Page 53 - Collision Avoidance Rules Guide

vessel. Despite drastic helm and engine action the South African
Pioneer was unable to avoid collision.
Tests carried out by the us Coast Guard have shown that small
icebergs of sufficient size to be dangerous to navigation should
normally be detected at a range of about 4 miles. If the part above
surface is particularly smooth, however, they may remain undetected,
especially when appreciable sea clutter is present. In regions where
small craft and ice are likely to be encountered the speed should be
low enough to enable the vessel to be stopped well within the range
of visibility.

Numbel; location and movement of vessels detected

In determining a safe speed the mariner must take account of the
traffic situation in his vicinity. The greater the number of targets indi-
cated on the radar display the more difficult it may be to determine
risk of collision and to assess the effect of possible manceuvres,
although some radar systems are capable of providing information of
this kind. Vessels detected ahead, or fine on the bow, proceeding in
the opposite direction, will obviously present a greater threat than
vessels observed to be approaching from abaft the beam with a low
closing speed.
Where traffic separation schemes apply a ship using a traffic lane
in restricted visibility may find it dangerous to reduce to a very low
speed when proceeding in the general direction of traffic flow as this
may result in her being frequently overtaken by other ships passing
at close distances. However, a high speed is not necessarily justified
in order to keep pace with other vessels in a traffic lane. The possibil-
ity of encountering crossing vessels and small craft must be taken
into account.

Assessment of visibility
When fog or mist is considered likely to develop the radar should be
in operation. It may be possible to determine the extent of the visi-
bility by observing the radar ranges at which other vessels or navi-
gation marks are first visually sighted, or at which they disappear
from view. At night the probable presence of fog may be indicated by
failure to see the lights of a vessel which gives a strong echo within
the normal visual range.
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