Page 59 - Collision Avoidance Rules Guide

Nevertheless AIS information may be used to assist in collision avoidance
decision-making. When using the AIS in the ship-to-ship mode for anti-
collision purposes, the following cautionary points should be borne in mind
1. AIS is an additional source for navigational information. AIS does not
replace, but supports, navigational systems such as radar target-tracking and
VTS; and
2. the use of AIS does not negate the responsibility of the OOW to
comply, at all times, with the Collision Regulations.

The user should not rely on AIS as the sole information system, making use
of all safety-relevant information available.
The use of AIS on board ship is not intended to have any special impact on
the composition of the navigational watch, which should continue to be
determined in accordance with the STCW Convention.
Once a ship has been detected, AIS can assist in tracking it as a target. By
monitoring the information broadcast by that target, its actions can also be
monitored. Changes in heading and course are, for example, immediately
apparent, and many of the problems common to tracking targets by radar,
namely clutter, target swap as ships pass close by and target loss following
a fast manoeuvre, do not affect AIS. AIS can also assist in the identification
of targets, by name or call sign and by ship type and navigational status.

Appropriate to the prevailing circumstances
The phrase ‘appropriate to the prevailing circumstances and conditions’
indicates that it is not always necessary to use radar to determine
whether risk of collision exists. However, paragraph (a) should not be
interpreted as only requiring radar to be used in restricted visibility.
Visual compass bearings are generally preferable to radar bearings
when vessels are in sight of one another, but the use of radar enables
ranges to be taken. A stand-on vessel can use radar to determine
whether the vessel required to keep out of the way is not taking appro-
priate action or is so close that collision cannot be avoided by the
action of the give-way vessel. A vessel which is obliged to pass close
to another vessel when overtaking can use radar to ensure that there is
a safe passing distance. The effects of interaction and the possibility of
a steering defect should be taken into account.
Vessels in visual sight of one another have even been considered
to be at fault for not using radar to determine whether risk of colli-
sion exists in cases to which the 1960 Rules were applicable. In the
Statue ofliberty-Andulo (1970) the Assessors advised that both the