.
Sighting an approaching vessel against components of the ship's
structure may give a rough indication of whether there is risk of
collision and may provide sufficient basis for deciding whether to
make a bold alteration to pass astern of a vessel being overtaken or
crossing from the starboard side. Such bearings, however, must
always be related to the ship's heading and may be affected by slight
changes in the observer's position unless careful transits are taken.

Risk associated with changing bearing

When two vessels pass close to one another without any changes of
course and speed the bearing which subtends from the other will
remain almost constant at long range and change rapidly at short
range (see table on page 228). An appreciable change of bearing at
short range may therefore be associated with a dangerously close
passing distance. The bearing will change by more than 5" as the
range closes from 2 miles to 1 mile if the nearest approach is only
0.1 miles or 200 metres. Such a passing distance will bring danger of
collision, especially if the vessels are in an overtaking situation in
relatively shallow water (see pages 94-7).
An appreciable change of bearing at greater ranges does not
necessarily mean that there is no risk of collision. The other vessel
may be making a series of small alterations which have not been
observed. This would apply especially in restricted visibility when
the other vessel is being observed by radar only, but it may also apply

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